SOLUTION MANUAL FOR Anatomy & Physiology An Integrative Approach 2nd Edition. Michael McKinley Valer

Anatomy & Physiology An Integrative Approach 2e Michael McKinley Valerie O'Loughlin Theresa Bidle (Solutions Manual (Answer Key) All Chapters, 100% Original Verified, A+ Grade) All Chapters Solutions Manual Supplement files download link at the end of this file.

McKinley/O’Loughlin/Bidle Anatomy and Physiology: An Integrative Approach, 2/e Instructor Answer Key to In-chapter and End-of-chapter Questions Chapter 1 Answers to “What Did You Learn?”

1. Comparative anatomy.

2. Anatomy is the study of structure and form. Physiology is the study of how the structures function.

3. Cardiovascular.

4. Anatomists focus on the form and structure of the small intestine. They examine the cells and tissues that form the small intestine, and describe the layers of the small intestinal wall. Physiologists focus on the function of the small intestine. They examine how the muscle of the smooth intestine propels food through the digestive tract and describe the process by which nutrients are broken down and absorbed. Both anatomists and physiologists know that form and function of the small intestine are interrelated.

5. The ability of organisms to respond to stimuli such as changes in either their external or internal environment provides them with a mechanism for maintaining a constant internal environment, even as the environment around them changes.

6. A higher level of organization does contain all of the levels beneath it. Each level of organization is a function of the arrangement of its subsequent subunits, which are in turn a function of the organization of their subunits.

Therefore, each level organization is dependent on the organization of all of the levels below.

7. The urinary system is responsible for filtering and removing waste products from the blood.

8. A transverse plane, also called a horizontal or cross-sectional plane, would divide the mouth into superior and inferior sections.

9. Proximal.

10. The term antebrachial refers to the forearm, the portion of the upper limb between the elbow and wrist.

11. The lungs are located within the thoracic cavity. The serous membranes surrounding them consist of the parietal pleura lining the inside of the body wall and the visceral pleura lining the individual lungs.

12. Epigastric.

13. A homeostatic system consists of a receptor such as a sensory neuron in the skin or a stretch receptor within a muscle that detects either an internal or external stimulus, a control system that integrates the input from the receptor such as the brain or an endocrine gland, and an effector such as a muscle or a gland that causes changes in response to the stimulus.

14. The body may respond to a drop in temperature by decreasing the diameter of blood vessels carrying blood to the surface of the skin, thereby decreasing the amount of heat lost to external environment. Another response involves stimulation of skeletal muscles, causing “shivering” and thereby generating heat internally.

15. Negative feedback systems involve responses that are in opposition to the stimulus, thereby maintaining the environment near the set point or normal level. Conversely, positive feedback systems entail a series of responses, each increasing in intensity, until a climax event is reached, at which point the system will return to homeostasis.

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16. Diabetes, an inability of the body to maintain blood sugar levels, may result in damage to anatomical structures throughout the body due to high levels of glucose.

Answers to “Do You Know the Basics?”

1. B Feedback: Surface anatomy correlates superficial markings on the surface of the body and skin to deeper anatomical features.

2. C Feedback: Organs are often composed of several tissue types working in concert to perform a common function.

3. A Feedback: An organism’s metabolism is the sum of all of its biochemical reactions.

4. C Feedback: A midsagittal or median plane separates the body into equal right and left halves as compared to simply a sagittal section, which separates the body into unequal right and left portions. There can be numerous sagittal planes but only one possible midsagittal section along the midline of the body.

5. D Feedback: The term proximal is used to describe the position of a structure on an appendage closest to the point of attachment to the trunk. Although in standard anatomical position a structure that is proximal is often also superior, proximal is the correct term for describing the position along an appendage. The term superior may be used to describe positions along the axis of the body, closer to the head.

6. A Feedback: The patellar region is the anterior portion of the knee. The popliteal region is the posterior portion of the knee.

7. A Feedback: The diaphragm comprises the barrier between the superior thoracic cavity and the inferior abdominal cavity. The pelvic cavity is located inferior to the superior edges of the pelvic bones.

8. D Feedback: The pleural cavity surrounding the lungs consists of the parietal pleura lining the internal walls of the thoracic cavity and the visceral pleura lining the surface of the lungs.

9. B Feedback: Homeostasis is an automated process for maintaining a constant internal environment.

10. D Feedback: The effector increasing the stimulus is an example of positive feedback. In a negative feedback system, the response moves the system in opposition to the stimulus, back toward the set point.

11. Anatomy is the study of structure and form, whereas physiology is the study of how the structures function.

It is important to understand the anatomy of a structure in order to understand how it performs its function.

Conversely, understanding the function of an anatomical feature helps to put into perspective the significance of its arrangement.

12. The simplest level of organization within an organism is found at the chemical level and is composed of atoms and molecules. At the cellular level of organization, molecules are organized into cells and subcellular components, forming the basic units of life. Groupings of similar cells performing similar functions are referred to as tissues, and groups of tissues may be found working in concert, forming organs at the organ level of organization. Related groups of organs working together in order to coordinate activities within the organism are called organ systems.

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13. A hierarchical organization, metabolism, growth and development, responsiveness, regulation, and reproduction are characteristics common to all living organisms. All living things are arranged in a hierarchical manner with increasing levels of complexity from molecules to cells. They are capable of metabolism, growth and development, and responsiveness to stimuli. They are also able to regulate their internal environment in order to maintain homeostasis, ultimately surviving long enough to reproduce.

14. The human body consists of eleven organ systems. They are the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, urinary, digestive, and reproductive systems.

15. A body in anatomical position is standing upright with the feet flat on the floor. The upper limbs are at the side of the body with palms facing anteriorly. The head is level and the eyes are looking forward. The anatomic position is the point of common reference used by anatomists and physiologists for accuracy and clarity. It provides an initial point of reference, from which all anatomic parts are described.

16. The forearm is the antebrachial region, the wrist is the carpal region, the chest is the thoracic region, the armpit is the axillary region, the thigh is the femoral region, and the entire foot is the pes.

17. The cranial cavity and vertebral canal are located within the posterior aspect of the body. The cranial cavity houses the brain and the vertebral canal contains the spinal cord.

18. The serous membranes are found lining the compartments of the ventral cavity of the body. They consist of a parietal layer lining the inside of the body wall and a visceral layer covering internal organs. In between the two membranes is a potential space, the serous cavity, which contains serous fluid.

19. A homeostatic system consists of a receptor that detects an internal or external stimulus, a control system that integrates the input from the receptor, and an effector such as a muscle or a gland that causes changes in response to the stimulus.

20. Negative feedback systems involve responses that are in opposition to the stimulus, thereby maintaining the environment near the set point or normal level. Conversely, positive feedback systems entail a series of responses, each increasing in intensity until a climax event is reached, at which point the system will return to homeostasis.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: The pain is coming from a region below the umbilicus, hence it is in the lower portion of the abdomen and it is located on the right side. It is therefore in the right lower quadrant.

2. D Feedback: The right iliac region is located just medial to the pelvic bones.

3. B Feedback: X-rays are not absorbed by soft tissue such as the appendix. They are usually used to visualize dense structures.

4. B Feedback: Sweat glands release sweat at the surface of the skin.

5. B Feedback: Serotonin is a neurotransmitter responsible for regulating both pathways associated with depression in the brain and gastric motility in the stomach. Drugs such as SSRIs are used to treat depression in individuals with low levels of serotonin in the brain by inhibiting its reuptake by neurons. Because the SSRI drugs cannot specifically target the brain, they also have an effect within the digestive system, causing nausea and diarrhea.

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Answers to “Can You Synthesize What You’ve Learned?”

1. Lynn has broken the bones within her forearm, the radius and ulna. She has an abrasion on her chin as well as bruising on her buttocks and thigh.

2. The epinephrine counteracted the effect of the bee sting, acting in opposition to the stimulus; it was therefore an example of negative feedback.

3. X-rays and CT scans are optimal for visualizing dense tissues such as tumors. An MRI or ultrasound would be better suited for examining soft tissues.

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Chapter 2 Answers to “What Did You Learn?”

1.The mass of an atom is determined by the combined number of protons and neutrons within its nucleus. The charge of an atom is determined by the number of positively charged protons and negatively charged electrons.

2.The nucleus of a chlorine atom consists of 17 protons and 18 neutrons. The electrons are arranged into three separate shells; the first shell closest to the nucleus contains two electrons, the second shell contains eight electrons, and the third outer shell contains seven electrons for a total of 17 electrons.

17P 18N

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3. Isotopes are atoms of the same element. They only differ in their number of neutrons, thus they differ in their atomic mass. A radioisotope is unstable because of extra neutrons. Stability can ultimately be reached through the loss of nuclear components in the form of high-energy radiation (e.g., alpha particles, beta particles).

Thus, the radioisotope will decay as radiation is released.

4. The octet rule is the tendency for atoms to lose, gain or share electrons to obtain a complete outer shell and thus become chemically stable.

5. Common cations (positively charged ions) of the human body include: sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), and hydrogen ions (H+). Common anions (negatively charged ions) include: chloride ions (Cl–), bicarbonate ions (HCO3−), and phosphate ions (PO43–).

6. Sodium (atomic number 11), potassium (atomic number 19), calcium (atomic number 20), magnesium (atomic number 12), hydrogen (atomic number 1), and chlorine (atomic number 17) should be highlighted.

7. In order to satisfy the octet rule, atoms may either lose or gain electrons to become chemically stable (have a complete outer shell of electrons). However, a charge is developed because the number of positively charged protons is no longer equal to the number of negatively charged electrons. For example, atoms with only one electron in their outer shell may give up the electron, resulting in a positive cation, now with a full outer shell.

Conversely, atoms with seven electrons in their outer shell may accept an electron from another atom, becoming a negative anion, but now with a full outer shell.

8. Ionic bonds are formed due to an attraction between ions with different charges. Therefore, an ionic bond cannot be formed between two cations; nor can it be formed between two anions.

9. The structural formula exhibits the type and number of atoms in a molecule, and their arrangement within the molecule. In comparison, the molecular formula provides information only for the type and number of atoms in a molecule (but not how the atoms are arranged within the molecule).

10. Isomers are molecules composed of the same type and number of elements, but are arranged differently (i.e., they have the same molecular formula, but a different structural formula).

11. A covalent bond is formed when atoms share electrons in their outer orbitals in order to satisfy the octet rule.

12. Nitrogen is more electronegative that hydrogen, thus it is designated with a partial negative charge, whereas hydrogen is less electronegative than nitrogen and is designated with a partial positive charge.

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13. A covalent bond between atoms of the same element (with both atoms equally electronegative) will result in electrons being shared equally between the two atoms. Thus, the resulting bond is a nonpolar bond. A covalent bond formed between two different atoms (with one atom more electronegative than the other) will result in electrons being shared unequally between the two atoms. Thus, the resulting bond is a polar bond. The more electronegative atom will have a slightly negative charge and the less electronegative atom will have a slightly positive charge.

Note: Because carbon and hydrogen atoms are nearly equal in terms of electronegativity, atoms of these two different elements essentially share electrons equally and form a nonpolar covalent bond between them.

14. Both molecular oxygen (O2) and carbon dioxide (CO2) are nonpolar molecules. (This is significant for understanding how these respiratory gases are transported in the blood, a topic that is covered in chapter 23.)

15. A hydrogen bond is a weak attraction between a partially positive hydrogen atom within a polar molecule and a partially negative atom within a polar molecule (usually oxygen, but sometimes nitrogen).

16. Hydrogen bonds are the intermolecular bonds that are significant in determining the properties of water.

17. Surfactant is required to decrease surface tension (the cohesive attraction between water molecules) in the alveoli of the lungs. Body temperature is regulated through sweating because of water’s high heat of vaporization.

Sweating is less effective on a humid day because of the increased water in the environment that impedes additional water evaporating from the skin.

18. Nonelectrolyte molecules such as glucose dissolve but do not dissociate in water. Electrolytes such as sodium chloride (NaCl) both dissolve and disassociate into constituent ions in water, forming a solution capable of conducting electricity.

19. In an aqueous environment, amphipathic molecules such as phospholipids will orient themselves so that their hydrophobic domains face each other while the hydrophilic portions are exposed to water. This is the basis for the arrangement of phospholipids within a bilayer and a micelle.

20. Each water molecule can disassociate into one positively charged hydrogen ion and one negatively charged hydroxyl ion. It is considered neutral since it has an equal distribution of positive and negative charges.

21. An acid dissociates in water and releases hydrogen ions.

22. pH is a measure of the relative amounts of H+ in a solution. The relationship between [H+] and pH is inverse. As [H+] increases, pH decreases, whereas as [H+] decreases, pH increases.

23. A buffer helps prevent pH changes if either excess acid or base is added. It acts either to accept H+ from excess acid or donate H+ to neutralize excess base. (Buffers act as H+ sponges, absorbing H+ if acid is added and releasing H+ if base is added.)

24. Blood would be characterized as a suspension because blood cells settle to the bottom of a tube when left standing.

25. Blood is also considered a colloid because it contains a mixture of proteins within the liquid portion of the blood, and it is a solution because it contains salts, glucose and other dissolved nonprotein substances in the plasma.

26. The concentration of a solution may be expressed as (1) mass of solute per volume of solution [mass/volume], (2) grams of solute per 100 milliliters (mL) of solution [mass/volume percent], (3) moles of solute per liter of solution [molarity], and (4) moles of solute per kilogram of solvent [molality].

27. Biological molecules typically contain carbon (C), hydrogen (H), and oxygen (O) and in some cases may also contain nitrogen (N), phosphorus (P), and sulfur (S). Hydrogen is the element that both (a) forms a common ion and (b) is a common element in biomolecules.

28. Carboxylic acids and phosphates are capable of acting as acids.

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29. A polymer is composed of repeating monomer subunits. Proteins are composed of amino acid monomers, carbohydrates contain sugar monomers, and nucleic acids have nucleotide monomers.

30. Lipids are fatty, water-insoluble, hydrophobic molecules and do not typically dissolve in water.

31. Phospholipids are amphipathic molecules that form chemical barriers of cell membranes. They contain both a hydrophilic head group (that dissolves in water) and a pair of hydrophobic fatty acid tails (that do not dissolve in water), making them ideally suited for forming cellular membranes.

32. Glycogen is composed of repeating glucose monomers or subunits and is stored by animals within the liver and skeletal muscle cells.

33. Fructose, galactose, and glucose are monosaccharides. Sucrose, maltose, and lactose are disaccharides. Glycogen and starch are polysaccharides.

34. Nucleic acids store and transfer genetic information within cells. They ultimately determine the types of proteins synthesized within cells.

35. RNA molecules contain a ribose sugar in their nucleotides rather than the deoxyribose sugar that is within the nucleotides of DNA. The nucleotides of both RNA and DNA may contain the nitrogenous bases of adenine, guanine, and cytosine. The base uracil is present within nucleotides of RNA. In comparison, the base thymine is present in the nucleotides composing DNA. RNA is a single strand, whereas DNA is a double strand (double helix).

36. Amino acids are the monomers of a protein and they are covalently linked by peptide bonds.

37. A dipeptide consists of 2 amino acids, an oligopeptide contains 3 to 20 amino acids, a polypeptide contains 21 to 199 amino acids, and a protein consists of 200 or more amino acids. The term protein is generally used to refer to oligopeptide, polypeptide and protein.

38. The R group of leucine is a nonpolar hydrocarbon, making it a nonpolar amino acid.

39. The tertiary structure refers to the three-dimensional shape exhibited by one completed polypeptide chain. The quaternary structure refers to the three-dimensional shape of two or more polypeptide chains that form the functional protein.

40. Denaturing a protein changes its conformation and affects its activity. Exposure of a protein to higher than normal concentration of hydrogen ions (a decrease in pH) results in the positively charged H+ binding with negatively charged structures that were participating in electrostatic interactions that were holding the protein in its final shape. The loss of these electrostatic interactions between the amino acids that compose the protein results in its unfolding (or denaturation).

Answers to “Do You Know the Basics?”

1. C Feedback: Isotopes are atoms of the same element that have the same number of protons and electrons, but differ in the number of neutrons.

2. A Feedback: Lipids are hydrophobic molecules and are not soluble (do not dissolve) in water.

3. C Feedback: Water has a high specific heat, allowing it to absorb and release energy without changing temperature. In addition, the high heat of vaporization for water allows it to dissipate a large amount of energy during evaporative cooling of the skin.

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4. D Feedback: A pH less than 7.0 is acidic and a pH greater than 7.0 is basic.

5. D Feedback: The formed elements of blood act as a suspension. Dissolved proteins in the plasma act as a colloid. The numerous dissolved solutes also make blood a solution.

6. A Feedback: Triglycerides are not considered polymers because they are not composed of repeating monomer subunits.

7. C Feedback: Glucose is stored in animal tissues as glycogen.

8. B Feedback: Although phosphates which contain phosphorus are common ions in the body, phosphorus itself is not a common ion.

9. B Feedback: A hydrogen bond is an intermolecular attraction between a slightly positive hydrogen atom within a polar molecule and a slightly negative atom (e.g., oxygen, nitrogen) in a polar molecule.

10. B Feedback: Denaturing a protein changes its conformation. Excessive denaturation can permanently affect protein structure and possibly its function as well.

11. Common cations of the human body include sodium ions (Na+), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), and hydrogen ions (H+). Common anions include chloride ions (Cl-), bicarbonate ions (HCO3-), and phosphate ions (PO43-).

12. Polar bonds have varying degrees of unequal electron sharing between two different atoms, except for C-H, an oxygen atom bonded to a hydrogen atom. Oxygen, the more electronegative of the atoms, will have a stronger pull on the electrons and will thus have a slightly more negative charge around it, while the hydrogen atom will be relatively more positive (or less negative). A polar molecule is a molecule that contains a prevalence of polar bonds between the atoms that compose it. For example, water is a polar molecule composed of two polar covalent bonds between the oxygen atom and each hydrogen atom.

13.

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14. Polar molecules (e.g., glucose) will dissolve in water because hydrogen bonds are formed between the water and the polar molecules. The polar molecule does not dissociate, remaining intact as in this example of a glucose molecule. In comparison, ionic compounds both dissolve and dissociate. Ionic compounds such as sodium chloride (NaCl) will disassociate in water because the polar water molecules will disrupt the electrostatic interactions between sodium and chloride ions, thereby separating them.

15. An acid contributes hydrogen ions to a solution, making it more acidic (having a lower pH). A base binds hydrogen ions from a solution, making it more basic (having a higher pH). pH is the measure of hydrogen ions in a solution. A buffer is capable of either absorbing or releasing hydrogen ions, thereby helping to prevent pH changes when acids or bases are added.

16. The concentration of a solution may be expressed as either the ratio of the mass of solute compared to the volume of the solution (mass/volume), as the percent of mass of solute in 100 milliliters of solution (mass/volume %), as the number of moles of solute per liter of solution (molarity), or the number of moles of solute per kilogram of solvent (molality).

17. Proteins are composed of amino acids (repeating units); carbohydrates are composed of simple sugars (repeating units); nucleic acids are composed of nucleotides (repeating units); but lipids are not composed of repeating units.

There are four primary types of lipids: triglycerides (composed of glycerol and fatty acids); phospholipids (composed of glycerol, two fatty acids, a phosphate, and various organic groups); steroids (cholesterol, steroid hormones, and bile salts—composed predominantly of hydrocarbons that differ in the side chains extending from the rings); and eicosanoids (prostaglandins, thromboxanes, and leukotrienes—composed of modified 20-carbon fatty acids synthesized from arachidonic acid).

18. Nucleotides (composed of a sugar, phosphate, and a nitrogenous) that compose DNA and RNA contain nitrogen that forms a nitrogenous waste called uric acid. Amino acids contain an amine functional group, —NH2, that is converted to a nitrogenous waste called urea. Both uric acid and urea must be effectively eliminated by the kidney for an individual to remain healthy.

19. In an aqueous environment, amphipathic molecules such as phospholipids will orient themselves so that their hydrophobic domains face each other while the hydrophilic domains are exposed to water. This is the basis behind the arrangement of phospholipids within a phospholipid bilayer of the plasma membrane of a cell.

20. A protein’s function is dependent upon the retention of its normal 3-dimensional shape. Denaturation is a change in the conformation of a protein that changes/affects its activity. Exposure of a protein to either an increase in temperature or a pH outside of its normal environment can denature the protein by disrupting electrostatic interactions such as ionic bonds within the molecule.

An increase in temperature can weaken the intramolecular attractions between the amino acids in the primary structure of the protein strand, causing the protein to unfold or denature such that it can no longer function normally.

Changes in H+ concentration that are associated with changes in pH interfere with the electrostatic interactions within the protein that hold it in its 3-dimensional shape. Exposure of a protein to higher than normal concentration of hydrogen ions (a decrease in pH) results in the positively charged H+ binding with negatively charged structures that were participating in electrostatic interactions that were holding the protein in its final shape. Exposure of a protein to lower than normal concentration of hydrogen ions (an increase in pH) results in the positively charged H+ that were participating in electrostatic interactions and holding the protein in its final shape being removed. The loss of these electrostatic interactions between the amino acids that compose the protein results in its unfolding (or denaturation).

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: Surface tension is high within the air sacs in the lungs of premature infants that are not producing sufficient surfactant. Surfactant is a detergent-like substance that prevents hydrostatic interactions between water molecules, thereby preventing the lungs from collapsing and the alveolar walls from sticking together. Premature babies often lack the ability to produce surfactant and are at risk for respiratory problems.

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2. B Feedback: Electrolytes such as sodium ions, potassium ions, and chloride ions are capable of conducting electricity.

Nonelectrolytic molecules such as glucose are not able to conduct electricity.

3. B Feedback: Isotopes are atoms of the same element that differ in their number of neutrons. In a radioisotope the extra neutrons will decay and be released as radiation, which may be measured or visualized during a diagnostic test.

4. D Feedback: Calcium (Ca2+) ions are an important structural component of bone tissue.

5. C Feedback: Proteins consist of covalently bonded amino acids held together by peptide bonds. If insulin is administered orally, the peptide bonds are broken by enzymes of the digestive system (to form individual amino acids).

Answers to “Can You Synthesize What You’ve Learned?”

1. High-energy radiation can cause mutations within DNA. 2. The number of hydrogen ions in the blood increases, resulting in a lower pH (a condition called acidosis). The increasing number of hydrogen ions may interfere with the hydrostatic interactions holding proteins together, thus denaturing the proteins.

3. The drug would regulate the levels of the monosaccharide glucose within the blood.

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Chapter 3 Answers to “What Did You Learn?”

1. Kinetic energy is the energy of motion. Movement of sodium ions along a concentration gradient or the movement of electrons from a higher to lower energy state are both examples of kinetic energy.

2. The movement of muscle is an example of mechanical energy, a form of kinetic energy that involves the movement of an object due to an applied force.

3. Even though energy can neither be created nor destroyed, it can be transformed or converted from one form to another. Such transformations are not completely efficient, always resulting in the release of some of the energy as heat, which is not available to do work.

4. Reactants are the substrates or substances that are present prior to a chemical reaction. The reactants are converted to products during the reaction.

5. Formation of a complex molecule from simpler chemical structures would be classified as: (a) a synthesis reaction, (b) an endergonic reaction, and (c) a form of anabolism.

6. ATP is the molecule that produced by exergonic reactions and used to couple exergonic reactions to endergonic reactions (chemical reactions that require an input of energy) and other energy-requiring processes within the cell.

7. When equilibrium is disturbed in a reversible reaction, the system will adjust and the reaction is driven toward either the reactants or the products until equilibrium is reestablished. For example, an increase in substrates drives the chemical reaction to the right (making more product) until a new equilibrium is reached.

8. Initially, the effect of a fever (elevation in temperature) increases the kinetic energy of the molecules, providing enough energy to break chemical bonds. The consequence of high fever may result in the denaturing of proteins and potentially cause the death of the cell (and possibly the death of the individual).

9. Enzymes are catalysts that decrease the energy of activation required for a chemical reaction to proceed.

10. The active site is a region in the enzyme that is the temporary binding site for the substrate to the enzyme.

11. Enzymes are proteins that catalyze metabolic reaction by lowering the activation energy necessary for the reaction. The structure of the protein directly affects its affinity for its specific substrate. (1) Substrate enters the enzyme’s active site and temporarily binds to it, forming an enzyme-substrate complex. (2) Binding of substrate into the active site induces conformational changes in the enzyme; this response is referred to as the induced-fit model of enzyme function. (3) Chemical bonds in the substrate are stressed by changes in the enzyme shape. This lowers the Ea, (activation energy) so that bonds in the substrate(s) are more easily broken and new chemical bonds may be formed. (4) A new molecule (called [a] product[s]) is released from the enzyme. Inorganic cofactors are attached to enzymes and may be required for the normal function of some enzymes.

12. The name of an enzyme is usually based upon the name of the substrate or the product involved in the chemical reaction, or sometimes the name of the enzyme subclass. The suffix -ase is added to the final word of the name.

13. The rate of an enzyme-catalyzed reaction may be increased as the concentration of substrate is increased, until all of the enzyme molecules are saturated. Enzymes function most efficiently at their optimal temperature. Decreasing temperature from an enzyme’s optimum range will decrease its activity. Increasing temperature increases the rate of the reaction until enzymes denature. Changing pH in either direction (increase or decrease) from its optimal pH will readily denature the protein as the change in hydrogen ion concentration interferes with electrostatic interactions within the enzyme, denaturing it.

14. Inhibitors prevent an enzyme from converting substrate to product. Competitive inhibitors affect enzyme activity by competing with substrates at the active site of the enzyme. Noncompetitive inhibitors do not resemble the

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substrate, but they inhibit an enzyme by binding to a site on the enzyme other than the active site (a site called the allosteric site). This modulates the shape of the enzyme altering the shape of its active site.

15. A metabolic pathway is formed by numerous enzymes. Each enzyme catalyzes one progressive change to its specific substrate molecule and then releases the product. Thus, the product of one enzyme becomes the substrate of the next enzyme. Negative feedback is a means to regulate the activity of metabolic pathways. The product from a metabolic pathway acts as an allosteric inhibitor to turn off an enzyme early in the pathway and regulate enzyme activity.

16. Phosphorylation (the adding of a phosphate group) and dephosphorylation (the removal of a phosphate group) are processes that regulate enzymes by turning on some enzymes and turning off other enzymes.

17. The overall chemical reaction for cellular respiration of glucose is: C6H12O2 + 6 O2 → 6 CO2 + 6 H2O. The oxidation of glucose, an exergonic reaction, results in a step-by-step enzymatic breakdown of glucose with the accompanying release of energy to synthesize ATP. If oxygen is available, glucose is completely broken down and carbon dioxide and water are formed.

18. The four stages of cellular respiration are (1) glycolysis within the cytosol of the cell, and three other stages which are (2) the intermediate stage, (3) the citric acid cycle (or Krebs cycle), and (4) the electron transport system, all of which occur within the mitochondria.

19. Glycolysis is a process that occurs within the cytosol and does not require oxygen. The net reaction entails the breakdown of glucose (a 6-carbon molecule) into two pyruvate molecules (each a 3-carbon molecule). The reaction involves the initial input of two molecules of ATP and yields four molecules of ATP, for a net yield of two molecules of ATP. Two molecules of NAD+ are also reduced to form NADH (and H+) from energy released during the oxidation of glucose.

20. Pyruvate may either enter a mitochondrion (if sufficient oxygen is available) to be completely oxidized to carbon dioxide [with the energy released in its chemical bonds] or (if oxygen is lacking) be converted to lactate (a process described in later section in detail).

21. The intermediate stage of cellular respiration is an aerobic process (requires oxygen) that occurs within mitochondria, which “links” the metabolic pathway of glycolysis (that occurs in the cytosol) with the metabolic pathway of the citric acid cycle. During this process CO2 is released from pyruvate (through decarboxylation) and two electrons and a hydrogen ion are transferred to NAD+ to form. (NOTE: this process would occur twice for each glucose molecule).

22. The citric acid cycle is an aerobic process that occurs within the matrix of mitochondria. It uses acetyl CoA as the initial substrate and forms two CO2 molecules and one CoA molecule as the products. The oxidation of acetyl CoA yields: one molecule of ATP, three molecules of NADH, one molecule of FADH2. (NOTE: this process would occur twice for each glucose molecule).

23. Cellular respiration of one molecule of glucose yields: two molecules of ATP and two molecules of NADH during glycolysis, two molecules of NADH during the intermediate stage (per original glucose molecule), two molecules of ATP, six molecules of NADH, two molecules of FADH2 during the citric acid cycle (per original glucose molecule).

24. NADH and FADH2 serve as coenzymes to temporarily hold energy by binding electrons and hydrogen released during the breakdown of glucose during glycolysis, the intermediate stage, and the citric acid cycle. These coenzymes hold the electrons until the electrons are transferred to the electron transport chain, which allows the formation of ATP through oxidative phosphorylation.

25. The three primary steps of the electron transport system are the following: (1) Electrons are transferred from coenzymes to O2, (2) Proton gradient is established, and (3) Proton gradient is harnessed to form ATP.

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26. Glycolysis yields a net of two molecules of ATP for every molecule of glucose. Under aerobic conditions the complete oxidation of one molecule of glucose yields a net of 30 molecules of ATP. 27. In conditions of insufficient oxygen, pyruvate is converted to lactate in the cytosol. This facilitates the regeneration of two molecules of NAD+, which can then be utilized to continue with the glycolysis of more glucose, yielding limited amounts of ATP (2 ATP per glucose).

28. Fatty acids are enzymatically changed two carbon units at a time to form acetyl CoA. This is called betaoxidation of fatty acids. Acetyl CoA is oxidized within mitochondria (through the intermediate stage and the citric acid cycle). Thus, because processes that occur within mitochondria require oxygen, fatty acids can only be oxidized is sufficient oxygen is available.

Answers to “Do You Know the Basics?”

1. A Feedback: Chemical energy is converted to mechanical energy. Energy from the hydrolysis of ATP (which releases chemical energy from the high energy bond between the second and third phosphate) is used to move a body part in response to an applied force exerted by the muscle contraction.

2. A Feedback: Oxidation-reduction reactions involve the exchange of electrons between the oxidizing and the reducing agent.

3. B Feedback: Increasing (or decreasing) pH interferes with electrostatic interactions within the enzyme, causing denaturation of the enzyme (and a subsequent decrease in enzyme activity).

4. C Feedback: Since ATP does not bind to the active site of phosphofructokinase, it is not a competitive inhibitor. It is an example of an allosteric/noncompetitive inhibitor.

5. D Feedback: Enzymes are very specific for their substrate and are therefore each enzyme is capable of catalyzing only one specific reaction.

6. A Feedback: Glycolysis yields two molecules of pyruvate from one molecule of glucose.

7. D Feedback: NAD+ and FAD are coenzymes involved in oxidation-reduction reactions where they bind electrons and hydrogen that are released from both glucose and its (glucose's) breakdown products.

8. A Feedback: Glycolysis is able to continue when there is insufficient oxygen available because oxygen is not required (i.e., glycolysis is not aerobic).

9. C Feedback: One molecule of glucose may yield a net of 2 molecules of ATP if insufficient oxygen is available and a net of 30 molecules of ATP if sufficient oxygen is present.

10. D Feedback: Oxidative phosphorylation involves the transfer of electrons from NADH and FADH2 to oxygen in the electron transport chain, the establishment of a proton gradient through the use of energy from electrons passed along the electron transport chain, and finally using the proton gradient to form ATP as H+ moves down its

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concentration gradient and is transported across the inner mitochondrial membrane by ATP synthetase to form bonds between ADP and Pi. 11. Chemical energy is energy stored in chemical bonds; it is a form of potential energy. Energy stored in glycogen or triglycerides represents chemical energy. The remaining forms of energy are classified as forms of kinetic energy.

Electrical energy is the movement of charged particles such as electrons along a wire or the propagation of an impulse in a neuron (nerve cell). Mechanical energy involves the movement of an object due to an applied force; muscle contraction is an example of mechanical energy. Sound energy is movement of compressed molecules through a medium (e.g., air) that is initiated by a vibrating object; vibration of the vocal cords of the larynx is an example. Radiant energy is the movement of electromagnetic waves that travel in the universe and vary in wavelength and frequency; visible light that is perceived by the eye is an example of radiant energy.

12. Chemical reactions are classified as reactions that cause (1) changes in chemical structure, (2) changes in chemical energy, and (3) whether the reaction is irreversible or reversible. Oxidation-reduction reactions are exchange reactions during which electrons are transferred from one substance to another.

13. ATP cycling is the continuous formation of ATP (from ADP and Pi) during cellular respiration and then the splitting of ATP back into ADP and Pi for the energy-requiring cellular processes.

14. Enzymes are globular proteins that catalyze metabolic reactions (both decomposition and synthesis reactions) by lowering the activation energy necessary for the reaction. The substrate enters the active site of the enzyme, and the enzyme temporarily binds with the substrate to form an enzyme-substrate complex. Entry of the substrate into the active site induces the conformation (structure) of the enzyme to change slightly, resulting in an even closer fit between substrate and enzyme. This response is referred to as the induced-fit model of enzyme function. Stress on chemical bonds in the substrate molecule is caused by the change in enzyme shape. Consequently, this stress lowers Ea, and the bonds in the substrates are more easily broken, permitting new chemical bonds to be formed. The newly formed molecule, now called the product, is released from the enzyme. The enzyme is then free to repeat the process again and again with other substrates.

15. A metabolic pathway consists of a series of enzyme-catalyzed reactions. The product of one enzyme becomes the substrate of the next enzyme in the metabolic pathway. Often the final product of the pathway serves as an allosteric inhibitor of enzymes within the pathway, causing a conformation change in the protein. This rearrangement may affect the affinity for the substrate at the enzymes’ active sites, thereby providing for negative feedback within the pathway.

16. Glycolysis is a process that occurs within the cytosol of a cell and does not require oxygen. The net reaction entails the breakdown of glucose (a 6-carbon molecule) into two pyruvate molecules (each a 3-carbon molecule).

The reaction involves the initial input of two molecules of ATP and yields four molecules of ATP, for a net yield of two molecules of ATP. Two molecules of NAD+ are also reduced to form NADH and H+ from electrons and protons released during the oxidation of glucose.

17. If sufficient oxygen is available, pyruvate enters a mitochondrion to complete its aerobic breakdown yielding carbon dioxide and water. It insufficient oxygen is present, pyruvate is converted to lactate in the cytosol. This facilitates the regeneration of two molecules of NAD+, which can then be utilized for continuing the steps of glycolysis to yield two molecules of ATP per glucose molecule.

18. Oxygen serves as the final electron acceptor of the electron transport chain during oxidative phosphorylation.

Molecular oxygen (O2) in the mitochondrial matrix is split and each oxygen atom along with electrons from the electron transport chain combine with two hydrogen ions, yielding a molecule of water.

19. The carbon in carbon dioxide is liberated from glucose (or other fuel molecules such as fatty acids) during cellular respiration.

20. Healthy respiratory and cardiovascular systems provide metabolically active tissues with adequate oxygen to drive efficient aerobic respiration (which yields greater amounts of ATP than if there is insufficient oxygen). Tissues deprived of oxygen will not be able to burn fuels efficiently nor produce adequate amounts of ATP.

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Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: The enzyme tyrosinase is required to convert tyrosine to melanin.

2. D Feedback: Decreased respiratory function will lead to a deficiency in oxygen and thus both an increase in glycolysis and a decrease in aerobic cellular respiration. This results in an accompanying decrease in ATP production.

3. B Feedback: The increase in substrate (CO2) will drive the reversible reaction to the right with an increase in the synthesis of carbonic acid (H2CO3), which will spontaneously decompose to hydrogen (H+) and bicarbonate ions (HCO3−). The may result in a decrease in the pH of the blood, a condition known as respiratory acidosis.

4. D Feedback: Individuals with anemia, asthma, or heart failure would have a diminished capacity for delivering oxygen to tissues. An athlete would have optimized capacity for oxygen transport and therefore normal ATP production that occurs through aerobic cellular respiration.

5. C Feedback: We could eat more and not gain weight because the energy that is released from glucose and other fuel molecules (e.g., fatty acids) that are metabolized within brown fat would generate heat during the electron transport chain instead of ATP. The consequence would be a warmer body.

Answers to “Can You Synthesize What You’ve Learned?”

1. An asthma attack would decrease Tiffany’s ability to ventilate her lungs with air. The result would be a decrease in the amount of oxygen reaching her tissues and less energy production because of a decrease in aerobic cellular respiration.

2. A patient’s aerobic fitness corresponds directly to the patient's ability for ATP production. Increased fitness provides for more efficient delivery of oxygen to tissues, allowing for effective aerobic cellular respiration of fuels.

3. If inhibition of a metabolic pathway does not occur, the product will accumulate.

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Chapter 4 Answers to “What Did You Learn?”

1. Electron microscopy utilizes electrons rather than photons of light to ‘illuminate’ the specimen. This provides greater magnification and improves resolution (the ability to see detail).

2. A human oocyte (which is about 120 micrometers in diameter) is larger than an erythrocyte (which is about 7 to 8 micrometers in diameter).

3. The three main structural features of a cell include the plasma membrane, nucleus, and cytoplasm. The plasma membrane forms the outer, limiting barrier of a cell; the nucleus is the largest structure within a cell, it is enclosed by a nuclear envelope, and it houses both the genetic material (DNA) and a nucleolus; and the cytoplasm that includes the cytosol, organelles, and inclusions.

4. The plasma membrane forms the outer, limiting barrier of the cell and maintains its integrity.

5. Most of the plasma membrane lipids are phospholipid molecules organized into a bilayer. The hydrophobic (“water fearing”) tails of each layer are oriented toward each other, whereas the hydrophilic (“water loving”) heads are exposed to aqueous environments. Therefore, the lipid portion of the plasma membrane is insoluble in water, which ensures that it will not dissolve when it comes into contact with water.

6. Integral membrane proteins are embedded within and extend across the phospholipid bilayer. Transport proteins provide the means for moving materials across the plasma membrane. Transport proteins include channels, carriers, pumps, symporters, and antiporters.

7. O2 and CO2 do not require transporters because they are both small and nonpolar molecules. They can pass through the plasma membrane phospholipid bilayer by simple diffusion.

8. Ions and small polar molecules may be transported across the plasma membrane by facilitated diffusion. Ions diffuse through water-filled protein channels, each of which is specific for one type of ion by a process called channel-mediated facilitated diffusion. Small polar molecules require carrier proteins, which change shape when they bind to the small polar molecules thus permitting transport of the molecule across the membrane by the process called carrier-mediated facilitated diffusion.

9. Osmosis is the passive movement of water through a selectively permeable (semipermeable) membrane.

10. The tonicity of a cell placed into an isotonic solution will not change because both the solution and the cytosol have the same relative concentration of solutes. A cell placed into a hypotonic solution will experience an increase in tonicity because of a net movement of water into the cell. Conversely, a cell placed into a hypertonic solution will lose tonicity because of a net movement of water out of the cell.

11. There is always a net movement of water toward (c) a hypertonic solution.

12. Secondary active transport couples the kinetic energy from the movement of one type of substance (e.g., Na+) down its concentration gradient to move another type of substance against its gradient. Note that these two types of molecules can be moved in the same direction (symport secondary active transport) or in the opposite direction (antiport secondary active transport).

13. A white blood cell engulfing a microbe is an example of phagocytosis.

14. The resting membrane potential (RMP) is the electrical charge difference at the plasma membrane when a cell is at rest. The RMP ranges in value from –50 mV to –100 mV. 15. The resting membrane potential is established by specific types of ions diffusing across the plasma membrane through leak channels: K+ leaks out of a cell and Na+ leaks into a cell. The amount of each ion that diffuses is

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dependent upon both the electrochemical gradient and the number of leak channels present within the plasma membrane. The Na+/K+ pumps maintain the concentration gradients for both Na+ and K+.

16. Cells communicate by direct contact through the interaction of the glycocalyxes of two cells. Examples include: the recognition of cells by the immune system, the interaction of sperm with an oocyte at the onset of fertilization, and the contact inhibition to prevent overgrowth of skin tissue at the site of injury.

17. Enzyme receptors function as protein kinase enzymes and are activated to directly phosphorylate other enzymes (which may either turn the enzyme on or off) in response to the binding of a ligand; G protein-coupled receptors also involve protein kinase activation: however, these enzymes are activated indirectly through the G protein that serves as an intermediate molecule.

18. The endoplasmic reticulum is an extensive interconnected membrane network that varies in shape (e.g. tubules, sacs), but has one continuous lumen. It extends from the nuclear envelope to the plasma membrane. Its membrane surface is a point of attachment for ribosomes and enzymes. Rough endoplasmic reticulum (RER) forms proteins and glycoproteins and the smooth endoplasmic reticulum (SER) synthesizes lipids. Transport vesicles containing these molecules are formed by the pinching off of sections of the ER. The vesicles fuse with the Golgi apparatus.

The Golgi apparatus has several elongated, flattened saclike membranous structures called cisternae, which exhibit a distinct polarity: a cis-face that is closer to the ER and a trans-face with larger flattened sacs. The Golgi modifies, packages, and sorts proteins before they are shipped out for different fates.

19. Lysosomes digest unwanted organelles (and also contents of endocytosed vesicles, and the cellular contents following death of the cell). Peroxisomes function in both digestion of molecules (e.g., fatty acids, amino acids) and producing hydrogen peroxide in the process, and the synthesis of specialized lipids (e.g., bile salts).

20. These non-membrane bound organelles have the following functions: (a) proteasomes function in digesting unwanted proteins; (b) the cytoskeleton forms the structural support of a cell; (c) ribosomes synthesize proteins, and (d) centrioles function in cell division.

21. Both microvilli and cilia are cell surface extensions of the plasma membrane supported by protein. (a) Microvilli are thin, microscopic membrane extensions from the surface of the plasma membrane that serve to increase the surface area of a cell for more efficient membrane transport. Microvilli are shorter, wider, and more densely packed than cilia and are supported by microfilament protein. (b) Cilia are small hair-like projections supported by microtubules that function in moving material along the cell surface. They contain both cytoplasm and supportive microtubule proteins, and are enclosed by the plasma membrane.

22. Cellular junctions connect and support cells. (a) Desmosomes provide resistance to mechanical stress at a single point; (b) Gap junctions allow passage of ions between cells, and (c) Tight junctions prevent leakage between cells.

23. Nuclear pores are open passageways formed by proteins that extend through fused regions of the nuclear envelope. They permit the movement of large molecules into or out of the nucleus including protein molecules into the nucleus and RNA molecules out of the nucleus.

24. The nucleolus is a dark-staining, usually spherical body located within the nucleus. It functions in the formation of the large and small ribosomal subunits.

25. DNA in the nucleus forms enormous macromolecules that house most of the genetic material of the cell. DNA is associated with nuclear proteins called histones to form nucleosomes, which are arranged in a loosely coiled structural arrangement called chromatin. (The chromatin strands condense into chromosomes in preparation for cell division.) A gene is a specific, discrete functional unit of DNA, which is responsible for the production of a specific protein.

26. Three major structures are required for transcription: DNA, ribonucleotides, and the enzyme RNA polymerase.

Transcription involves the arrangement of ribonucleotides along a functional segment of the DNA template (a gene) to form a new RNA molecule. Within the nucleus, a segment of the DNA unwinds at the gene with the breaking of

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hydrogen bonds in between the two complementary DNA strands. Bases of ribonucleotides are complementary base-paired with bases of the DNA, a process assisted by the enzyme RNA polymerase.

27. A codon is a three nucleotide base unit sequence of mRNA. The anticodon is a three nucleotide base unit sequence of tRNA. The anticodon serves two functions. (1) Its sequence (e.g., UAC) determines the specific amino acid (e.g., methionine) to which a given tRNA attaches, a process facilitated by aminoacyl-tRNA synthetase prior to translation (synthesis) of the protein. (2) The anticodon of each tRNA is to serve as the “adapter site” for binding a tRNA to its complementary codon of an mRNA during translation.

28. Translation (or synthesis of a protein) involves three processes: initiation, elongation, and termination. During initiation, the small subunit, large subunit, mRNA, and the first charged tRNA (tRNA with anticodon UAC and holding methionine amino acid) form a complex. This tRNA is in the P site of the ribosome. During elongation the following steps occur repeatedly: (a) a charged tRNA with its amino acid attached is positioned in the A site of the ribosome. The specific tRNA is based on complementary base pairing of the codon of the mRNA and the anticodon of that charged tRNA. (b) A peptide bond forms between the two amino acids (one in the P site and the other in the A site). (c) At this point the first tRNA is released and the ribosome shifts down one codon on the mRNA. The process continues until a stop codon enters the A site signaling the termination of translation. Termination occurs when a stop codon (UAA, UAG, or UGA) enters the A site to end translation. A release factor enters the A site at this point instead of a charged tRNA. When the ribosome hits the factor bound to the mRNA stop codon, the two subunits of the ribosome are separated from the mRNA and the newly synthesized protein is released.

29. The genetic code of DNA is responsible for directing the synthesis of proteins.

30. Chromatin is an uncoiled arrangement of DNA in the nucleus. It is well suited to facilitate transcription and DNA replication. Chromosomes are highly organized, tightly coiled masses that are a condensed form of DNA, which is better suited for the process of cell division.

31. During the S phase of interphase, double helix strands of each of the 46 chromosomes are replicated. DNA replication entails (1) the unwinding of the DNA double helix, (2) the separation of parent strands by breaking hydrogen bonds between the complementary bases, (3) the assembly of new identical DNA strands by DNA polymerase, which complementarily base-pairs free deoxyribonucleotides using both parent strands as templates, and (4) the restoration of DNA double helix as the DNA double strands form their coiled, helix structure.

32. Two distinct events occur during Mitotic Phase (mitosis, which is the division of the DNA within the nucleus for form two nuclei, and cytokinesis, which is the division of the cytoplasm to form two cells with each having one of the nuclei).

MITOSIS: There are four stages in mitosis: [1] Prophase: chromatin supercoils into chromosomes, the nucleolus breaks down and disappears, spindle fibers begin to grow from centrioles, centriole pairs move to opposite poles of the cell, and the nuclear envelope disassembles; [2] Metaphase: chromosomes are aligned in the equatorial plate as spindle fibers attach to the centromere of each chromosome and move them into the center of the cell; [3] Anaphase: spindle fibers move sister chromatids apart toward the cell’s poles (and each sister chromatid, with its own centromere, is now considered a chromosome); and [4] Telophase: chromosomes arrive at each cell pole, chromosomes uncoil, each new nucleus forms a nucleolus, the mitotic spindle breaks up and disappears, and a new nuclear envelope forms around each of the two sets of chromatin.

CYTOKINESIS: Division of the cytoplasm between the two newly forming cells – each with their own nucleus.

33. Apoptosis is a process of programmed cell death. DNA is digested into small fragments.

Answers to “Do You Know the Basics?”

1. C Feedback: Not all cells are capable of cell division. All cells are capable of acquiring nutrients, maintaining a plasma membrane, and removing waste.

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2. D Feedback: The plasma membrane is an equal mixture (by weight) of proteins and lipids. Most of its functions are determined by proteins. These include: transport of substances, cell surface receptors, identity markers, enzymes that catalyze chemical reactions, anchoring sites for the cytoskeleton, and cell-adhesion proteins for cell-to-cell attachments.

3. B Feedback: Facilitated diffusion through either a channel or a carrier protein requires a concentration gradient but does not require energy from ATP. The random movement of molecules and ions allows substances to diffuse from where the substance is more concentrated to where it is less concentrated.

4. C Feedback: Since the movement of one substance down its concentration gradient is coupled to the movement of another molecule against its particular gradient, this is an example of secondary active transport. Because both molecules are moving in the same direction, the transport molecule would be a symporter. Thus the process is symport secondary active transport.

5. A Feedback: Lysosomes, the Golgi apparatus, and the endoplasmic reticulum are all composed of phospholipid membranes. Ribosomes are non-membrane bound organelles (composed of protein the rRNA).

6. A Feedback: The smooth endoplasmic reticulum is responsible for lipid synthesis and the detoxification of lipidsoluble molecules such as alcohol.

7. C Feedback: Proteasomes are responsible for degrading malformed, damaged, or obsolete proteins.

8. D Feedback: Transcription forms RNA from DNA. (Translation forms a polypeptide chain from RNA; DNA replication forms new DNA; mitosis is the process of dividing the nucleus during cell replication).

9. A Feedback: Prophase involves all of the preparatory steps necessary prior to nuclear division such as condensation of chromatin to chromosomes, spindle fiber formation, disappearance of the nuclear envelope, and migration of centrioles to opposite poles.

10. B Feedback: DNA within the nucleus is required for protein synthesis and cell division.

11. [1] The plasma membrane is the outer barrier of the cell. It forms the outer, limiting barrier separating the internal contents of the cell from the external environment. [2] The nucleus is the largest structure within the cell and is enclosed by a nuclear envelope. Most of its internal content is the genetic material (DNA). [3] Cytoplasm is a general term for all cellular contents located between the plasma membrane the nucleus. Its primary components are the cytosol, organelles, and inclusions.

12. Proteins associated with the plasma membrane of a cell may function as: (1) transport proteins (including channels, carriers, pumps, symporters, and antiporters) regulating passage into or out of the cell; (2) cell surface receptors that bind ligands for cell communication; (3) identity markers that communicate to other cells that they belong in the body; (4) enzymes that catalyze chemical reactions; (5) anchoring sites for the cytoskeleton; or (6) cell adhesion proteins that bind cells together.

13. [1] Simple diffusion occurs when small nonpolar molecules are able to move through the membrane phospholipid bilayer down their concentration gradient without the need of transport molecules. [2] Facilitated diffusion involves movement of charged ions or polar molecules across the plasma membrane down their

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concentration gradient through either channels (for ions) or by carriers (for polar molecules). [3] Osmosis is a process involving the movement of water down its concentration gradient through a semipermeable membrane.

14. Active transport is a membrane transport process in which a substance is moved up its concentration gradient.

Primary active transport involves pumps (e.g., Ca2+ pumps and Na+/K+ pumps) that directly utilize the energy from the hydrolysis of ATP to move solutes against their concentration gradients to maintain concentration gradients at the plasma membrane. Secondary active transport couples the movement of one molecule down its concentration gradient (which provides the energy) to the movement of another molecule against its concentration gradient.

Symport secondary active transport is when the two substances move in the same directions, whereas antiport secondary active transport is when the two substances move in the opposite direction. Vesicular transport requires an input of energy to drive the bulk movement of molecules into or out of a cell through vesicles. Exocytosis is the release of contents within a vesicle from the cell into the interstitial fluid. Endocytosis occurs with the invagination of the plasma membrane that results in bringing material into the cell through the formation of a vesicle. The three forms of endocytosis include: phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis (bringing in specific type of molecule after it binds to plasma membrane receptors).

15. [1] The endoplasmic reticulum consists of a series of folded membranes within the cytoplasm. (a) The rough endoplasmic reticulum is studded with ribosomes and is involved in protein synthesis, the processing of the new proteins (e.g., adding carbohydrates), formation of peroxisomes, and formation of transport vesicles. (b) The smooth endoplasmic reticulum is responsible for lipid synthesis, processing molecules, the detoxification of lipid-soluble toxins, and the formation of vesicles. [2] The Golgi apparatus consists of a series of flattened membranous sacs, responsible for the synthesis of proteoglycans, modification of proteins, formation of lysosomes, and formation of secretory vesicles. [3] Lysosomes and peroxisomes are small membranous spheres containing metabolic enzymes. (a) Lysosomes contain digestive enzymes that are responsible for the breakdown of cellular structures or ingested materials. (b) Peroxisomes contain enzymes that break down molecules (e.g., fatty acids during beta oxidation) with the accompanying formation of hydrogen peroxide. They also participate in the synthesis of some specialized lipids (e.g., bile salts). [4] Mitochondria are unlike other membrane-bound organelles, because they consist of two distinct membranes, one internal to the other. They are responsible for the majority of ATP synthesis within the cell that occurs through aerobic cellular respiration.

16. (1) Microfilaments are composed of an intertwined actin protein network that lines the inner boundary of the plasma membrane. They are involved in maintaining cell shape, forming internal support of microvilli, participating in cytokinesis, changes to the cell’s shape, and they participate in muscle contraction. (2) Intermediate filaments vary in composition, depending upon the cell type, and are involved in structural support of the cell and stabilization of junctions between them. (3) Microtubules are hollow cylinders composed of long chains of a globular protein called tubulin. They are not permanent structures and may be elongated or shortened as needed. Microtubules help maintain cell shape, organize and move organelles within a cell, form protein components of cilia and flagella, participate in cellular transport of vesicles, and separate chromosomes during cell division.

17. Both cilia and microvilli are projections of the plasma membrane supported by protein. Cilia are relatively small hair-like projections that are supported by microtubule protein. They participate in moving substances past a cell's surface. In comparison, microvilli are shorter, wider, and more densely packed than cilia. They are supported by microfilament protein. Microvilli serve to increase the cell's surface area.

18. Transcription occurs within the nucleus and is the process by which DNA is converted to mRNA during gene expression. Transcription is organized into three steps: initiation, elongation, and termination. During initiation the RNA polymerase attaches to the promoter region of a gene that is to be transcribed. Elongation involves RNA polymerase enzyme assisting complementary base pairs of free ribonucleotides with the DNA with a phosphodiester bond formed between the ribonucleotides of the new RNA strand. Termination of transcription occurs as the RNA polymerase reaches the terminal region of the gene and releases the newly formed RNA strand (and DNA completely closes).

Translation (or synthesis of a protein) involves three processes: initiation, elongation, and termination. During initiation, the small subunit, large subunit, mRNA, and the first charged tRNA (tRNA with anticodon UAC and holding methionine amino acid) form a complex. This tRNA is in the P site of the ribosome. During elongation the following steps occur repeatedly: (a) a charged tRNA with its amino acid attached is positioned in the A site of the ribosome. The specific tRNA is based on complementary base pairing of the codon of the mRNA and the anticodon

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of that charged tRNA. (b) A peptide bond forms between the two amino acids (one in the P site and the other in the A site). (c) At this point the first tRNA is released and the ribosome shifts down one codon on the mRNA. The process continues until a stop codon enters the A site signaling the termination of translation. Termination occurs when a stop codon (UAA, UAG, or UGA) enters the A site to end translation. A release factor enters the A site at this point instead of a charged tRNA. When the ribosome hits the factor bound to the mRNA stop codon, the two subunits of the ribosome are separated from the mRNA and the newly synthesized protein is released.

19. DNA directly controls cell processes because it is in charge of the synthesis of all cell proteins. By regulating gene expression, the presence of metabolic enzymes, receptors, or structural proteins may be affected. Because enzymes (which are formed under the direction of DNA) are responsible for the metabolic processes of the cell (digestion and synthesis chemical reactions), thus DNA is also indirectly responsible for these processes as well.

20. The cell cycle is organized into interphase (which includes G1, S, and G2) and mitotic phase (which is divided into mitosis and cytokinesis). G1: During the G1 phase cells grow and produce new organelles and other structures needed for DNA replication. S phase: During the S phase the DNA is replicated, a process that involves DNA polymerase enzyme. DNA polymerase catalyzes DNA replication by assisting free deoxyribonucleotides to complementarily base-pair with exposed bases of the DNA strands. All 46 strands of DNA are replicated (and the replicated strands called sister chromatids remain attached at centromeres). G2: During the G2 phase, centriole replication is completed (having produced two centriole pairs present within the cell) and enzymes and other structures needed for cell division are synthesized.

The mitotic phase consists of two overlapping events. Mitosis is nuclear division that results in the formation of two nuclei within the cell whereas cytokinesis is the dividing of the cytoplasm and plasma membrane resulting in splitting the cell into two daughter cells—each with their own nucleus.

The four stages in mitosis include: [1] Prophase: chromatin supercoils into chromosomes, the nucleolus breaks down and disappears, spindle fibers begin to grow from centrioles, centriole pairs move to opposite poles of the cell, and the nuclear envelope disassembles; [2] Metaphase: chromosomes are aligned in the equatorial plate as spindle fibers attach to the centromere of each chromosome and move them into the center of the cell; [3] Anaphase: spindle fibers move sister chromatids apart toward the cell’s poles (and each sister chromatid, with its own centromere, is now considered a chromosome); and [4] Telophase: chromosomes arrive at each cell pole, chromosomes uncoil, each new nucleus forms a nucleolus, the mitotic spindle breaks up and disappears, and a new nuclear envelope forms around each of the two sets of chromatin.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: Lysosomes are small membranous sacs containing digestive enzymes that are responsible for digestion of unneeded or unwanted substances.

2. B Feedback: Receptor-mediated endocytosis is required to remove LDL particles from the blood.

3. D Feedback: Cancer involves uncontrolled cell division (or mitosis).

4. C Feedback: Testosterone is a hormone that requires a receptor to initiate metabolic events within the cell.

5. A Feedback: Protein synthesis is a two-step process: first transcription, then translation.

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Answers to “Can You Synthesize What You’ve Learned?”

1. An inability to produce albumin would affect the osmolality of the blood, decreasing the osmotic pressure. Less albumin in the blood impairs the ability to "pull" fluid from the interstitial spaces back into the blood. Excess fluid remains in the interstitial space causing edema.

2. Pneumonia results in lower levels of oxygen in the blood. Thus, the concentration gradient for oxygen between the blood and cells decreases. Consequently, there is less diffusion of oxygen out of the blood into tissues.

3. The removal of LDL particles from the blood into cells is accomplished by receptor-mediated endocytosis, the mechanism dependent upon the presence of receptor proteins. A mutation in the gene coding for the receptor(s) responsible for the endocytosis of LDL would result in less being endocytosed by his cells, and more remaining in his blood.

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Chapter 5 Answers to “What Did You Learn?”

1.

Many epithelial tissues are exposed to damage and abrasion, and therefore need to be replaced frequently.

2. Epithelial cells line all of the membranes where substances may enter the body. They must therefore have the capacity to regulate what may pass through the membranes.

3.

Simple epithelium consists of a single layer of cells. Stratified epithelium consists of two or more layers.

4.

Simple squamous epithelium lines the air sacs of the lungs.

5.

Keratinized stratified squamous epithelium is the correct tissue.

6.

Multicellular exocrine glands consist of a duct and either a tubular or an acinar secretory section.

7. The cells of a merocrine gland secrete their products by exocytosis. The cells of a holocrine gland will rupture completely in order to release their contents.

8. Resident cells are fixed in position within the connective tissue. Wandering cells are components of the immune system and move through the tissue, providing for repair and for protection from infection.

9. Glycosaminoglycans (GAG) are large extracellular carbohydrates that absorb water within the ground substance of a connective tissue, thereby regulating the viscosity of the solution.

10. Connective tissues such as bone and cartilage support the entire body and act as sites for muscle attachments.

Cartilage maintains the integrity and shape of structures such as the trachea and nasal septum. Outer layers of collagen surround and support nearly all of the organs in the body.

11. Mesenchyme is an embryonic tissue composed of stellate and spindle-shaped cells surrounded by a ground substance. It is the embryonic origin of all adult connective tissues.

12. Loose connective tissue consists predominantly of ground substance with few fibers. Dense connective tissues have very little ground substance, and consist largely of a dense arrangement of fibers.

13. Fibrocartilage may be well suited for resisting compression forces and/or bearing weight. It contains very little ground substance; it does however have numerous collagen fibers. It does not have a perichondrium.

14. Blood is derived from mesenchyme like all other connective tissues. It contains a very fluid ground substance called plasma, numerous dissolved proteins, and formed cellular elements.

15. Cardiac and skeletal muscles are both striated and contain similar arrangements of intracellular contractile proteins. Whereas cardiac muscle consists of individual branching cells, skeletal muscle consists of large multinucleated cells. Cardiac muscle is voluntary; skeletal muscle is involuntary.

16. Neurons are specialized for transmitting nervous impulses. Glial cells do not transmit the nervous impulse; however, they serve numerous critical support functions in the nervous system.

17. The stomach is an organ that contains all four tissue types. It is lined with epithelium, it has numerous layers of smooth muscle, it is highly innervated, and it contains several types of connective tissue.

18.

The parietal layer lines the inside of the body wall. The deeper visceral layer lines organs.

19. The three primary germ layers – the ectoderm, endoderm, and mesoderm – form by the third week of embryonic development.

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20. A metaplasia occurs when a mature epithelium type changes to another type of mature epithelium. For example, the trachea epithelium of smokers may undergo a metaplastic change from the normal pseudostratified ciliated columnar epithelium to a nonkeratinized stratified squamous epithelium. Dysplasia refers to abnormal tissue development. Dysplasias have the potential to turn into cancer (and thus are sometimes referred to as precancerous), but they also have the potential to revert back to normal tissue. A neoplasia refers to tissue growth that is out of control, and a malignant neoplasia is characterized by its potential to invade local tissues and metastasize to other sites in the body.

21. Epithelial tissues become thinner with age. The amount of collagen also decreases with age, affecting the pliability and resilience of connective tissues.

Answers to “Do You Know the Basics?”

1. D Feedback: Bone connective tissue is composed predominantly of mineralized calcium, which serves as the structural component of bones.

2. C Feedback: Areolar connective tissue is a loose connective tissue. It does not contain tightly packed fibers.

3. A Feedback: Mucous membranes line body cavities that are exposed to the outside of the body, such as in the respiratory, digestive, urinary, and reproductive systems.

4. A Feedback: Because simple squamous epithelium consists of only a single layer of epithelial cells, all of the cells are in direct contact with the basement membrane.

5. D Feedback: Epithelial tissue is avascular. It does not contain blood vessels.

6. C Feedback: All cartilage contains chondrocytes. Hyaline and elastic cartilages are surrounded by perichondrium.

7. C Feedback: Smooth muscle is derived from mesoderm.

8.B Feedback: Striated skeletal muscle cells fuse during embryonic development, and are therefore multinucleated.

9.B Feedback: The trachea is lined with pseudostratified ciliated columnar epithelium.

10. A Feedback: Merocrine glands secrete their products by exocytosis.

11. Epithelial tissues are composed primarily of cells without a lot of extracellular matrix. Because of their role in lining surfaces they possess polarity; they lack blood vessels; they are highly innervated; and they often have a high capacity for regeneration. Epithelial tissue is supported by a basement membrane, an underlying layer of connective tissue.

12. Epithelia are classified according to the number of layers in the tissue. Simple epithelium has only one layer. Stratified epithelium has two or more layers. Epithelium is also categorized based on the shape of cells: squamous, cuboidal, or columnar.

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13. The lumen of the stomach is lined with simple columnar epithelium. The oral cavity is lined with stratified squamous epithelium. The urinary bladder is lined with transitional epithelium. The alveoli of the lungs are lined with simple squamous epithelium.

14. The cells of a merocrine gland secrete their products by exocytosis. Apocrine gland cells pinch off the entire apical domain of the plasma membrane. The entire cell of a holocrine gland ruptures in order to release its contents.

15. The skin is the cutaneous membrane. Mucous membranes line body cavities exposed to the outside of the body, whereas serous membranes line body cavities not exposed to the outside of the body. Synovial membranes produce synovial fluid within joints.

16. All connective tissues are derived from mesenchyme and have some proportion of ground substance, an extracellular matrix with various arrangements of large extracellular fibers.

17. Dense regular connective tissues have fibers arranged parallel to each other, whereas the fibers of dense irregular connective tissues are arranged in clumps that extend in various directions.

18. Hyaline cartilage is the most abundant type of cartilage, found at the ends of long bones, within rings of hyaline cartilage in the trachea, costal cartilage, and nasal septum. In these regions, hyaline cartilage provides for support, but is more flexible than bone. Elastic cartilage is located within the ear and epiglottis, where recoil and flexibility is important. Fibrocartilage is optimized at resisting compression forces and is therefore found within intervertebral disks of the spinal column, menisci of the knees, and the pubic symphysis in between the two hip bones.

19. Skeletal muscle is voluntary; smooth and cardiac muscle are involuntary. Skeletal and cardiac muscle are striated, whereas smooth muscle is not. Skeletal muscle is primarily attached to bones, smooth muscle is present within the walls of hollow organs, and cardiac muscle is located only within the walls of the heart.

20. Neurons are specialized for transmitting nervous impulses. Glial cells do not transmit the nervous impulse; however, they serve numerous critical support functions in the nervous system.

Answers to “Can You Apply What You’ve Learned?”

1.C Feedback: Bursae contain synovial membranes.

2. C Feedback: The iris of the eye contains involuntary smooth muscle.

3.B Feedback: The mucous membrane within the cheek is lined with stratified squamous epithelium, which is well adapted for dealing with abrasion.

4.A Feedback: The mucous membrane within the cheek is lined with stratified squamous epithelium.

5.B Feedback: Although the deeper layers of stratified squamous epithelium are cuboidal, the tissue is named after the apical layers.

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Answers to “Can You Synthesize What You’ve Learned?”

1. The student is looking at areolar connective tissue. Areolar connective tissue is found in the papillary layer of the dermis, as well as the subcutaneous layer of the skin. It also surrounds organs, nerve cells, some muscle cells, and blood vessels.

2. The articular cartilage at the ends of long bones consists of hyaline cartilage. Chondroitin sulfate is a component of the hyaline cartilage matrix. Therefore the supplement may help reduce the effects of arthritis in the joint, if that is indeed the cause of the pain.

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Chapter 6 Answers to “What Did You Learn?”

1. The thorn would first penetrate the stratum corneum, the most superficial layer of the epidermis. It would then puncture the stratum lucidum, the stratum granulosum, the stratum spinosum, and finally the stratum basale.

2. Keratinization occurs due to the production of keratin, a hardening agent, within keratinocytes. Within the stratum spinosum, the cells fill up with keratin, and the nucleus and organelles become polymerized within the protein, eventually killing the cell. The cells then rupture, releasing keratin at the stratum granulosum. The subsequent superficial layers of the stratum lucidum and corneum consist of ruptured keratinocytes embedded in keratin. This provides for a hardened waterproof barrier between the external environment and the dermis below.

3. Hemoglobin turns red when bound to oxygen. As blood vessels bring hemoglobin close to the surface within the dermis, the skin takes on a reddish hue.

4. Friction ridges increase friction on contact with the skin. It has been hypothesized that they may also provide for pliability at the surface of the skin.

5. The papillary layer, composed primarily of areolar connective tissue, is the most superficial layer of the dermis.

The reticular layer lies deep to the papillary layer, makes up the majority of the thickness of the skin, and is predominantly dense irregular connective tissue. Dermal papillae, the folds within the papillary layer, contain numerous capillaries and tactile receptors. The reticular layer contains most of the structures associated with the dermis, such as the hair follicles, sebaceous and sweat glands, nerves, and blood vessels.

6. Tension lines correspond to the direction of collagen bundles within the dermis of the skin. They are relevant clinically as these represent the optimum direction for an incision through the skin. An incision perpendicular to the tension lines can be easily pulled apart and is more likely to result in scarring.

7.

The subcutaneous layer, deep to the skin, consists predominantly of areolar and adipose tissues.

8. Vitamin D3, also called cholecalciferol, is synthesized from a steroid precursor by the keratinocytes when they are exposed to ultraviolet radiation.

9. The skin is water resistant, but not entirely waterproof. Some water is always lost through the skin when you sweat. More water is typically lost through transpiration, a process in which fluids slowly penetrate through the epidermis and then evaporate into the surrounding air.

10. The skin can dissipate heat by vasodilating the blood vessels in the dermis. This allows for more warm blood to travel close to the body surface, and the heat from the blood to dissipate through the skin. In addition, sweating allows fluid to be released on the surface of the skin, and when that fluid evaporates, it cools the body.

11. The hyponychium is a thick layer of stratum corneum, deep to the free edge of the nail. The eponychium, or cuticle, is a small fold of skin that covers the proximal edge of the body of the nail.

12.

The three zones of hair are the hair bulb, the root, and the shaft.

13. Hair on the scalp protects from exposure to the sun. Hairs within the nostrils, ears, or eyelashes protect the respective openings from debris. The eyebrows help to keep sweat out of the eyes. On a cold day the hair on the scalp also acts as insulation, preventing the loss of body heat.

14. Merocrine sweat glands are distributed throughout the body, whereas apocrine glands are primarily associated with hair follicles in the axillary, genital, and anal regions. Sweat produced by merocrine glands contains over 99% water with salts and trace amounts of metabolic waste. Its primary function is thermoregulation by evaporative cooling. Sweat from apocrine glands, along with water and salts, also contains an abundance of proteins and lipids.

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15.

Sebaceous glands secrete an oily substance called sebum into the hair follicles and onto the hair shaft.

16. Granulation tissue occurs as the wound is actively rebuilding blood supply to the damaged region, prior to formation of new collagen or epithelium. It consists of developing capillaries and fibrocytes.

17.

The epidermis is derived from ectoderm, whereas the dermis develops from the deeper mesoderm.

18. Chronic overexposure to UV light can damage the DNA of epidermal stem cells, inhibiting their ability to repair the skin.

Answers to “Do You Know the Basics?”

1. B Feedback: Sebaceous glands are holocrine glands.

2. D Feedback: Within the stratum granulosum of the epidermis, keratinocytes accumulate keratin inside their cytoplasm and eventually die, resulting in keratinization of the skin.

3. B Feedback: Sweat produced from merocrine glands consists primarily of water. In contrast, apocrine gland secretions also contain lipids and proteins, and sebaceous glands produce an oily substance called sebum.

4. B Feedback: Calcium is not stored within the dermis. However, the skin does act as a barrier separating the body from the external environment; it does participate in thermoregulation; and it does contain components of the immune system.

5. A Feedback: The papillary layer of the dermis is composed of areolar connective tissue.

6. B Feedback: It is a pigment that accumulates in keratinocytes.

7. B Feedback: Similar to a first-degree burn, a second-degree burn involves the epidermis. However, a second-degree burn also includes damage to part of the dermis. A third-degree burn would include damage through all of the layers of the epidermis and dermis, as well as the deeper subcutaneous layer.

8. B Feedback: Cell division occurs within the matrix of the bulb. These cells are then pushed up, forming the medulla and cortex of the hair.

9. C Feedback: Tactile cell receptors within the dermal papillae detect touch sensations.

10. D Feedback: Granular tissue occurs as the wound is actively rebuilding blood supply to the damaged region, following the formation of a blood clot, but prior to the formation of new collagen or epithelium.

11. The stratum basale, spinosum, and granulosum contain living cells. The stratum lucidum (if present) and stratum corneum are composed of dead keratinocytes.

12. The stratum basale contains adult stem cells responsible for regenerating the tissue, tactile cells called Merkel

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cells, and melanocytes responsible for production of melanin, a UV absorbing pigment. The stratum spinosum mostly contains keratinocytes which are actively producing keratin, along with a few Langerhans cells which fight infection in the epidermis. The stratum corneum contains keratinocytes, impacted with keratin. Finally, the most superficial layers, the stratum lucidum (present only in thick skin) and corneum, contain dead keratinocytes imbedded within keratin.

13. The papillary layer, composed primarily of areolar connective tissue, is the most superficial layer of the dermis.

The reticular layer lies deep to the papillary layer, makes up the majority of the thickness of the skin, and is predominantly dense irregular connective tissue. Dermal papillae, the folds within the papillary layer, contain numerous capillaries and tactile receptors. The reticular layer contains most of the structures associated with the dermis, such as the hair follicles, sebaceous and sweat glands, nerves, and blood vessels.

14. Keratinocytes produce vitamin D3, a precursor to vitamin D, when exposed to UV light. Further modification within first the liver and then the kidneys yields the active form of vitamin D. 15. The nail body represents the majority of the nail structure, and is composed of highly keratinized epithelium.

The living portion of the epidermis, deep to the nail body, is the nail bed. The eponychium, or cuticle, is a small fold of skin that covers the proximal edge of the nail body. The lunula is a whitish portion of the nail body, produced by a thick stratum basale within the underlying epidermis.

16. Lanugo is a fine unpigmented hair produced during the last trimester of fetal development. Vellus hair is the primary hair on humans and is found distributed through the body. Terminal hair is coarser than vellus hair and is located on the scalp, eyebrows, and eyelashes. After puberty it is also present in the axillary and pubic regions.

17. Ceruminous glands are located within the external acoustic meatus, where they secrete the waterproof wax that lines the canal.

18. The initial stages in repair of the integument involve the introduction into the area of clotting proteins, white blood cells, and antibodies from damaged blood vessels. The clotting factors patch the wound together and block the entry of pathogens into the body. As new vessels grow they form a granular tissue, which is followed by the production of new collagen fibers within the dermis. Growth of epithelium is the last step in wound repair.

19.

The epidermis is derived from ectoderm, whereas the dermis develops from the deeper mesoderm.

20. With time, stem cells required to regenerate integument become less active, making it more difficult to repair aging tissues. Consequently, the amount of collagen deceases, and elastic fibers lose elasticity, allowing the skin to wrinkle. The activity of hair follicles also decreases, causing thinning of the hair.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: Acne is an infection of sebaceous glands by bacteria feeding off of sebum. Sebum production increases during puberty.

2. C Feedback: The stratum corneum of the epidermis is composed of flattened anucleate cells.

3. C Feedback: Since the epidermis is avascular, a wound that involves bleeding must permeate the dermis. Since the wound does not appear deep, it did not damage the entire depth of the dermis.

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Answers to “Can You Synthesize What You’ve Learned?”

1. On a cold day, vasoconstriction of dermal blood vessels shunts blood away from the surface of the skin in an effort to retain heat. Deprived of blood supply, the surface of the skin may appear pale. When entering back into a warm room, vasodilation allows more blood to reach the surface of the skin, causing a flushed appearance.

2. Third degree burns involve the epidermis, dermis and subcutaneous layer. The main complications are dehydration (because the entire portion of skin has been lost, and water cannot be retained in that area) and infection (again, because the entire portion of skin has been lost). Teri’s physician likely would give her antibiotics to help prevent or reduce infection, and her fluids will be replaced to treat the dehydration. She also may be given a skin graft, which not only would help replace the lost skin, but may help minimize the complications from infection and dehydration.

3. Based on the description of the mole and the fact that a preexisting mole appears to have changed appearance, it appears John has a malignant melanoma. A malignant melanoma may be described using the ABCDE rule: it typically is Asymmetrical, its Borders are irregular, its Color is not uniform (but may be darker brown or black), its Diameter is larger than 6 mm, and it is Evolving in that it changed shape and appearance over time. Unfortunately, this is the most deadly type of skin cancer and John should be very concerned. The dermatologist will excise the mole, examine it under the microscope, and then determine if further treatment or action is needed.

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Chapter 7 Answers to “What Did You Learn?”

1. Compact bone consists of a solid, dense mass of bone tissue, whereas spongy bone contains a more porous arrangement of the tissue.

2.

Fibrocartilage is located within intervertebral discs, the pubic symphysis, and the menisci of the knee.

3. Bones serve as a reservoir for calcium and phosphate. Calcium is an important component in muscle contraction, nerve conduction, and blood clotting. Phosphate is required for the production of ATP and nucleotides.

4.

Most of the bones of the roof of the skull, the scapulae, the sternum, and the ribs are flat bones.

5. The diaphysis is the shaft of a long bone. It consists of a relatively thick cylindrical arrangement of compact bone, lined with spicules of spongy bone, usually surrounding a central medullary cavity. The epiphyses are the knobby ends of long bones. They consist primarily of spongy bone, surrounded by a thin crust of compact bone.

6.

The nutrient foramen is an opening within a bone for the nutrient artery and vein as well as innervation.

7. The adult skeleton contains red bone marrow within spongy bone of flat bones in the skull, vertebrae, ribs, sternum, and ossa coxae.

8. Osteoprogenitor cells are the adult stem cells from which the remaining cells of bone tissue are produced.

Osteoblasts produce osteoid, which gives rise to the matrix of bone tissue. Osteocytes are differentiated osteoblasts that have become trapped within and continue to maintain their matrix. Osteoclasts participate in bone resorption, breaking down bone tissue and releasing calcium and phosphate.

9. The matrix of bone tissue consists primarily of organic collagen fibers surrounded by inorganic hydroxyapatite crystals (precipitated calcium phosphate).

10. An osteon consists of several rings of bone tissue, called lamellae, surrounding a central canal. Osteocytes, each surrounded by a small cavity called a lacuna, are located in between the lamellae. Canaliculi run transversely through the lamellae, bridging the lacunae of osteocytes, permitting them to form connections through the crystalline matrix.

11. The matrix of hyaline cartilage does not contain calcium, but does contain a large percentage of water, nearly 80%. Also, unlike bone tissue, mature hyaline cartilage is avascular and does not contain nerves.

12. Appositional growth of cartilage occurs at the periphery of the tissue, along the perichondrium. Interstitial growth occurs from within the matrix.

13. Intramembranous ossification begins during the eighth week of fetal development and produces the flat bones of the skull and face, as well as the clavicles.

14. Endochondral ossification starts with the formation of a periosteal bony collar around embryonic hyaline cartilage. A periosteal bud extends from the periosteum into the cartilage shaft, forming the primary ossification center. Secondary ossification centers then form at the epiphyses of the developing bone. Eventually, bone tissue replaces all of the cartilage except at the epiphyseal growth plates and the articular cartilage. Around the time of puberty the epiphyseal plates are replaced completely by bone tissue.

15. Bones are widened through appositional growth at the periosteum by osteoblasts laying down rings of matrix called circumferential lamellae.

16.

Bone remodeling is the removal of old bone tissue and its replacement by new bone tissue. It occurs

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primarily in response to mechanical stress upon the bone or to stimuli from hormones such as growth hormone, thyroid hormone, or sex hormones.

17. Growth hormone stimulates the growth of epiphyseal plates, thereby causing interstitial growth. Thyroid hormone affects the basal metabolic growth rate of bone cells.

18. UV light absorbed through the skin converts 7-dehydrocholesterol in the blood to vitamin D3. Vitamin D3 is then converted to calcidiol within the liver and then to calcitriol (the active form of vitamin D) in the kidneys.

19. Parathyroid hormone is secreted from the parathyroid glands in response to low levels of calcium in the blood. Parathyroid hormone activates the conversion of calcidiol to calcitriol in the kidneys. Parathyroid hormone and calcitriol act synergistically to increase the release of calcium from bone tissue and to increase the retention of calcium within the kidneys. Calcitriol also facilitates the absorption of calcium from the small intestine.

20. Calcitonin decreases blood calcium levels by decreasing osteoclast activity in the skeleton, thereby inhibiting bone resorption. It also inhibits the reabsorption of calcium from the kidneys, thereby eliminating it in urine.

21. Estrogen is involved in protection of women from osteoporosis. As estrogen levels drop in postmenopausal women, they are more likely to experience osteoporosis.

22. Initially, broken blood vessels in a broken bone form a hematoma. The hematoma is replaced by a fibrocartilaginous callus, which is then replaced by a compact bone, and then finally remodeled.

23. A fibrocartilaginous callus consists of dense irregular connective tissue, which although strong is unlike bone tissue in that it is not capable of bearing weight and can be damaged when pressure is applied.

Answers to “Do You Know the Basics?”

1. D Feedback: The flat bones of the skull, such as the frontal bone, are formed from intramembranous bone growth.

2. A Feedback: Red bone marrow serves as the site of hemopoiesis, and not cartilage.

3. D Feedback: The red bone marrow (and not the yellow bone marrow) forms blood cells.

4. C Feedback: The femur, with a diaphysis, medullary cavity, and distinct epiphyses is a long bone.

5. C Feedback: Osteoclasts resorb bone matrix, so these cells are most likely to have formed the medullary cavity (the space) within the shaft of a long bone.

6. C Feedback: Periosteum is responsible for growth in bone width.

7. B Feedback: Canaliculi allow osteocytes to exchange nutrients and wastes.

8. A Feedback: The matrix of hyaline cartilage is very similar to that of bone, except it does not contain calcium.

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9. A Feedback: Calcitonin is secreted by the thyroid gland. Calcitonin reduces blood calcium levels, by increasing osteoblast activity and decreasing osteoclast activity.

10. A Feedback: Epiphyseal growth plates are replaced by a line of compact bone called the epiphyseal line.

11. The diaphysis is the shaft of a long bone. It consists of a relatively thick cylindrical arrangement of compact bone, lined with spicules of spongy bone, usually surrounding a central medullary cavity. The epiphyses are the knobby ends of long bones. They consist primarily of spongy bone, surrounded by a thin crust of compact bone. A typical long bone consists of a diaphysis separated from one or more epiphyses by either epiphyseal plates of hyaline cartilage, or by epiphyseal lines composed of compact bone. The entire structure is surrounded by dense irregular connective tissue, the periosteum, except at the articular ends where it is covered with hyaline cartilage.

12. Osteoblasts produce osteoid which gives rise to the matrix of bone tissue. They are responsible for the appositional growth of bones. Osteoclasts participate in bone resorption, breaking down bone tissue and releasing calcium and phosphate. Together, osteoblasts and osteoclasts participate in bone remodeling.

13. The osteon is the structural unit of compact bone. It consists of several rings of bone tissue, called lamellae, surrounding a central canal. Osteocytes, each surrounded by a small cavity called a lacuna, are located in between the lamellae. Canaliculi run transversely through the lamellae, bridging the lacunae of osteocytes, permitting them to form connections through the crystalline matrix.

14. Appositional growth of cartilage occurs at the periphery of the tissue, along the perichondrium. Interstitial growth occurs from within the matrix.

15. Endochondral ossification starts with the formation of a periosteal bony collar around embryonic hyaline cartilage. A periosteal bud extends from the periosteum into the cartilage shaft, forming the primary ossification center. Secondary ossification centers then form at the epiphyses of the developing bone. Eventually bone tissue replaces all of the cartilage except at the epiphyseal growth plates and the articular cartilage. Around the time of puberty the epiphyseal plates are replaced completely by bone tissue.

16. Growth at epiphyseal plates occurs primarily within the proliferating zone, as chondrocytes divide, and within the hypertrophic zone as the chondrocytes expand.

17. Mechanical stress such as that experienced during weight-bearing exercise induces bone remodeling, consequently contributing to bone mass.

18. Growth hormone stimulates the liver to produce IGF, which stimulates cartilage growth at the epiphyseal plate. In contrast, high levels of glucocorticoids increase bone loss and can impair bone growth in children.

19. Parathyroid hormone is secreted from the parathyroid glands in response to low levels of calcium in the blood. Parathyroid hormone activates the conversion of calcidiol to calcitriol in the kidneys. Parathyroid hormone and calcitriol act synergistically to increase the release of calcium from bone tissue and to increase the retention of calcium within the kidneys.

20. Initially, broken blood vessels in a broken bone form a hematoma. The hematoma is replaced by a fibrocartilaginous callus, which is then replaced by a compact bone, and then finally remodeled.

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Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: Red bone marrow contains active hematopoietic cells, which are needed to treat leukemia. In adults, the red marrow is only located within the spongy bone of flat bones, such as the hip.

2. C Feedback: Collagen, a protein, is destroyed with excessive heat, leaving bone tissue dry and brittle.

Hypoxyapatite crystals dissolve in acid, leaving behind flexible collagen fibers.

3. B Feedback: Yellow marrow found within the medullary cavity of long bones is rich in adipose tissue.

4. A Feedback: The fusion of the epiphyses to the diaphysis occurs in response to hormones produced at puberty, thus providing an indication as to the age of the skeleton.

5. C Feedback: Chondrocytes form attacks within the zone of proliferation. These then become enlarged within the zone of hypertrophy.

Answers to “Can You Synthesize What You’ve Learned?”

1. Removal of the parathyroid glands would prevent the person from responding to decreases in blood calcium and prevent the release of parathyroid hormone. Maintaining the parathyroid glands after the removal of the thyroid gland would significantly improve the person’s ability to regulate blood calcium levels.

2. Mechanical stress such as that experienced during weight-bearing exercise induces bone growth, consequently contributing to bone mass. When bones are immobilized to facilitate repair they are not experiencing stress.

Consequently, the amount of bone resorption exceeds the amount of interstitial and appositional growth, thereby weakening the bone.

3. Elise’s history indicates numerous factors that can contribute to decreased bone mass and subsequent difficulty in bone repair. Due to a lack of activity and physical interactions with other children her developing bones may have experienced less mechanical stress during a formative developmental period, severely affecting bone mass.

Spending most of her time indoors, she may have a deficiency in vitamin D, because of her limited exposure to UV light. Consumption of soft drinks also decreases bone density, in concert with the other factors, leaving her susceptible to damage and prolonged repair.

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Chapter 8 Answers to “What Did You Learn?”

1. The axial skeleton primarily serves to provide a framework for and protection of internal organs, as well as hemopoiesis. It consists of the skull, vertebral column, and thoracic cage.

2.

Foramina and fissures are both openings. A foramen is rounded whereas a fissure is elongated.

3. The cranium of the skull consists of the frontal, parietal, occipital, ethmoid, sphenoid, and temporal bones. The zygomatic, lacrimal, nasal, inferior nasal conchae, maxillae, vomer, mandible, and palatine bones comprise the face.

4. The frontal bones, maxillae, nasal bones, zygomatic bones, and mandible are the predominant bones visible from the anterior of the skull.

5. The sphenoid and temporal bones comprise the middle cranial fossa, which houses the temporal lobes of the brain and the pituitary gland.

6. The lambdoid suture is the articulation between the occipital and parietal bones. It is the last cranial suture to fuse, usually by age 40.

7.

The palatine, maxillae, and zygomatic bones form the floor of the orbit of the eye.

8.

The maxillary, sphenoid, ethmoid, and frontal bones contain the paranasal sinuses.

9.

The malleus, incus, and stapes are auditory ossicles located within the petrous portion of the temporal bone.

10. Generally, male skulls have a more predominant superciliary arch and a more sloping frontal bone than female skulls. The female skull will likely have a sharper supraorbital margin, a more triangular mental protuberance, a smoother, less prominent occipital protuberance, and a more obtuse mandibular angle.

11.

The posterior and anterior are the largest of the fontanelles, closing by 9 and 15 months of age, respectively.

12.

The five lumbar vertebrae comprise the “small” of the back.

13.

The cervical and lumbar curvatures of the spine are secondary curvatures that appear after birth.

14. Transverse foramina, which contain the vertebral artery and vein, are located in the transverse processes of cervical vertebrae. The vertebral foramen is located posterior to the body of a vertebra and contains the spinal cord and meninges. The intervertebral foramina are located in between the pedicles of consecutive vertebra and allow for passage of spinal nerve roots joining the spinal cord.

15. The atlas lacks a body and elongated superior articular facets for articulation with the occipital condyles of the skull. The axis has a superior projection called the dens which serves as a pivot point for the atlas.

16. The sternal angle is the articulation between the manubrium and the body of the sternum. It is located at the level of the articulation of the second rib with the sternum.

17. The head of the rib articulates with costal facets on the bodies of consecutive vertebrae. The tubercle of the rib articulates with the transverse costal facet of the inferior vertebra.

18. The lower limbs are well suited for supporting weight and propulsion when walking. In contrast, the upper limbs are suited for dexterous activities such as grasping objects and handling tools.

19.

The sternal end of the clavicle is pyramidal in shape, whereas the acromial end is broader and flatter.

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20. The supraspinous fossa contains the supraspinatus muscle, the infraspinous fossa contains the infraspinatus muscle, and the subscapular fossa contains the subscapularis muscle.

21. The anatomical neck of the humerus is located in between the head and tubercles. The surgical neck is located distal to the anatomical neck at the site of the former epiphyseal plate, at the start of the diaphysis of the bone.

22. The capitulum articulates with the head of the radius and the trochlea articulates with the trochlear notch of the ulna.

23.

The radius and ulna both have an interosseous border from which extends the interosseous membrane.

24.

When pronated, the distal portion of the radius is crossed over the ulna and the hand faces posteriorly.

25. The carpus is composed of the trapezium, trapezoid, capitate, hamate, scaphoid, lunate, triquetrum, and pisiform bones. The scaphoid is the most common carpal bone to be broken, which may lead to damage of blood vessels and subsequent avascular necrosis of the bone.

26.

The ilium, ischium, and pubis fuse to form the os coxae.

27. The ischial tuberosities are located on the posterolateral border of the ischium. They are also called the “sits bone” because they support the weight of the body when sitting.

28.

The pelvic inlet is the superior opening into the pelvis, whereas the pelvic outlet is the inferior opening.

29. The female pelvis is usually longer and more triangular, has a more convex subpubic angle, and has a wider and shallower sciatic notch. Generally, the female pelvis is shallower and wider, allowing for the passing of an infant’s head through the birth canal.

30. The symphysial surface of a young adult is billowed and lacks a well-formed rim. With age, the rim becomes pronounced and the surface concave. With advanced age, however, the rim begins to break down.

31. The greater trochanter is located lateral to the neck and shaft of the femur. The lesser trochanter is located on the femur’s posterolateral surface. Both trochanters serve as sites of attachment of the gluteal muscles.

32.

The articular surface of the patella articulates with the patellar surface of the femur.

33.

The tibia and fibula both have an interosseous border from which extends the interosseous membrane.

34.

The tibia transduces the weight of the body to the foot. It is the only weight-bearing bone of the crural region.

35. The tarsals consist of the calcaneus, talus, navicular, cuboid, medial cuneiform, lateral cuneiform, and intermediate cuneiform bones.

36. The arches of the foot help to support the weight of the body, as well as ensure adequate blood supply and innervation to the foot.

37. Embryonic hand and foot plates develop longitudinal thickenings called digital rays, which are eventually removed by apoptosis leaving behind distinct digits.

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Answers to “Do You Know the Basics?”

1. A Feedback: Both the ethmoid bone and the vomer contribute to the bony portion of the nasal septum.

2. C Feedback: A tubercle is a small, round (bony) projection.

3. A Feedback: The coronal suture connects the frontal bone to the paired parietal bones.

4. B Feedback: Fontanelles do not fuse until well after birth, thereby permitting movement of the cranial bones during childbirth, facilitating the process.

5. B Feedback: The bodies of cervical and lumbar vertebrae are kidney shaped. The bodies of thoracic vertebrae are heart shaped.

6. B Feedback: The female subpubic angle is usually greater than 100 degrees.

7. B Feedback: The pollex (thumb) is positioned laterally when the forearm is supinated.

8. C Feedback: The supraspinous and infraspinous fossae are located on either side of the spine of the scapula.

9. B Feedback: Both the medial and lateral condyles of the femur articulate with the tibia, forming part of the architecture of the knee joint.

10. B Feedback: The ischial tuberosities are located on the posterolateral border of the ischium. They are also called the “sits bone” because they support the weight of the body when sitting.

11. Sutures are immovable joints between the bones of the skull. Because they do not fully fuse until adulthood, they permit growth and expansion of the skull during development.

12. When viewing the inferior surface of the skull, the following cranial bones may be seen easily: occipital bone, temporal bones, sphenoid, zygomatic bones, maxilla bones, palatine bones, and the vomer. In addition, a small portion of the parietal bones sometimes may be seen.

13. Aside from lightening the skull, the paranasal sinuses complement the functions of the nasal cavity by humidifying and warming inspired air.

14. The spinal curvatures are designed to better support the weight of the body than a straight spine would. Two primary curves are present at birth: thoracic and sacral curvatures. The secondary curves appear after birth; the cervical curvature appears around 3–4 months of age (when a baby is first able to hold its head upright) and the lumbar curvature appears around 1 year of age, when the baby first learns to walk.

15. True ribs (ribs 1–7) articulate with the sternum through individual costal cartilage attachments. The costal cartilage of ribs 8–10 attach to the cartilage of rib 7 and are therefore considered false ribs. Ribs 11 and 12 do not articulate with the sternum. They are also considered false ribs because they lack a direct attachment. Also appropriately, they are referred to as floating ribs.

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16. The pelvic girdle consists of the os coxae, articulating with the sternum posteriorly and together at the pubic symphysis anteriorly. The pectoral girdle consists of the scapula and clavicle. Each girdle has a socket for either the head of the humerus or the head of the femur, forming multiaxial ball-and-socket joints.

17. Both the upper and lower limbs are held in place by a girdle (pectoral girdle for the upper limbs, and pelvic girdle for the lower limbs). The proximal part of each limb consists of a single long bone while the distal part of the limb contains two bones in the forearm and leg. The hand and the foot consist of tarsals or carpals, 5 metacarpals or metatarsals, and 14 phalanges.

18. The true pelvis lies inferior to the pelvic brim, and is completely enclosed by the bones of the pelvis. The false pelvis is located above the pelvic brim, below the ala of the ilium.

19. The arches of the foot help to support the weight of the body, as well as ensure adequate blood supply and innervation to the foot.

20. The limb buds form from the lateral plate of the mesoderm, and are covered by endoderm. The upper limb buds appear about 4 weeks into fetal development, followed by the lower buds a few days later. Formation of an apical ectodermal ridge signals underlying tissues to develop. At 6 weeks of development hand and foot plates form, and future digits are delineated by digital rays. The tissue in between the digital rays is removed by apoptosis at about 8 weeks of fetal development, leaving behind distinct digits.

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: Although both the humerus and femur have a rounded head, the femur has an elongated neck but the humerus does not.

2. A Feedback: The clavicle is S-shaped. It is the site of articulation of the arm with the axial skeleton and may be damaged during a fall.

3. B Feedback: Generally, male skulls have a more predominant superciliary arch and a more sloping frontal bone than female skulls. Whereas the female skull will likely have a sharper supraorbital margin, a more triangular mental protuberance, a smoother, less prominent occipital protuberance, as well as a more obtuse mandibular angle.

4. B Feedback: The female pelvis usually has a longer, more triangular pelvis, a more convex subpubic angle, and a wider and shallower sciatic notch. Generally, the female pelvis is shallower and wider allowing for passing of an infant’s head through the birth canal.

5. C Feedback: From the presence of permanent teeth and fused epiphyseal plates you could predict the victim’s age to be well past puberty. However, the lack of ossified sutures in the skull or of a pronounced rim around the pubic symphysis would indicate that she was a young adult.

Answers to “Can You Synthesize What You’ve Learned?”

1. Passage through the birth canal can often distort the shape of an infant’s head due to the presence of fontanelles which make the cranium slightly more malleable. After birth, the same fontanelles allow the cranial bones to accommodate the quickly growing newborn brain.

2.

The physician should not prescribe the drug at this time. Thalidomide is a teratogen that interferes with fetal

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development by inhibiting the expression of numerous genes, including those involved in development of vasculature in the limbs.

3. The shape of the pelvic outlet, the proportions of the greater sciatic notch and the obturator foramen, as well as the shape of the ischial spine may be used as indicators of the sex. Age-related changes to the symphysial surface of the pubis may be used to determine the age; and the extent of osteoporosis may be an indicator of the relative health of the individual.

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Chapter 9 Answers to “What Did You Learn?”

1. There is an inverse relationship between the stability of a joint and its range of motion. The more possible movement there is at a joint, the more likely it is to sustain damage.

2. Not all fibrous joints are synarthroses. Synarthrotic joints are by definition immobile, and fibrous joints are simply held together by collagen. These two criteria are not mutually exclusive. Some fibrous joints such as sutures are synarthrotic; others, such as the interosseous membrane between the radius and ulna, are amphiarthrotic.

3. The periodontal ligaments are the only gomphoses in the body. They are located within the alveolar sockets of the mandible and maxilla, and they are synarthrotic.

4.

Sutures are synarthrotic joints between the bones of the skull. They are held together by collagen fibers.

5.

Syndesmoses are amphiarthrotic. They permit a limited range of movement.

6. Synchondroses are held together by hyaline cartilage. They may be found within the epiphyseal plates of children or the costal cartilage attaching ribs to the sternum.

7.

Symphyses are optimized for absorbing pressure and compression forces, and are primarily synarthrotic.

8. All synovial joints are diarthrotic. They consist of an articular capsule surrounding a joint cavity, which contains synovial fluid. Articular cartilage is also present at the end of each bone involved in the joint, as are numerous ligaments, nerves, and blood vessels.

9. Synovial fluid lubricates and nourishes articular cartilage at a joint. It can also act as a shock absorber distributing forces during compression.

10. Plane joints are capable of uniaxial side-to-side gliding movements. Both hinge and pivot joints are also considered uniaxial since they only move along one plane. Condyloid and saddle joints are biaxial because they permit movement in two dimensions. Lastly, ball-and-socket joints are multiaxial because they are capable of movement in three dimensions.

11. The effort arm is the length of the lever from the fulcrum to the point where force (effort) is applied. The resistance arm is the length of the lever from the fulcrum to the point where resistance is applied.

12. In a first-class lever, the fulcrum is located between the resistance and effort. In a second-class lever, the resistance is between the fulcrum and effort. In a third-class lever, effort is applied between the resistance and the fulcrum.

13.

Gliding movements occur within plane joints, such as those in between the carpals or tarsals.

14. Flexion decreases the angle at joint along an anterior-posterior plane, whereas extension increases the angle along an anterior-posterior plane. Circumduction is a sequence of movements in which the proximal end of an appendage remains relatively stationary while the distal end makes a circular motion.

15. Pronation is the medial rotation of the forearm so that the palm of the hand is directed posteriorly, crossing the radius over the ulna.

16. Inversion and eversion occur with the tarsals of the foot. The sole of the foot is turned medially during inversion, and laterally during eversion.

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17. The temporomandibular joint is both a plane joint, capable of gliding movement, and a hinge joint, capable of elevation and depression of the mandible.

18. The glenohumeral joint consists of a shallow cup with minimal support from ligaments. Most of the stability at the shoulder comes from the muscles of the rotator cuff. This provides for a wide range of motion, but sacrifices stability.

19. The anular ligament holds the head of the radius against the radial notch of the ulna. Subluxation of the elbow occurs more commonly in children because of the loose positioning of the still developing head of the radius, within a thin anular ligament.

20. The glenohumeral joint has a far greater range of motion than the hip. However, the hip is much more stable and less likely to be dislocated.

21. The anterior cruciate ligament prevents hyperextension of the knee, while also preventing the tibia from moving too far anteriorly relative to the femur. Conversely, the posterior cruciate ligament prevents hyperflexion of the knee, while also preventing posterior movement of the tibia relative to the femur.

22. The talocrural joint is formed by the articulation of the talus with both the tibia and fibula. The joint permits dorsiflexion and plantar flexion at the ankle.

23. Changes to joints begin early with the closure of epiphyseal plates, and continue well into adulthood with the ossification of the sutures in the skull. Osteoarthritis is also often incurred with age, leading to degradation of the joints.

Answers to “Do You Know the Basics?”

1. C Feedback: The glenohumeral joint is a multiaxial ball-and-socket joint. It is less stable than other ball-and-socket joints, such as the hip; however, it does have a far wider range of motion.

2. C Feedback: The sole of the foot is turned medially during inversion, and laterally during eversion.

3. B Feedback: Synostoses are completely ossified sutures.

4. C Feedback: The anterior cruciate ligament prevents hyperextension of the knee, while also preventing the tibia from moving too far anteriorly, relative to the femur.

5. D Feedback: A diarthrosis is a freely moveable joint. A saddle joint (located between the first metacarpal and carpal) is an example of a diarthrosis.

6. C Feedback: In a third-class lever such as the knee, effort is applied between the resistance and the fulcrum.

7. A Feedback: The metacarpophalangeal joints are condyloid in shape, in that they possess a shallow cup with an oval articular surface, which permits movement in two axes.

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8. D Feedback: The ligament of the head of the femur, the ligamentum teres, contains an artery running to the femur, but does not provide for stability at the hip.

9. D Feedback: Synovial fluid lubricates and nourishes structures within the synovial joint. It can also act as a shock absorber, distributing forces during compression.

10. D Feedback: The talocrural joint is formed by the articulation of the talus with both the tibia and fibula. The joint permits dorsiflexion and plantar flexion at the ankle.

11. Stability of a joint is a function of three components: the shape of articular surfaces involved, tension produced by ligaments, and muscle tone. The stability provided by these three components decreases with increased mobility at the joint.

12. While both fibrous joints and synovial joints have dense regular connective tissue holding the bones together, they differ in other anatomic features and mobility. Fibrous joints have no joint cavity and typically are either synarthroses or diarthroses. In contrast, synovial joints have a joint cavity, articular capsule lined with a synovial membrane, and articular cartilage covering the bone ends. All synovial joints are diarthroses.

13. Synarthrotic joints are immobile. The gomphosis comprising the periodontal ligament and the sutures of the skull are examples of synarthrotic joints. Synchondroses, such as costal cartilage or epiphyseal plates composed of hyaline cartilage, are also synarthrotic.

14. Both hinge and pivot joints are uniaxial diarthroses. Hinge joints such as the elbow, knee, or the interphalangeal joints consist of the junction of the convex portion of one bone, articulating with the concave portion of another bone. Within pivot joints such as the humeroradial joint or the atlantoaxial joint, a bone with a rounded surface fits into a ring formed by a ligament and another bone.

15. In a first-class lever, the fulcrum is located between the resistance and effort. In a second-class lever, the resistance is between the fulcrum and effort. In a third-class lever, effort is applied between the resistance and the fulcrum.

16. From standard anatomical position, abduction moves a feature away from the axis of the body; adduction brings the feature toward the body, back to standard anatomical position. Pronation involves the rotation of the head of the radius within the anular ligament of the elbow, resulting in the crossing of the radius over the ulna so that the palm faces to the posterior. Supination returns the pronated limb back to standard anatomical position.

17. Overeversion ankle sprains are relatively uncommon because the deltoid ligament (which supports the medial ankle and helps prevent overeversion) is so strong. The lateral ligament of the ankle (which protects against overinversion) is much weaker and prone to injury. The deltoid ligament is so strong that is rare to have an overeversion sprain; instead, the force will actually fracture the tibia and fibula and result in a Pott fracture.

18. The radial collateral ligament is responsible for stabilizing the elbow at its lateral surface, the ulnar collateral ligament stabilizes the medial side of the elbow, and the anular ligament surrounds the neck of the radius and binds the proximal head of the radius to the ulna.

19. The tibial collateral ligament stabilizes the medial surface of the knee, preventing the leg from moving laterally, relative to the femur. The fibular collateral ligament stabilizes the lateral surface of the knee, preventing the leg from moving medially, relative to the thigh. Because the tibial collateral ligament prevents excessive medial movement of the tibia, relative to the femur, it experiences the brunt of a lateral force applied to the knee.

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20. Both osteoarthritis and rheumatoid arthritis (RA) are types of arthritis, which cause damage to the joints and result in reduced function and mobility of the joint. Osteoarthritis, commonly called ‘wear and tear’ arthritis is a degenerative condition of joints caused by overuse or age, as the articular cartilage gets worn down. In contrast, RA is an autoimmune disorder where the bony mistakenly targets the synovial membrane as foreign. In the immune response, other components of the joint get damaged as well. RA occurs more frequently in females and may occur in middle aged or younger individuals.

Answers to “Can You Apply What You’ve Learned?”

1. A Feedback: The anular ligament holds the head of the radius against the radial notch of the ulna, and can be easily subluxated.

2. B Feedback: Subluxation of the elbow occurs more commonly in children because of the loose positioning of the still developing head of the radius, within a thin anular ligament.

3. C Feedback: In this case, subluxation of the elbow allowed the head of the radius to move laterally out of the anular ligament.

4. D Feedback: The lateral ligament prevents overinversion at the ankle. Likewise, overinverting the foot at the ankle can damage the lateral ligament.

5. B Feedback: The posterior cruciate ligament becomes taut on flexion, and prevents hyperflexion of the knee joint.

Answers to “Can You Synthesize What You’ve Learned?”

1. Erin has dislocated her shoulder, possibly tearing the capsule of the glenohumeral joint as the head of the humerus moved inferior, out of the glenoid cavity.

2. The knee is extremely susceptible to damage from a lateral impact. Within the knee, the tibial collateral ligament prevents excessive medial movement of the tibia, relative to the femur. Hence, it will experience the brunt of a lateral force applied to the knee. The tibial collateral ligament is directly attached to the medial meniscus of the knee, and damage to the ligament can also result in damage to the meniscus.

3. The doctor is examining Jackie’s temporomandibular joint. Wear and tear within the joint can cause inflammation, damage to the articular disc, and pain. Dislocation of the articular disc can be perceived as a clicking sound, when the jaw is opened and closed.

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Chapter 10 Answers to “What Did You Learn?”

1. The functions of skeletal muscle are: body movement, maintenance of posture, protection and support, regulating elimination of materials, and heat production.

2. (a) Contractility is exhibited when contractile proteins within skeletal muscle cells slide past one another.

Contractility is what enables muscle cells to cause body movement and to perform muscles other functions. (b) Elasticity is due to specialized protein fibers within skeletal muscle cells that act like compressed coils when a muscle contracts and shortens. When skeletal muscle contraction has ended, the tension in these proteins is released, and the muscle returns to its original length. (c) Extensibility is the lengthening of a muscle cell. For example, when you flex your elbow joint, you are contracting the biceps brachii on the anterior side of your arm, while the triceps brachii on the posterior side is extended with the motion. The reverse is true when you straighten your elbow joint.

3. Endomysium is the innermost areolar connective tissue layer. It surrounds and electrically insulates each muscle fiber. Perimysium is a dense, irregular connective tissue muscle sheath that surrounds the fascicles and contains arrays of blood vessels and nerves to supply individual muscle fibers. Epimysium is a layer of dense irregular connective tissue that surrounds the entire muscle. Deep fascia is an expansive sheet of dense irregular connective tissue external to the epimysium. It separates individual muscles; binds together muscles with similar functions; contains nerves, blood vessels, and lymph vessel; and serves to fill spaces between muscles. The superficial fascia is external to deep fascia and is composed of areolar connective tissue and adipose connective tissue that separates muscle from skin.

4. Draw and label a diagram of a sarcomere.

5. Muscle > fascicle > muscle fiber > myofibril > myofilament > sarcomere. The entire muscle is composed of bundles (fascicles) of muscle cells (called muscle fibers). Each muscle fiber (cell) contains cylindrical structures called myofibrils that compose most of its volume. Myofibrils are composed of bundles of myofilaments (contractile proteins), which are arranged in repeating microscopic cylindrical units called sarcomeres.

6. A single motor neuron and the muscle fibers it controls are called a motor unit. The number of muscle fibers in a motor unit varies. This determines the degree of control because there is an inverse relationship between the size of a motor unit and the degree of control (smaller motor units have greater control whereas larger motor units have less precise control).

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7.

8. More Na+ is outside of the cell at the sarcolemma and more K+ is inside of the cell at the sarcolemma.

9. The entry of Ca2+ into the synaptic knobs triggers the merging of synaptic vesicles with the synaptic knob plasma membrane. This results in exocytosis of acetylcholine into the synaptic cleft.

10. The two events that are linked during excitation-contraction coupling are (1) the excitation of the skeletal muscle sarcolemma at the neuromuscular junction in response to stimulation by a neurotransmitter and (2) the resulting events of contraction caused by sliding myofilaments within sarcomeres of skeletal muscle fibers.

11. Three primary events occur during excitation-contraction coupling: (1) Development of an end-plate potential at the motor end plate, which results from the binding of acetylcholine (ACh) to ACh receptors causing a rapid inflow of Na+ and a slower outflow of K+. This changes the resting membrane potential from -90 mV to –65 mV (threshold value). (2) Initiation and propagation of action potential along the sarcolemma and T-tubules, which involves the sequential opening of voltage-gated Na+ channels along the sarcolemma and T-tubules and the rapid influx of Na+.

This changes the membrane potential from -65 mV to +30 mV (depolarization). Depolarization is followed immediately by the opening of voltage-gated K+ channels along the sarcolemma and T-tubules and the rapid outflow of K+ that changes the membrane potential from + 30 mV to -90 mV (repolarization). (3) Release of calcium from the sarcoplasmic reticulum, which is triggered by the arrival of the action potential at the sarcoplasmic reticulum.

Ca2+ channels open and Ca2+ diffuses out of the sarcoplasmic reticulum into the sarcoplasm.

12. Ca2+ binds to troponin in muscle thin filaments, causing a conformational change of troponin. This affects the shape of the entire troponin-tropomyosin complex, exposing myosin binding sites.

13. Crossbridge cycling continually repeats four steps: (1) crossbridge formation (attaching myosin head to actin); (2) a power stroke (swiveling of the myosin head to pull the thin filament a small distance past the thick filament); (3) release of myosin head from actin (resulting from the binding of ATP into a site on myosin head); and (4) reset myosin head (resulting from the splitting of ATP into ADP and Pi.

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14. Binding of ATP to the myosin head causes the release of myosin from actin. The hydrolysis (splitting) of ATP then provides the energy for the conformational change and resetting of the myosin head.

15. Acetylcholinesterase degrades acetylcholine in the synaptic cleft, decreasing the excitation of the muscle fiber.

Without further stimulation, action potentials are longer propagated along the sarcolemma to stimulate the opening of calcium channels; these channels close. The Ca2+ pumps continue to move calcium ions out of the cytosol, back into the sarcoplasmic reticulum removing Ca2+ that is needed for muscle contraction (cross-bridge cycling).

16. Additional ATP is immediately generated when (1) myokinase transfers Pi from ADP to another ADP, yielding ATP and AMP, and (2) creatine kinase transfers Pi from creatine phosphate to ADP, yielding creatine and ATP. 17. The immediate energy required for muscle contraction is provided for by ATP available in the muscle fibers and the ATP formed by phosphate transfer. Glycolysis then provides a brief supply of ATP, and then aerobic respiration is able to generate even more.

18. Oxygen debt is the amount of additional oxygen that is consumed following exercise to restore pre-exercise conditions. It is necessary to replace oxygen on hemoglobin molecules in the blood and myoglobin molecules in muscle, to replenish glycogen stored in muscle fibers, to replenish ATP and creatine phosphate, and to convert lactate back to glucose.

19. Fast-twitch fibers have a faster genetic variant of myosin ATPase, faster rate of propagation along their sarcolemma, as well as faster calcium release and reuptake as compared to slow-twitch fibers. Oxidative fibers specialize in providing ATP through aerobic cellular respiration; glycolytic fibers specialize in providing ATP through glycolysis.

20. Slow oxidative (SO) fibers are slow and fatigue-resistant. Although they produce contractions that are slower and less powerful, their advantage is that they can contract over long periods of time without fatigue because ATP is supplied primarily through aerobic cellular respiration.

21. Slow oxidative (SO) fibers are predominant in many postural muscles, which are required to contract for prolonged durations.

22. The latent period corresponds to the time between the point of excitation of a muscle fiber and the point at which the contraction begins. Tension generation begins during this time but there is no change in fiber length. The contraction period begins as repetitive power strokes pull thin filaments past thick filaments. Sarcomeres shorten and muscle tension increases. The relaxation period begins with release of crossbridges and decreased calcium levels and the muscle returns to its original length.

23. Recruitment is the increase in muscle tension that occurs with an increase in stimulus intensity, resulting in an increase in the number of motor units involved, or multiple motor unit summation. This permits precise control of muscle contraction in order to exert the force needed for the action.

24. Wave summation results from the continuous stimulation of a muscle at a high enough frequency, so that relaxation is not possible in between stimuli. This results in a summation (adding together) of contractile forces, culminating in a prolonged contraction that may be necessary to assure that you do not drop something you are holding.

25. Muscle tone is the resting tension in a muscle generated by involuntary nervous stimulation of the muscle. It is required to maintain constant tension on the muscle’s tendon, which stabilizes the position of bones and joints.

26. Flexion at the elbow caused by contraction of the biceps brachii would be a concentric isotonic contraction (because the muscle is shortening as it contracts).

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27. Bending at the knees permits the muscles of the back to begin the contraction from an optimal position, with well-overlapping actin and myosin fibers, thereby generating greater force. When lifting objects by bending at the waist, muscle contraction begins with overly stretched sarcomeres, with limited overlap between actin and myosin fibers. This results in a weaker contraction.

28. Muscle fatigue may be triggered at the neuromuscular junction due to either insufficient free calcium or a low number of synaptic vesicles in the presynaptic neuron. Changes in sodium or potassium ion concentrations may affect excitation-contraction coupling by inhibiting the action potential conduction along the sarcolemma which interferes with the stimulation of Ca2+ release from the sarcoplasmic reticulum. An excess of intracellular Pi may cause muscle fatigue by interfering with the release of Pi from the myosin head from actin during crossbridge cycling. Additionally, fatigue may occur when lower amounts of Ca2+ are available for release from the sarcoplasmic reticulum. The lower Ca2+ levels results in less Ca2+ binding to troponin, producing a weaker muscle contraction.

29. When a muscle undergoes hypertrophy, each muscle fiber synthesizes more contractile proteins and more cellular structures needed for and energy production.

30. With age and decreased use, skeletal muscles begin to lose both myofilaments and muscle fibers. As myoglobin and glycogen stores decrease with age so do muscle strength and resistance to fatigue. Over time elasticity is also lost as muscle tissue is replaced by an accumulation of dense irregular connective tissue. The population of satellite cells within the muscle also decreases.

31. Cardiac muscle is: (1) composed of medium, branched individual cells, whereas skeletal muscle is composed of large, fused, multinucleated cells; (2) individual cells of cardiac muscle are joined together by intercalated discs, containing gap junctions which permit communication between individual cells, and (3) cardiac muscle is stimulated by an autorhythmic pacemaker, which is controlled by the autonomic nervous system, whereas skeletal muscle is controlled voluntarily (by the somatic nervous system).

32. Smooth muscle may be found within the walls of hollow organs (e.g., blood vessels, bronchioles, gastrointestinal tract, urinary bladder, uterus), as well as the iris and ciliary body of the eye and the arrector pili within the skin.

33. Anchoring protein structures in smooth muscle include intermediate filaments, dense bodies, and dense plaques.

The intermediate filaments link both to dense bodies (‘spot welds’) where they interact within the sarcoplasm of the smooth muscle cell and to dense plaques where they attach on the inner surface of the cell sarcolemma. Smooth muscle contractile proteins are arranged between dense bodies and dense plaques, and NOT in sarcomeres.

Therefore, neither sarcomeres nor Z discs are present in smooth muscle.

34. In smooth muscle, calmodulin is a protein that binds calcium ion to form a Ca2+-calmodulin complex. Myosin light-chain kinase is an enzyme that is activated by the Ca2+-calmodulin complex. This enzyme phosphorylates the myosin head in smooth muscle cells. The myosin head ATPase activity is inactivated when the myosin head is dephosphorylated by myosin light-chain phosphatase.

35. Smooth muscle stimulation results in the entry of calcium ions into the sarcoplasm from both interstitial fluid and sarcoplasmic reticulum. Calcium ions bind to calmodulin resulting in the formation of a Ca2+-calmodulin complex and subsequent activation of the myosin light-chain kinase (MLCK). The activated kinase (MLCK) phosphorylates the myosin head which (1) activates the myosin ATPase activity of the myosin head and (2) allows the myosin head to bind to actin to form a crossbridge. Myosin ATPase hydrolyzes ATP to produce the power stroke. The myosin head releases and reattaches to the actin repetitively which causes the actin filament to slide past the thick filaments. This sliding results in a pull on the attached dense bodies anchored to the intermediate filaments of the cytoskeleton and the dense plaques attached to the sarcolemma. The anchoring filaments move inward and the entire smooth muscle cell shortens.

36. The unique characteristics of smooth muscle that allow it to fulfill its functions are: (1) slow development of contraction (about 500 milliseconds after stimulation) due to long latent period, variations in ATPase activity, slowness of Ca2+ pumps, need to dephosphorylate myosin heads, and locking of myosin to actin [the latchbridge

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mechanism]; (2) fatigue-resistant because of [a] low energy requirements, [b] ATP supplied by aerobic cellular respiration, and [c] latchbridge mechanism provides means to maintain contraction without use of additional ATP; and (3) a broader length-tension curve than skeletal muscle that allows forceful contractions whether the smooth muscle is either compressed or stretched.

37. Smooth muscle may be stimulated by the autonomic nervous system, through the stress-relaxation response elicited by stretching of the muscle, or by endocrine hormones. It may also be stimulated by local factors within the tissue, such as decreased pH, low oxygen levels, or high levels of carbon dioxide. Smooth muscle may also be stimulated by pacemaker cells from within the tissue.

38. The stress-relaxation response occurs when smooth muscle is “stressed” by being stretched. It responds by contracting, but after a given period of time, it relaxes.

39. Multiunit smooth muscle consists of individual muscle cells innervated by neurons, and permits more precise control over muscle contractions, such as within muscles in the eye. Single-unit smooth muscle usually consists of several sheets of cells, linked together by gap junctions so that they may contract as one unit. This is a useful arrangement for the walls of hollow organs where the entire organ must contract in unison.

Answers to “Do You Know the Basics?”

1. D Feedback: A muscle fiber is an individual cell. It contains cylindrical contractile structures called myofibrils and is surrounded by a connective tissue covering called the endomysium.

2. B Feedback: An action potential is initiated and propagated along the plasma membrane of a skeletal muscle fiber that is called the sarcolemma.

3. C Feedback: In skeletal muscle fibers, Ca2+ is released from the terminal cisternae of the sarcoplasmic reticulum.

4. A Feedback: Tendons consist of dense regular connective tissue and attach muscles to bones.

5. A Feedback: The action potential travels along the sarcolemma of a muscle fiber and then is carried deep into the cell along T-tubules. As the action potential enters the cell it triggers the release of calcium ions from cisternae of the sarcoplasmic reticulum.

6. B Feedback: The I band represents the region where only actin is present; it is bisected by the Z-line, and does not overlap myosin. As sarcomeres contract, the extent of overlap between actin and myosin increases, causing the I band to shorten.

7. D Feedback: During a concentric contraction, muscle fibers contract causing the muscle and its myofibrils to shorten in length.

8. C Feedback: Troponin-tropomyosin complex undergoes a conformational change and returns to its original shape in response to the release of Ca2+and its return back into the sarcoplasmic reticulum.

9. C Feedback: During sustained, moderate exercise, fatty acids are the predominant fuel molecule for generating ATP. Sufficient oxygen must be present to use fatty acids to produce ATP.

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10. D Feedback: Both skeletal muscle and cardiac muscle contain sarcomeres; thus, both appear striated (striped) when viewed with a microscope.

11. A muscle fiber is an individual muscle cell. Myofibrils are cylindrical structures within the muscle fiber. They are composed of bundles of contractile proteins called myofilaments: thick myofilaments are bundles of myosin molecules and thin myofilaments are primarily composed of actin. Troponin and tropomyosin are regulatory proteins associated with thin filaments. The myofilaments within the myofibril are arranged in a series of repeating microscopic, cylindrical units called sarcomeres.

12.

13. A motor unit is a single motor neuron and the muscle fibers it controls. The ratio of motor neurons to muscle fibers in a motor unit corresponds to the type of movement the muscle is capable of performing. This ratio is greater in muscles that require precise control over fine movements, such as those that control the movement of the eye.

Conversely, power-generating or postural muscles in the lower limbs possess much larger motor units, with numerous muscle fibers stimulated by fewer neurons because less precise control is required.

14. c. An action potential is propagated along the sarcolemma and transverse tubules. b. Calcium ions are released from the sarcoplasmic reticulum and bind to troponin. f. Tropomyosin molecules are moved off active sites on actin. d. Myosin binds to actin, forming crossbridges. a The myosin head swivels toward the center of the sarcomere. e. Myosin heads bind ATP molecules and release from actin. g. ATPase splits ATP, providing energy to reset the myosin head.

15. The immediate means for supplying energy required for muscle contraction is provided for by the ATP available within a muscle fiber and by phosphate transfer: (1) myokinase transfers phosphate to one ADP from another ADP yielding an ATP and an AMP; (2) creatine kinase transfers a phosphate to ADP from creatine phosphate, yielding an ATP and creatine. Short-term means for supplying energy involve ATP production through glycolysis in the cytosol, and long-term means involve forming ATP through aerobic cellular respiration within mitochondria.

16. Athletes who perform quick bursts of movement require muscles with a larger proportion of fast-twitch fibers rather than slow-twitch fibers. Fast-twitch fibers initiate a contraction more quickly upon stimulation, and produce a

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stronger contraction with a shorter duration. Slow-twitch fibers would be optimum for prolonged or repetitive movements.

17. A skeletal muscle fiber stimulated when it is at a normal resting length generates a maximum contractile force because there is optimal overlap of thick and thin filaments. In contrast, weaker contractions occur in muscles that are already contracted because the thick filaments are close to the Z discs, and sliding filaments are limited in their movement. Weaker contractions also occur in muscles that are overly stretched because there is minimal thick and thin filament overlap for crossbridge formation.

18. The myosin heads of smooth muscle have modifications that allow them to form latchbridges to the actin of thin filaments. The latchbridge mechanism provides the means of maintaining muscle contraction without the use of additional ATP or becoming fatigued. Additionally, relaxation of smooth muscle requires the dephosphorylation of myosin by myosin light-chain phosphatase for relaxation of smooth muscle. In additional, smooth muscle uses primarily aerobic cellular respiration to provide ATP. 19. The stress-relaxation response occurs when smooth muscle is “stressed” by being stretched. Smooth muscle responds by contracting, but after a given period of time, it relaxes even if the stimulus is still present.

20. Multiunit smooth muscle consists of individual smooth muscle cells innervated by neurons, and permits more precise control over muscle contractions. It is present in the muscles of the iris and ciliary bodies of the eye, as well as within the arrector pili muscles of the skin. Single-unit smooth muscle typically consists of two or three sheets of cells, linked together by gap junctions between cells so that they may contract as one unit. This is a useful arrangement for the walls of hollow organs where the entire organ must contract in unison, such as the organs of the digestive, urinary, or reproductive systems.

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: Blocking the release of neurotransmitter from the presynaptic vesicle would inhibit stimulation of the muscle fiber. Since no neurotransmitter would be released, no subsequent propagation of an action potential would be elicited along the sarcolemma of the muscle fiber.

2. D Feedback: Athletes who perform quick bursts of movement require muscles with a larger proportion of fast-twitch fibers rather than slow-twitch fibers. Fast-twitch fibers initiate a contraction more quickly upon stimulation, and produce a stronger contraction with a shorter duration.

3. A Feedback: K+ and Na+ are important components in generating the action potential along the sarcolemma of the skeletal muscle fiber. Ca2+ is required to stimulate the release of neurotransmitters at the neuromuscular junction.

Calcium is also required to induce the conformational change in troponin, which allows the attachment of myosin to actin. F- is not a critical component in muscle contraction or neuron function.

4. B Feedback: The release of myosin from actin requires ATP. Upon death, when ATP is no longer available, skeletal muscles become fixed in a contracted state called rigor mortis.

5. C Feedback: At the start of exercise, muscles are initially powered by ATP from the phosphate transfer system and glycolysis. Prolonged exercise, however, requires aerobic cellular respiration. Increased cardiovascular health allows a person to exercise more vigorously for longer durations.

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Answers to “Can You Synthesize What You’ve Learned?”

1. Your anatomy and physiology class is required for a career in forensics, and one of the short essays is an explanation for why the body becomes stiff after death. Provide an answer for an individual that has an understanding of muscle physiology.

ATP is required to break the crossbridges between thick and thin filaments. However, within a few hours after the heart stops beating, ATP levels in skeletal muscle fibers have been completely exhausted. ATP is not being synthesized because cell respiration has terminated at the time of death, so no ATP is available and crossbridges cannot detach. All skeletal muscles lock into a contracted position and the body of the deceased individual becomes rigid. This physiologic state, is termed rigor mortis. It continues for about 15 to 24 hours. Rigor mortis then disappears because lysosomal enzymes are released within the muscle fibers, causing autolysis (self-destruction and breakdown) of the myofibrils. Additionally, the lack of ATP has another effect. The sarcoplasmic reticulum loses its ability to return Ca2+ from the sarcoplasm and move it back into the sarcoplasmic reticulum. As a result, the Ca2+ already present in the sarcoplasm, as well as the Ca2+ that continues to leak out of the sarcoplasmic reticulum, supports a sustained contraction in the fibers.

2. Describe the effect of the botulism toxin, which inhibits the release of acetylcholine at the neuromuscular junction. Would the poison curare, which competes for acetylcholine receptors have a similar effect? Explain.

Botulism is a potentially fatal muscular paralysis that is caused by a toxin produced by the bacterium, Clostridium botulinum. The toxin prevents the release of acetylcholine (ACh) at synaptic knobs and leads to muscular paralysis.

Curare is a potent drug that acts by preventing release of acetylcholine and the subsequent stimulation of the skeletal muscle (at the neuromuscular junction). Thus, although both botulism and curare act differently (one prevents release of acetylcholine and the other prevents the transmission of neural impulses) they have the same ultimate effect and that is flaccid muscular paralysis from lack of stimulation.

3. Smooth muscle is within the urinary bladder wall. Explain why if you initially have the sensation of having to urinate why in some cases this passes. Based your answer on the stress-relaxation response.

Smooth muscle contracts in response to being stretched. Its response, however, is not continuous if the stretch is prolonged. Instead, the smooth muscle exhibits what is called the stress-relaxation response. This occurs when smooth muscle is “stressed” by being stretched. The smooth muscle responds by contracting, but after a given period of time, it then relaxes. For example, swallowed materials entering the stomach cause its wall to stretch, and the smooth muscle in the wall initially contracts. After a period of time it relaxes, allowing additional food to more easily enter the stomach. Thus, in the current example, one may ‘feel’ the need to urinate as the bladder fills with urine because the smooth muscle in its wall is stretched, that sensation subsides and passes because the ‘stretched’ smooth muscle will relax.

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Chapter 11 Answers to “What Did You Learn?”

1. The less moveable attachment of a muscle is called its origin. The more moveable attachment of the muscle is its insertion. Usually, the insertion is pulled toward the origin.

2.

Parallel muscles have a lot of endurance but are relatively weaker than pennate muscles.

3. The agonist is the prime mover for an action and generates the majority of the force. The synergist facilitates the movement produced by the agonist by either contributing tension or stabilizing the bones involved.

4. A description of the shape of a muscle may be incorporated into its name: A deltoid muscle is triangular in shape, orbicularis implies that the muscle has fibers arranged in a circle, a rhomboid muscle has the shape of a rhomboid, and the trapezius muscle is shaped like a trapezoid. The length of the muscle may also be incorporated into the nomenclature: The terms longus and longissimus refer to relatively long muscles and brevis refers to short muscles.

5. The gluteus maximus gets its name from (1) the gluteal region of the body (buttocks) = gluteus, and (2) the size of the muscle = maximus (largest).

6.

The levator anguli oris, zygomaticus major, zygomaticus minor, and risorius muscles all contribute to smiling.

7.

The depressor anguli oris contracts to pull the corners of the mouth inferiorly when frowning.

8.

The lateral rectus muscle abducts the eye.

9. The pterygoid muscles are responsible for protraction and side-to-side movement of the mandible. The medial pterygoid muscle may also elevate the mandible.

10. The extrinsic tongue muscles are used in various combinations to accomplish the precise, complex, and delicate tongue movements required for proper speech and manipulating food within the mouth.

11. The digastric, geniohyoid, mylohyoid, and stylohyoid muscles are suprahyoid muscles. All four are capable of elevating the hyoid bone.

12. The sternocleidomastoid and scalene muscles flex the neck. Extension at the neck may be accomplished by the splenius capitis, splenius cervicis, longissimus capitis, rectus capitis posterior major, or rectus capitis posterior minor muscles.

13. The erector spinae is the largest muscle mass in the back. The muscles of the erector spinae consist of three groups of muscles: iliocostalis (located laterally), longissimus (located intermedially), and spinalis (located medially). The muscles of the erector spinae are used to maintain posture and help us stand erect.

14. The external intercostal muscles elevate the ribs during inspiration. The internal intercostals depress the ribs, but only during a forced expiration; a normal exhalation takes no active muscular effort.

15. Contraction of the diaphragm moves the entire muscle inferiorly, which expands the thoracic cavity, thus decreasing pressure in the thoracic cavity and increasing pressure in abdominopelvic cavity.

16. All four abdominal muscles compress the abdominal wall. The rectus abdominis flexes the vertebral column.

The external and internal obliques and the transverse abdominis muscles produce lateral flexion when contracted unilaterally, or contribute to flexion of the vertebral column when both sides contract simultaneously. The oblique muscles are also capable of rotating the vertebral column.

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17. The pelvic floor muscles form the pelvic diaphragm across the pelvic outlet, and support the viscera of the pelvic cavity.

18. The levator scapulae elevates and rotates the scapula inferiorly. The rhomboid major and minor elevate, adduct, and rotate the scapula inferiorly. The trapezius may elevate, depress, retract, or rotate the scapula superiorly.

19.

In general, all posterior thoracic muscles either adduct or extend the arm at the shoulder.

20. The subscapularis rotates the arm medially, the supraspinatus abducts the arm, the infraspinatus adducts and rotates the arm laterally, and the teres minor muscle adducts and rotates the arm laterally.

21. The anterior compartment of the arm contains the three flexors of the elbow: the biceps brachii, brachialis, and brachioradialis muscles. Along with flexion at the elbow, the biceps brachii participates in flexion at the shoulder and supination of the elbow. The two pronators, pronator teres and pronator quadratus, are also located within the anterior compartment.

22. The pronator teres and pronator quadratus pronate the arm. Their antagonists, the biceps brachii and supinator muscles, supinate the arm.

23.

Muscles in the anterior compartment of the forearm are all flexors of the wrist.

24. The abductor pollicis longus abducts the thumb, whereas the extensor pollicis longus and brevis extend the metacarpophalangeal joint of the thumb.

25. The abductor pollicis brevis abducts the thumb. The dorsal interossei muscle abducts fingers 2–5 because the abductor digiti minimi muscle abducts finger 5.

26. Thigh flexors are located within the anterior compartment of the thigh, adductors are located within the medial compartment, and abductors are located within the lateral compartment. There is also a posteriorly located gluteal group and hamstring group responsible for extension.

27. The biceps femoris, semitendinosus, and semimembranosus, collectively called the hamstring group, are the primary flexors of the leg. The sartorius, gracilis, and gastrocnemius muscles also facilitate in flexion of the leg.

28. The anterior compartment of the leg contains dorsiflexors of the foot and extensors of the toes. The lateral compartment contains evertors and plantar flexors of the foot. The posterior compartment of the leg contains plantar flexors and flexors of the leg and toes.

29. The extensor hallucis longus muscle extends the metacarpophalangeal joint of the great toe. The extensor digitorum brevis muscle extends both the metacarpophalangeal and proximal interphalangeal joints of toes 2–5.

The deeper lumbrical muscle extends the proximal and distal interphalangeal joints of toes 2–5.

Answers to “Do You Know the Basics?”

1. B Feedback: The agonist is the prime mover at a joint. A synergist muscle may contribute force to the movement or help stabilize the joint during the movement, but it is the agonist that generates the majority of the force.

2. A Feedback: Contraction of the sternocleidomastoid muscles in unison flexes the cervical vertebrae, which is flexion of the head at the neck.

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3. C Feedback: The diaphragm depresses as it contracts, simultaneously increasing the volume of the thoracic cavity and decreasing the volume of the abdominal cavity.

4. B Feedback: The inferior oblique muscle both depresses and adducts the eye.

5. C Feedback: The spinalis group of muscles participates in flexion of the vertebral column.

6. B Feedback: The dorsal interossei muscles of the hand are capable of flexion of metacarpophalangeal joints 2–5, extension of the proximal and distal interphalangeal joints of fingers 2–5, or abducting fingers 2–5.

7. B Feedback: All of the muscles within the anterior compartment of the leg are capable of dorsiflexion of the foot.

The extensor digitorum longus and extensor hallucis longus also extend the toes.

8. D Feedback: The brachialis, biceps brachii, and brachioradialis muscles all flex the arm at the elbow. The anconeus muscle is located within the posterior compartment of the arm and participates in extension.

9. C Feedback: The muscles of the hamstring group – the semitendinosus, semimembranosus, and biceps femoris – all originate at the ischial tuberosity and can extend the thigh at the hip or flex the leg at the knee.

10. B Feedback: The gastrocnemius, located within the posterior compartment of the leg, is a primary mover for plantar flexion of the foot.

11. Muscles can be named according to (1) orientation of muscle fibers, (2) muscle attachments, (3) specific body regions, (4) muscle shape, (5) muscle size, (6) muscle heads/tendons of origin, (7) muscle function/movement, and (8) muscle position at body surface.

12. Smiling requires contraction of the levator anguli oris, zygomaticus major, and zygomaticus minor to elevate the corners of the mouth. The risorius also contracts when you make a closed-mouth smile. Closing of the eyes is accomplished by the orbicularis oculi muscle. Closing or pursing of the lips is performed by the orbicularis oris, whereas closing the mouth is accomplished by the masseter and temporalis muscles, which elevate the mandible.

13. The suprahyoid muscles are located superior to the hyoid bone, and the infrahyoid muscles are located inferior to the hyoid bone. The suprahyoid muscles are associated with the floor of the mouth. In general, these muscles elevate the hyoid bone during swallowing and speaking. Contraction of the infrahyoid muscles will either depress the hyoid bone or depress the thyroid cartilage of the larynx.

14. The external and internal oblique muscles laterally flex the vertebral column (bend the body laterally) and rotate the vertebral column to the opposite side if they contract unilaterally. If these muscles bilaterally contract, they compress the abdominal wall and flex the vertebral column.

15. Movements possible at the glenohumeral joint are (1) abduction by the deltoid muscle, (2) adduction by the latissimus dorsi and pectoralis major, (3) extension by the latissismus dorsi and deltoid, (4) flexion by the pectoralis major and deltoid, (5) lateral rotation by the infraspinatus and teres minor, and (6) medial rotation by the subscapularis.

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16. The anterior compartment of the brachium primarily contains elbow flexors: the biceps brachii, brachialis, and brachioradialis. The posterior compartment contains extensors of the elbow: the triceps brachii and the anconeus. Because the biceps and triceps brachii also have attachments on the scapula, they also participate in extension and flexion, respectively, of the glenohumeral joint.

17. The flexor digitorum profundus lies deep to the flexor digitorum superficialis. Both muscles insert by way of four separate tendons into phalanges 2–5. The tendons of flexor digitorum profundus insert at the distal phalanges of digits 2–5, whereas the tendons of flexor digitorum superficialis only insert at the middle phalanges. Therefore, although both muscles are capable of flexing the wrist, the metacarpophalangeal joints, and the proximal interphalangeal joints, only the flexor digitorum profundus is capable of flexing the distal interphalangeal joints of digits 2–5.

18. The gluteus maximus is the primary mover for extension at the hip. The adductor magnus, biceps femoris, semitendinosus, and semimembranosus muscles act as synergists.

19. Balancing on the toes involves plantar flexion of the foot, which is accomplished primarily by the gastrocnemius and soleus muscles.

20.

Inversion of the foot is accomplished by the tibialis anterior and tibialis posterior muscles.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: The orbicularis oculi muscle is responsible for closing of the eye, such as blinking or squinting.

2. C Feedback: The medial rectus muscle adducts the eye.

3. D Feedback: The extensors of the forearm are located in the posterior compartment of the brachium. The flexors are located in the anterior compartment.

4. A Feedback: The four heads of the quadriceps femoris muscle are located within the anterior compartment of the thigh. They are the primary movers for extension at the knee.

5. C Feedback: The fibularis tertius, longus, and brevis muscles originate at the fibula. All three are involved in eversion of the foot.

Answers to “Can You Synthesize What You’ve Learned?”

1. The inguinal region is one of the weakest areas of the abdominal wall. Within this region is the inguinal canal that allows the passage of the spermatic cord into the testis. This is the most common site of a rupture or separation of the abdominal wall in males. It is possible for rising pressure in the abdominal cavity, as might develop while straining to lift a heavy object, to push a segment of the small intestine into the canal causing a hernia. Since exercise can increase abdominal muscle tone, it can also help prevent an inguinal hernia.

2. The external urethral sphincter is located amongst the muscles of the pelvic floor. These muscles may have been damaged upon impact, which may have caused her to have difficulty controlling the release of urine from the bladder.

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3. Exercises that involve flexion of the elbow, such as biceps curls, would help to strengthen the biceps brachii, brachialis, and brachioradialis muscles. Extension exercises such as bench dips or close-grip bench presses would help to strengthen the triceps brachii as well as the anconeus muscles. Pronation/supination exercise such as pronating and supinating the arm while holding a weight, with the elbow held at a 90-degree angle, would help strengthen the pronator teres and pronator quadratus, as well as the supinator muscles.

4. Flexion of the elbow when the arm is prone decreases the contribution of the brachioradialis muscle to the force of contraction, thereby relying primarily on the brachialis and biceps brachii.

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Chapter 12 Answers to “What Did You Learn?”

1. Receptors monitor changes in both the internal and external environment called stimuli. Effectors include all three types of muscle tissue (skeletal muscle, cardiac muscle, and smooth muscle) and glands.

2. The nervous system is functionally separated into the sensory nervous system and motor nervous system. The sensory nervous system is responsible for receiving and processing sensory information from receptors. The motor nervous system is responsible for initiating and transmitting motor output to effectors (muscles or glands).

3. Excitability is the ability of a cell to respond to a stimulus that causes a local change in the membrane potential (called a graded potential). Conductivity refers to a neuron's ability to propagate an electrical change along its plasma membrane (called an action potential). Secretion describes the neuron's ability to release neurotransmitters in response to an action potential.

4. Dendrites are relatively short, small, unmyelinated processes that branch off the cell body, which conduct graded potentials toward the cell body. An axon (nerve fiber) is a relatively longer projection that propagates action potentials away from the cell body. Synaptic vesicles contain neurotransmitters within synaptic knobs. Neurofibrils are aggregated bundles of cytoskeleton intermediate filaments within the neuron that provide structural support.

5. Anterograde transport is the movement of materials from the cell body to synaptic knobs, and retrograde transport is the movement of materials from synaptic knobs to the cell body. Fast axonal transport is both anterograde and retrograde; it can move in either direction. Vesicles, organelles, and glycoproteins required at the distal end of the neuron are moved by anterograde transport, whereas used vesicles and potentially harmful products are moved by retrograde mechanisms back to the cell body.

6. The four structural types of neurons are classified based on the number of processes emanating directly from the cell body: Multipolar neurons have one axon and multiple dendrites, whereas bipolar neurons have one axon and only one dendrite. A unipolar neuron has a single, short neuron process that branches into two distinct ends.

Anaxonic neurons possess only dendrites and no axon.

7. Interneurons are located entirely within the central nervous system. They receive stimulation from other neurons and carry out the integrative function of the nervous system. In other words, they are responsible for receiving, processing, and storing information within the CNS. 8. Individual axons in the PNS are surrounded by neurolemmocytes and then wrapped in a delicate layer of areolar (loose) connective tissue called the endoneurium. Groups of axons are wrapped into bundles, called nerve fascicles, by a dense irregular connective tissue layer called the perineurium. All of the fascicles are bundled together in a nerve that is enclosed by dense irregular connective tissue layer called the epineurium.

9. A synapse is the specific location where a neuron is functionally connected either to another neuron or an effector.

Most synapses within the nervous system are chemical synapses. A chemical synapse between two neurons is composed of a presynaptic neuron, which is the signal producer, and the postsynaptic neuron, which is the signal receiver or target. They are separated by a fluid-filled gap called the synaptic cleft. Transmission at a chemical synapse occurs when neurotransmitter molecules stored in synaptic vesicles are released from the synaptic knob of the presynaptic neuron into the synaptic cleft. Some of the neurotransmitter diffuses across the cleft to bind to receptors within the postsynaptic neuron plasma membrane to initiate another electrical signal.

10. Glial cells retain the ability to replicate (mitotic ability). This leaves them far more susceptible to possibly unrestricted growth. Therefore, they are more likely to be the source of a brain tumor than neurons.

11. Microglial cells replicate in response to an infection within the brain.

12. Neurolemmocytes form myelin sheaths around axons in the peripheral nervous system.

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13. Myelin sheaths electrically insulate axons in both the peripheral nervous system and central nervous system, which serve to increase the velocity of action potential propagation along the axolemma (the axon’s plasma membrane). Myelination in the peripheral nervous system begins with a neurolemmocyte wrapping around a portion of the axon of a neuron. The wrapping continues until there are multiple layers of myelin around the axon.

Collectively, the overlapping layers of neurolemmocyte plasma membrane form the myelin sheath. The cytoplasm and nucleus of the neurolemmocyte is pushed to the periphery forming the neurilemma.

14. The success of PNS axon regeneration depends upon two primary factors: (1) the amount of damage, and (2) the distance between the site of the damaged axon and the structure it innervates.

15. After an axon is severed, the distal end of the axon and the myelin sheath degenerates through a process called Wallerian degeneration. Macrophages remove the debris. However, the neurilemma in this region may survive. The proximal portion of the severed end seals and begins to swell. The neurilemma together with the remaining endoneurium forms a regeneration tube. The axon regenerates and re-myelination occurs. The regeneration tube guides the axon sprout as it grows under the influence of nerve growth factor released by the neurolemmocytes.

Innervation is restored as the growing axon contacts the original receptor or effector.

16. There are three states of voltage-gated channels: resting, activation and inactivation. (1) In the resting state, the inactivation gate is open but the inactivation gate is closed: Na+ entry is prevented. (2) In the activation state, both the inactivation gate and the activation gate are open: Na+ enters the cell through the open channel. (3) In the inactivation state, the activation gate is open but the inactivation gate is temporarily closed following activation of the Na+ channel: Na+ entry is prevented. Note: the resting state of voltage-gated Na+ channels is reestablished as the inactivation gate opens and activation gate closes.

17. Chemically gated channels are located in the receptive segment. In contrast, voltage-gated channels are present in the initial, conductive, and transmissive segments.

18. Current is the movement of charged particles (ions) across a barrier (the phospholipid bilayer). Voltage is a measure of the amount of difference in charge across the phospholipid bilayer. Resistance is the opposition to the movement of charged particles. Within a neuron, the phospholipid bilayer of the plasma membrane provides the resistance. The charge difference on either side of the plasma membrane is the voltage (at rest this is the resting membrane potential). Opening or closing of channels within the plasma membrane change resistance and permit a current, which is the flow of ions through the membrane.

19. The resting membrane potential in a neuron is the electrical charge difference across the membrane when the neuron is at rest. It is typically -70 millivolts, but it can range between -40 and -90 millivolts. There is relatively more K+ within the cytosol than in the interstitial fluid around the neuron. In contrast there is more Na+ and Cl- in the interstitial fluid than within the cytosol. At the synaptic knob, there is more Ca2+ in the interstitial fluid than within the cytosol. All gated channels (voltage gated Na+. K+ and Ca2+) are closed.

20. An RMP is primarily a consequence of ion movement across the plasma membrane through leak channels. K+ diffusion is the most important factor. It is dependent upon its electrochemical gradient. K+ moves out of the neuron down its chemical concentration gradient, however this movement is opposed by the electrical gradient (both the positive charge on the outside of the cell and the negative charge on the inside of the cell). When the K+ chemical gradient equals the electrical gradient that opposes this movement, K+ movement has reached equilibrium.

Na+ enters the cell through leak channels moving down both its chemical concentration gradient and electrical gradient. There are fewer Na+ leak channels so there is less movement of Na+. Na+/K+ pumps then play a small role in establishing and maintaining a resting membrane potential, but instead play an important function in maintaining the concentration gradients for both K+ and Na+.

21. An excitatory postsynaptic potential (when the inside of the cell becomes relatively more positive than the RMP) is generated when binding of neurotransmitter from the presynaptic neuron to chemically-gated cation channels in the receptive segment of the postsynaptic neuron allows more Na+ to enter the cell (than K+ exits the cell). An inhibitory postsynaptic potential (when the inside of the cell becomes relatively more negative than the RMP) is generated when binding of neurotransmitter from the presynaptic neuron to chemically-gated channels in the receptive segment of the postsynaptic neuron allows either more K+ to leave the cell or more Cl- to enter the cell.

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22. The threshold membrane potential is the voltage that must be reached in order to generate an action potential within the initial segment of a neuron. Typically this is at −55 mV, which is about +15 mV above the resting membrane potential. This voltage change is large enough to trigger the opening of voltage-gated channels in the initial segment.

23. Depolarization occurs when the threshold membrane potential voltage of −55 mV is reached; then voltage-gated Na+ channels open and Na+ rapidly enters the cell, reversing the polarity of the plasma membrane from negative to positive. Repolarization occurs due to closure of the voltage-gated Na+ channels and opening of voltage-gated K+ channels. K+ moves out of the cell and membrane polarity is reversed from positive to negative.

24. An action potential involves a temporary reversal of polarity across the plasma membrane and involves two processes: (1) Depolarization is the reversal of polarity at the plasma membrane inside the cell from negative to positive and (2) Repolarization is the return to polarity at the plasma membrane inside the cell from positive to negative. Continuous propagation occurs in unmyelinated axons. It involves sequential opening of voltage-gated Na+ channels and voltage-gated K+ channels along the entire length of the axon plasma membrane. Saltatory Conduction occurs in myelinated axons. Action potentials only occur at neurofibril nodes. Myelinated regions of an axon are insulated by myelin which prevents ion movement across the membrane. Thus, the transmission of a nerve signal seems to ‘jump’ from node to node.

25. The arrival of the action potential at the synaptic knob triggers the opening of voltage-gated Ca2+ channels.

Calcium enters the knob from the interstitial fluid and bind to proteins associated with the synaptic vesicles. This causes the fusion of the synaptic vesicles with the neuron plasma membrane and neurotransmitter is released from the synaptic vesicle into the synaptic cleft by exocytosis.

26. A graded potential occurs within the receptive segment of a neuron through the opening of chemically gated channels. The direction of the change can be positive (an excitatory postsynaptic potential) or negative (an inhibitory postsynaptic potential). The amount of voltage change associated with a graded potential is relatively small, with the specific amount of voltage change being dependent upon the amount of stimulation. (Larger amounts of stimulation produce larger graded potentials.) The small ion currents of a graded potential experience resistance so they become weaker and travel only small distances. In comparison, an action potential is generated within the initial segment and is propagated at the same intensity along an axon of the neuron through the sequential opening of voltage-gated channels. It involves sufficient movement of ions to change the membrane potential from negative to positive (depolarization) and then from positive to negative (repolarization).

27. Group A fibers have conduction velocities that may be as fast as 150 meters per second; these fibers have both a large diameter and are myelinated. Most somatic sensory neurons that extend from receptors to the CNS, and all somatic motor neurons that extend from the CNS to skeletal muscles, are included in this group.

28. Action potential frequency is the number of action potentials that are propagated along an axon per time. Action potential frequency can vary. As the stimulus strength increases, the frequency of action potentials increases (up to the point of maximum frequency). Action potential velocity is the speed (or rate) that the action potential is propagated. Action potential velocity can also vary and is influenced primarily by two factors: axon diameter and myelination of the axon. Velocity is generally faster in axons with a larger diameter. The myelination of the axon is the more important factor. Propagation of an actin potential occurs more rapidly in myelinated axons than in unmyelinated axons.

29. Neurotransmitters are classified based upon their chemical structure and function. There are four chemical structure categories: (1) acetylcholine, (2) biogenic amines [monoamines], (3) amino acids, and (4) neuropeptides [or peptides]. There are four functional categories: two are based upon effect of the neurotransmitter on membrane potential of a target cell (1) excitatory and (2) inhibitory, and two are based upon target cell response (3) direct causes opening of an ion channel and (4) indirect - activates a second messenger pathway involving G proteins that results in a more diverse effects.

30. The affect that acetylcholine has on target cells depends on the specific receptor type in the plasma membrane of the target cell. One type of receptor may cause the production of and EPSP (an excitatory effect) whereas a different receptor may cause and IPSP (an inhibitory effect).

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31. Nitric oxide is a molecule (not a classical neurotransmitter) that locally regulates or alters the response of neurons to neurotransmitters. Thus it becomes a participant in the “decision making” occurring during transmission of information by the nervous system. It may either facilitate or inhibit a response.

32. In a converging circuit, a single postsynaptic neuron receives input from several presynaptic neurons.

33. A reverberating circuit utilizes feedback to produce a repeated, cyclical stimulation of the same circuit. Once activated, it may continue to function until the cycle is broken by either inhibitory stimuli or synaptic fatigue. In a parallel after-discharge circuit, input is transmitted simultaneously along several neuron pathways to a common postsynaptic cell. The number of neurons (and number of synapses) in each pathway vary as does the amount of time to transmit the information. This reinforces the repetitive neural activity needed for higher order thinking.

Answers to “Do You Know the Basics?”

1. A Feedback: Neurotransmitters are released from the synaptic knobs, distal to both the cell body and the axon.

2. B Feedback: Bipolar neurons have two processes extending from the cell body; one axon and one dendrite.

3. D Feedback: Interneurons are located only within the central nervous system where they receive, process, and store information in order to carry out the integrative function of the nervous system.

4. B Feedback: As Na+ moves down its concentration gradient and enters a neuron, it causes a slight depolarization (slightly more positive membrane potential), which is the excitatory postsynaptic potential (EPSP).

5. C Feedback: Mature ependymal cells are located within the lining of CNS ventricles. They are ciliated and participate in the production and circulation of cerebrospinal fluid.

6. D Feedback: Neurolemmocytes are glial cells that are responsible for myelination of neurons in the peripheral nervous system.

7. B Feedback: Voltage-gated Na+ channels open at −55 mV, which is the threshold value.

8. C Feedback: Reverberating circuits utilize feedback to produce a repeated, cyclical stimulation of the circuit.

9. B Feedback: An electrical synapse is composed of a presynaptic neuron and a postsynaptic neuron physically bound together. Gap junctions are present in the plasma membranes of both neurons and facilitate the flow of ions between the cells.

10. A Feedback: Myelination significantly increases the velocity of conduction along a neuron because an action potential is only generated at neurofibril nodes, thus it appears to ‘jump’ from node to node.

11. Neurons are classified structurally by the number of neuron processes emanating directly from the cell body: Multipolar neurons have one axon and many dendrites, bipolar neurons have one axon and only one dendrite, and a unipolar neuron consists of a single short neuron process that emerges from the cell body and branches like a T.

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Anaxonic neurons have only dendrites and no axon. Neurons are classified functionally according to the direction the action potential travels relative to the CNS: sensory, motor, and association. Sensory neurons (afferent) conduct sensory input toward the CNS. Motor neurons (efferent) conduct motor output away from the CNS. Interneurons (association) lie entirely within the CNS. 12. The glial cells within the central nervous system are astrocytes, ependymal cells, microglia and oligodendrocytes, whereas those within the peripheral nervous system are satellite cells and neurolemmocytes. In the CNS, astrocytes carry out numerous important functions including: formation of the blood-brain barrier, regulation of interstitial fluid composition, structural network, assisting neuronal development, and occupy the space of dying neurons. Ependymal cells are ciliated and line brain ventricles and the spinal cord central canal. Together with neighboring capillaries they form the choroid plexus and help produce the cerebrospinal fluid (their cilia help to circulate it). Microglial cells are small and have slender branches. They are phagocytic cells that function to eliminate microbes (infectious agents) and remove cellular debris. Oligodendrocytes are large cells with a bulbous body and slender cytoplasmic processes that help provide myelin wrapping around axons in the CNS. Within the peripheral nervous system, satellite cells are flattened and arranged around neuronal cell bodies within ganglia.

They separate cell bodies in a ganglion from their surrounding interstitial fluid and help electrically insulate these cells and regulate nutrient exchange and waste product removal. Neurolemmocytes are flattened cells that form the myelin sheath around axons in the PNS. 13. Myelination is the process by which part of an axon is wrapped with myelin (the insulating covering around the axon consisting of numerous concentric layers of glial cell plasma membranes. A neurilemma is formed. In the CNS, an oligodendrocyte can myelinate many axons at the same time because of its numerous processes, and no neurilemma is formed. In the PNS, a neurolemmocyte can myelinate only a single, small portion of one axon in the PNS, and a neurilemma is formed.

14. A PNS axon may repair itself through the process of axon regeneration (called Wallerian degeneration). After an axon in the PNS is severed, the proximal portion of the severed end seals and begins to swell. The distal severed region degenerates and is phagocytized. The neurolemmocytes in the distal region survive and together with the remaining endoneurium form a regeneration tube. The axon regenerates and re-myelination occurs. The regeneration tube guides the axon sprout as it grows under the influence of nerve growth factor released by the neurolemmocytes.

Innervation is restored as the growing axon contacts the original receptor or effector.

15. An RMP is primarily a consequence of ion movement across the plasma membrane through leak channels. K+ diffusion is the most important factor. It is dependent upon its electrochemical gradient. K+ moves out of the neuron down its chemical concentration gradient, however this movement is opposed by the electrical gradient (both the positive charge on the outside of the cell and the negative charge on the inside of the cell). When the K+ chemical gradient equals the electrical gradient that opposes this movement, K+ movement has reached equilibrium.

Na+ enters the cell through leak channels moving down both its chemical concentration gradient and electrical gradient. There are fewer Na+ leak channels so there is less movement of Na+. Na+/K+ pumps then play a small role in establishing and maintaining a resting membrane potential, but instead play an important function in maintaining the concentration gradients for both K+ and Na+.

16. An action potential is generated within the initial segment and is propagated at the same intensity along an axon of the neuron through the sequential opening of voltage-gated channels. It involves sufficient movement of ions to change the membrane potential from negative to positive (depolarization) and then from positive to negative (repolarization). In comparison, a graded potential occurs within the receptive segment of a neuron through the opening of chemically gated channels. The direction of the change can be positive (an excitatory postsynaptic potential) or negative (an inhibitory postsynaptic potential). The amount of voltage change associated with a graded potential is relatively small, with the specific amount of voltage change being dependent upon the amount of stimulation. (Larger amounts of stimulation produce larger graded potentials.) The small ion currents of a graded potential experience resistance so they become weaker and travel only small distances.

17. The entry of positively charged Na+ into the receptive segment of a neuron causes the inside to become relatively more positive (a condition called an excitatory postsynaptic potential [EPSP]. Either the exit of positively charged K+ or the entry of negatively charged Cl- into the receptive segment of a neuron causes the inside to become relatively more negative (a condition called an inhibitory postsynaptic potential [IPSP]. The currents of ions (that

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associated with both EPSPs and IPSPs) move along the plasma membrane toward the initial segment. These postsynaptic potentials are “added together” in the initial segment by a process called summation. The sensitivity of voltage-gated channels to open in response to a minimum voltage change in membrane potential is the determining factor if an action potential is initiated. The minimum voltage change is called the threshold membrane potential. If a threshold membrane potential is reached, the opening of voltage-gated channels is initiated and an action potential is generated that will travel along the axon.

(-70 mV  -55 mV)

18.

(-80 mV  -70 mV)

(-70 mV  - 80 mV)

19. Depolarization resulting as the arrival of the action potential at the synaptic knob triggers the opening of voltagegated Ca2+ channels. Calcium enters the synaptic knob and binds to proteins associated with synaptic vesicles.

These vesicles then fuse with the plasma membrane for the exocytosis of neurotransmitter into the synaptic cleft.

20. Neurotransmitters are classified based upon their chemical structure and function. There are four chemical structure categories: (1) acetylcholine, (2) biogenic amines [monoamines], (3) amino acids, and (4) neuropeptides [or peptides]. There are four functional categories: two are based upon effect of the neurotransmitter on membrane potential of a target cell (1) excitatory and (2) inhibitory, and two are based upon target cell response (3) direct causes opening of an ion channel and (4) indirect—activates a second messenger pathway involving G proteins that results in a more diverse effects.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: Fast axonal transport is used to move materials from the synaptic knob to the cell body.

2. C Feedback: Astrocytoma is a tumor that forms from astrocytes in the brain.

3. C Feedback: Calcium ions enter the synaptic knob and binds synaptic vesicles containing neurotransmitter triggering events that result in the fusion with the neuron plasma membrane resulting in the release of neurotransmitter into the synaptic cleft.

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4. C Feedback: The transmissive segment (synaptic knob) releases neurotransmitter into the synaptic cleft. Some neurotransmitters such as serotonin are normally removed from the synaptic cleft by reuptake (i.e., the neurotransmitter molecules are returned to the synaptic knob).

5. A Feedback: A reverberating circuit is associated with repetitive processing.

Answers to “Can You Synthesize What You’ve Learned?”

1. As the immune system destroys neurolemmocytes in the peripheral nervous system, saltatory conduction is prevented, and conduction of action potential in the neurons of CNS is greatly diminished, possibly affecting vision and motor control.

2. Repair of damaged neurons is possible only if the amount of damage or the distance of the damage to the target is minimal. Regeneration requires formation of a regeneration tube from the remnants of the neurilemma and endoneurium of the original neuron. Growth of the new axon within the tube then occurs at approximately 2–5 mm per day—a rate much slower than blood vessel repair.

3. Depolarization of the axon requires the opening of voltage-gated Na+ channels. Neurotoxins that affect the opening of these channels would inhibit depolarization, and subsequently the action potential, along the axon.

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Chapter 13 Answers to “What Did You Learn?”

1. The brain is composed of four major regions: the cerebrum, diencephalon, brainstem, and cerebellum.

2. A neural groove is formed as the cells on the periphery of the neural plate divide and produce neural crests. As the crests continue to expand, they merge, surrounding the neural groove, which now becomes the neural tube.

3. The five secondary brain vesicles are the telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon. In the adult brain, the telencephalon forms the cerebrum; the diencephalon forms the thalamus, hypothalamus, subthalamus, and epithalamus; the mesencephalon forms the rostral end of the brainstem; the metencephalon forms the pons and cerebellum; and the myelencephalon forms the medulla oblongata.

4. Gray matter of the cerebrum is located within the outer cerebral cortex, as well as within deeper cerebral nuclei. Within the spinal cord, gray matter is limited to one large central portion, surrounded by columns of white matter.

5. Pia mater, subarachnoid space, arachnoid mater, subdural space, inner meningeal layer of dura mater, and outer periosteal layer of dura mater. Dural venous sinuses are located between the inner meningeal and outer periosteal layers of dura mater.

6. The falx cerebri is a large fold of dura mater located along the midsagittal plane within the longitudinal fissure, separating the left and right hemispheres of the brain. It is attached anteriorly to the crista galli and posteriorly to the internal occipital crest, stabilizing the brain within the cranium.

7. The fourth ventricle is located between the pons and cerebellum. It opens to the subarachnoid space via a single median aperture and paired lateral apertures.

8. The CSF provides the brain with buoyancy. Allowing the brain to float within a surrounding fluid distributes its weight within the cranium, protecting it from damage. CSF also provides a liquid cushion to protect delicate neural structures from sudden movements. Lastly, the CSF provides for environmental stability; it transports nutrients and chemical messengers to the brain, and removes waste products.

9. CSF is produced by the choroid plexus within the ventricles. It flows from the lateral ventricles and third ventricle into the cerebral aqueduct and then into the fourth ventricle. Additionally, a relatively small amount of CSF from the central canal of the spinal cord travels to the fourth ventricle as well. Most of the CSF in the fourth ventricle flows into the subarachnoid space by passing through openings in its membranous roof, either the paired lateral apertures or the single median aperture. CSF flows through the subarachnoid space surrounding the brain, spinal cord, and nerve fibers. As additional CSF is incorporated into the subarachnoid space, one-way flaps in the arachnoid villi open into the dural venous sinuses, allowing excess CSF to be released into the venous bloodstream.

These flaps allow the CSF to be released into the blood without allowing any venous blood to enter the subarachnoid space.

10. The blood-brain barrier strictly regulates which substances can and cannot enter the interstitial fluid of the brain from capillaries.

11. In most people, the left hemisphere is called the categorical hemisphere. It is specialized for language, and performing sequential or analytical reasoning. The opposite hemisphere then takes on the role of representational functions such as visuospatial relationships and analyses.

12.

The corpus callosum provides the main method of communication between the hemispheres of the brain.

13. The five lobes are the frontal lobe, parietal lobe, temporal lobe, occipital lobe, and insula. The frontal lobe is primarily concerned with voluntary motor functions, concentration, verbal communication, decision making, planning, and personality. The parietal lobe is concerned with sensory reception as well as understanding speech

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and formulating words. The temporal lobe is involved with hearing, interpreting speech and language, and smell.

The occipital lobe receives and processes incoming visual information and compares it to past visual experiences.

The insula is involved in memory and the interpretation of taste.

14. The primary motor cortex is responsible for the control of voluntary skeletal muscle activity, and is located within the precentral gyrus of the frontal lobe. The motor speech area regulates patterns of breathing and controls the muscular movements necessary for vocalization. It is located within the lateral portion of the left frontal lobe.

The frontal eye field is on the superior surface of the middle frontal gyrus, and regulates eye movements necessary for binocular vision.

15.The general function of association areas is to receive input from the primary cortical region and integrate the current sensory or motor information with previous experiences.

16. A teenager’s prefrontal cortex is not fully myelinated, and this cortex has not yet ‘pruned’ all of the unnecessary synapses. Thus, compared to an adult, a teenager is more likely to be impulsive, more emotional, and less likely to weigh the consequences of certain actions.

17. Commissural tracts serve as connections between the two cerebral hemispheres. Association tracts connect various regions within the same hemisphere. Projection fibers connect the cerebral hemisphere with inferior brain regions and the spinal cord.

18. Higher-order centers in the cerebral hemispheres tend to have different but complementary functions.

Cerebral lateralization refers to this specialization of the two cerebral hemispheres.

19. In most people, the left hemisphere is specialized for language abilities, and is important in performing sequential and analytical reasoning tasks, such as those required in science and mathematics. The right hemisphere is usually the seat of imagination and insight, musical and artistic skill, perception of patterns and spatial relationships, and comparison of sights, sounds, smells, and tastes.

20. Cerebral nuclei are paired irregular masses of gray matter deep within the central white matter in the basal region of the cerebral hemispheres inferior to the floor of the lateral ventricle. The nuclei include the caudate nucleus (produce a pattern and rhythm of arm and leg movements while walking), amygdala (behavioral activities, moods, expression of emotions), putamen (subconscious level of muscular movement control), globus pallidus (both excites and inhibits thalamus activities and adjusts muscle tone), and claustrum (subconscious processing of visual information).

21. The pineal gland is located in the posterior portion of the epithalamus, just superior to the corpora quadragemina. It releases the hormone melatonin and is responsible for setting circadian rhythms.

22. The thalamus is the gateway to the cerebrum. It not only routes sensory information to the correct region of the cortex, but it may also attenuate the signal, preventing the cortex from having to process extraneous signals.

23. The ventromedial nucleus of the hypothalamus monitors levels of nutrients such as glucose and amino acids in the blood and produces sensations of hunger, whereas the anterior nucleus monitors the osmolality of the blood and produces the sensation of thirst.

24. The substantia nigra produces the neurotransmitter dopamine, which affects brain processes to control movement, emotional response, and ability to experience pleasure and pain. Degeneration of neurons within the substantia nigra is part of the etiology of Parkinson’s disease.

25. The tectal plate contains paired sensory nuclei responsible for processing auditory stimuli (the inferior colliculi) and visual stimuli (the superior colliculi).

26. The pontine respiratory center is the autonomic respiratory center of the pons. It regulates skeletal muscles involved in respiration.

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27. The pyramids are located on the superior anterior surface of the medulla oblongata. They contain the corticospinal tracts of motor projection fibers, which decussate within the pyramids to provide for contralateral communication from the cerebrum to skeletal muscles.

28. Three important autonomic centers are located in the medulla oblongata: the cardiac center regulates heart rate and strength of contraction of the heart, the vasoconstriction center regulates the diameter of blood vessels and subsequently blood pressure, and the medullary respiratory center sets the basal respiratory rate.

29. The cerebellum consists of two discrete hemispheres. Each hemisphere is separated into anterior and posterior lobes by the primary fissure. The cerebellar cortex consists of folds called folia, which consist of a cerebellar cortex of gray matter, with tracts of white matter called the arbor vitae underneath.

30.

The middle cerebellar peduncles connect the cerebellum to the pons.

31. The cerebellum integrates somatic motor output from the cerebrum with proprioception and other sensory stimuli, in order to coordinate and fine-tune skeletal muscle movements. It can also store memories of previously learned movement patterns.

32. The limbic system is composed of the cingulate gyrus, parahippocampal gyrus, hippocampus, amygdaloid body, olfactory bulbs and tracts, and cortex, fornix, septal nuclei, mammillary bodies, and some thalamic nuclei.

33. The limbic system is composed of multiple cerebral and diencephalic structures that collectively process and experience emotions. The hippocampus and parahippocampal gyrus are involved in long-term memory formation and the amygdaloid body is involved in emotions such as fear. The olfactory pathways, such as the olfactory bulb, tracts, and cortex, are also associated closely with emotions, and are therefore also considered part of the limbic system.

34. The reticular activating center is the sensory component of the reticular formation of the midbrain.

It processes sensory information and adjusts the cerebral state of arousal. It is therefore associated with states of consciousness.

35. Some CNS axons remain unmyelinated and are not completely mature until the teenage years. Since a person’s ability to carry out higher-order mental functions is a direct result of the level of nervous system maturation, some forms of cortical processing are limited until after puberty.

36. An EEG may be used to evaluate sleep disorders, epilepsy and other seizure disorders, and stages of unconsciousness (e.g., if a person is in a persistent vegetative state).

37. Non-REM sleep, so named because there is no rapid eye movement, accounts for about 75% a night’s sleep and may be subdivided into 4 stages. REM sleep is where we have rapid eye movement and have our most memorable dreams. We are in REM sleep about 25% of a total night’s sleep.

38.

Cognition is defined as the collective mental processes such as awareness, knowledge, memory, perception.

39. Study methods that involve multiple repetition and assessment of the knowledge are optimum for forming long-term memories.

40. The amygdaloid body and hippocampus are responsible for developing emotional states. The prefrontal cortex, however, may override the presentation of these emotions.

41. Wernicke area is responsible for recognition of written and spoken language.

42.

The olfactory, optic, and vestibulocochlear nerves only carry sensory information.

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Answers to “Do You Know the Basics?”

1. D Feedback: The hypoglossal nerve is responsible for movement of the tongue.

2. C Feedback: The cerebellum integrates sensory information with somatic motor commands from the cerebrum, adjusting the motor commands to fine-tune movement.

3. C Feedback: The auditory association cortex is not as strongly involved in formation of long-term memories as are emotional states, repetition, or the cerebral nuclei of the limbic system.

4. D Feedback: The hypothalamus controls the autonomic nervous system, oversees the functions of the endocrine system, regulates body temperature, controls emotional behavior, controls food intake, controls water intake, and regulates the sleep/wake rhythms. It is not involved in somatic motor function.

5. C Feedback: The choroid plexus produces cerebrospinal fluid. It does not process stimuli.

6. A Feedback: The pyramids are located on the posterior of the medulla oblongata. The tegmenta are located deep within the midbrain, and the inferior colliculi are located on the posterior of the midbrain. The cerebral peduncles are located on the anterior surface of the midbrain.

7. B Feedback: The parietal lobe is located posterior to the central sulcus, and superior to the lateral sulcus.

8. A Feedback: The precentral gyrus contains the primary motor cortex.

9. B Feedback: Cerebral nuclei are clusters of unmyelinated cells deep within the white matter of the cerebrum.

10. A Feedback: The pons contains pontine respiratory centers, responsible for adjusting the respiratory rate.

11. CSF is produced by the choroid plexus within the ventricles. It flows from the lateral ventricles and third ventricle into the cerebral aqueduct and then into the fourth ventricle. Additionally, a relatively small amount of CSF from the central canal of the spinal cord travels to the fourth ventricle as well. Most of the CSF in the fourth ventricle flows into the subarachnoid space by passing through openings in its membranous roof, either the paired lateral apertures or the single median aperture. CSF flows through the subarachnoid space surrounding the brain spinal cord and nerve fibers. As additional CSF is incorporated into the subarachnoid space, one-way flaps in the arachnoid villi open into the dural venous sinuses, allowing excess CSF to be released into the venous bloodstream.

These flaps allow the CSF to be released into the blood, without allowing any venous blood to enter the subarachnoid space.

12. The primary somatosensory association area interprets information received by the primary somatosensory cortex.

13. The visual association area processes information by analyzing movement, color, and form in order to identify what is seen.

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14. Both the cerebellum and the cerebral nuclei participate in subconscious control of somatic motor movements. The cerebral nuclei, in general, remove unwanted movement from somatic motor commands, and the cerebellum integrates the motor commands with proprioception and other sensory stimuli.

15. The hypothalamus controls the autonomic nervous system, oversees the functions of the endocrine system, regulates body temperature, controls emotional behavior, controls food intake, controls water intake, and regulates the sleep/wake rhythms.

16. Stimuli resulting from pressure on the hand will enter the spinal cord where they will decussate and travel toward the brainstem, through projection tracts of white matter. In route through the medulla oblongata, the stimuli will trigger neurons in the inferior olivary nucleus, which will communicate the stimulus to the cerebellum.

Continuing on through the pons, the stimulus will reach the ventral posterior nucleus of the thalamus, from where it will be routed to the primary somatosensory cortex of the left parietal lobe.

17. The limbic system is composed of the cingulate gyrus, parahippocampal gyrus, hippocampus, amygdaloid body, olfactory bulbs and tracts and cortex, fornix, septal nuclei, mammillary bodies, and some thalamic nuclei.

18. The surgeon must cut through the skin, the external periosteum, occipital bone of the cranium, dura mater (first the periosteal layer and then the meningeal layer), the arachnoid, the pia mater, then a glial cell covering before reaching the cerebral cortex.

19. Apraxia of speech is a motor function disorder. An individual is consciously aware of what they want to say, but they are unable to coordinate and execute the motor commands needed to produce the speech. In contrast, an individual with aphasia has difficulty understanding speech or writing, or is unable to produce comprehensible speech.

20. CN II (optic) detects vision. CN III (oculomotor) innervates 4 of the 6 extrinsic eye muscles, constricts the pupil, and innervates the levator palpebrae superioris. CN IV innervates the superior oblique eye muscle, and CN VI innervates the lateral rectus eye muscle.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: The trigeminal nerve carries sensory information from the mandible and maxilla.

2. D Feedback: The trigeminal nerve also innervates the lips.

3. A Feedback: The epidural space is located between the periosteal layer of the dura mater and the skull.

4. A Feedback: The left precentral gyrus contains the primary motor cortex responsible for movement of the right arm.

5. D Feedback: The abducens nerve innervates the lateral rectus muscle which turns the eye laterally.

Answers to “Can You Synthesize What You’ve Learned?”

1. Loss of somatic motor function may be caused by damage to the primary motor cortex along the precentral gyrus of the frontal lobe. The slurred speech may indicate that the affected area also encompasses a portion anterior to the precentral gyrus, possibly including the Broca area. Because of contralateral processing, loss of function on the right side of the body would indicate that the affected area is in the left hemisphere of the brain.

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2. The blood-brain barrier would prevent the supplemented dopamine from entering the nervous system. Nervous tissue is isolated from the general circulation by the blood-brain barrier, which strictly regulates which substances can enter the brain. The advantage of the blood-brain barrier is that it helps prevent exposure of neurons in the brain to drugs, waste products in the blood, and variations in levels of normal substances such as hormones.

3. Dustin is more likely to survive damage to the cerebrum than the medulla oblongata. The cerebral cortex manages memories as well as somatic sensory and motor processing, some of which, although important, are not deadly if damaged. The medulla oblongata, however, controls multiple autonomic functions necessary for maintaining homeostasis, which cannot be interrupted.

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Chapter 14 Answers to “What Did You Learn?”

1. The cervical and lumbosacral enlargements are portions of the spinal cord that are wider/larger than the rest of the spinal cord. These enlargements contain motor neurons that innervate the upper and lower limbs, respectively – and since there are more motor neurons needed to innervate these large areas, these portions of the spinal cord are larger.

2. There are 31 pairs of spinal nerves: 8 cervical (C1–C8), 12 thoracic (T1–T12), 5 lumbar (L1–L5), 5 sacral (S1–S5), and 1 coccygeal (Co1) nerve.

3. The epidural space lies between the dura mater and the inner walls of the vertebrae (that surround the vertebral foramen). The subdural space is a potential space between the arachnoid mater and dura mater. The subarachnoid space lies between the pia mater and arachnoid mater, and it contains the cerebrospinal fluid (CSF).

4. The anterior horns of gray matter contain the cell bodies of somatic motor neurons, whereas the lateral horns of gray matter house cell bodies of autonomic motor neurons. The posterior horns of gray matter contain axons of sensory neurons as well as cell bodies of interneurons.

5. The three types of funiculi are anterior, lateral and posterior and are composed of white matter. The anterior and lateral funiculi contain both ascending (sensory) and descending (motor) tracts. The posterior funiculi contain ascending (sensory) tracts only.

6. The four characteristics common to all nervous system pathways include general location of neuron components, they are composed of two or more neurons, they are paired, and most pathways decussate (cross over) to the opposite side of the body.

7. Sensory pathways use a series of two or three neurons to transmit nerve signals from the body to the brain.

(1) The first neuron is the primary neuron. Its cell body resides in the posterior root ganglia of spinal nerves. It transmits nerve signals from the receptor to the secondary neuron. (2) The second neuron is an interneuron within the spinal cord that extends to and transmits nerve signals from the primary neuron to either the tertiary neuron or to the cerebellum. (3) The third neuron is an interneuron within the cerebrum (specifically the primary somatosensory cortex of the parietal lobe). Pathways that lead to the cerebellum do not have a tertiary neuron.

8. The posterior funiculus-medial lemniscal pathway conducts sensory stimuli concerned with proprioceptive (posture and balance) information about limb position and discriminative touch, precise pressure, and vibration sensations.

9. The secondary neurons of the anterior and lateral spinothalamic tracts originate in the posterior horn of the spinal cord. The axons of the secondary neurons in the anterior spinothalamic tracts are located in the anterior funiculi, while the axons of the secondary neurons in the lateral spinothalamic tracts are located in the lateral funiculi.

10. Upper motor neurons are housed within the cerebral cortex or a brainstem nucleus, and they synapse either directly on lower neurons in the brainstem or spinal cord or on interneurons that synapse directly on lower motor neurons. Axons of lower neurons (either within a brainstem cranial nerve nucleus) exit the CNS and project to the skeletal muscles to be innervated and then conduct the commands out of the CNS. The upper motor neurons may be either stimulatory or inhibitory, whereas the lower neurons are only excitatory.

11. The direct pathway originates in the primary motor cortex. Axons from neurons in this pathway extend from the cerebral cortex and synapse on neurons either in the brainstem (corticobulbar tracts) or in the spinal cord (corticospinal tracts). They innervate skeletal muscle. The indirect pathway has upper motor neurons

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that originate within brainstem nuclei and take a complex, circuitous route through the brain before conducting the nerve signal to the spinal cord. It modifies or helps control the pattern of somatic motor activity by exciting or inhibiting the lower motor neurons that innervate the muscles.

12. Both anterior and posterior rami contain motor and sensory axons. A posterior ramus innervates the deep back muscles and receives sensations from the skin of the back, posterior of the neck, and posterior aspect of the head. The much-larger anterior ramus innervates muscles and receives sensations from the anterior and lateral parts of the neck, anterior and lateral parts of the torso, pelvis and perineum, and upper and lower limbs.

13. A dermatome is a segment of skin supplied by a single spinal nerve. They are clinically significant because a) they may help indicate damage to a specific spinal nerve, or b) be a source of referred visceral pain (where discomfort from an internal organ is mistakenly referred or felt in a dermatome).

14. A typical nerve plexus consists of a network of interweaving anterior rami of spinal nerves. The neurons from one ramus may contribute to multiple nerves, and a single named nerve may consist of neurons originating at numerous levels along the spinal cord.

15. Intercostal nerves innervate the anterior and lateral thoracic wall, a proximal medial part of the upper limb, and the superior aspect of the anterior and lateral abdominal wall.

16. The phrenic nerve innervates the thoracic diaphragm.

17. The anterior rami of C5-T1 typically compose the brachial plexus.

18. You likely damaged the axillary nerve, as this nerve innervates the deltoid muscle and also transmits sensory information from the superolateral aspect of the arm.

19. The ulnar nerve innervates 1 and 1/2 anterior forearm muscles and most of the intrinsic hand muscles. It receives sensory nerve signals from the skin of the dorsal and palmar aspects of the pinky finger and the medial half of the ring finger. The radial nerve innervates the posterior muscles of the arm and forearm. It receives sensory nerve signals from the posterior arm and forearm surface and the dorsolateral side of the hand.

20. The femoral nerve innervates the quadriceps femoris. Thus, damage to the nerve may result in difficulty in extending the knee.

21. The sacral plexus is formed from the anterior rami of L4–S4, and innervates the gluteal region, pelvis, perineum, posterior thigh, and almost all of the leg and foot.

22. All reflexes have four common properties: (1) A stimulus is required to initiate a response to sensory input, (2) a rapid response requires that few neurons are involved and synaptic delay is minimal, (3) a preprogrammed response occurs the same way every time, and (4) an involuntary response requires no conscious intent or pre-awareness of the reflex activity.

23. The five steps in a reflex arc are as follows: (1) A stimulus activates a receptor; (2) the sensory neuron transmits a nerve signal to the spinal cord; (3) information from the nerve signal is processed in the integration center by interneurons; (4) the motor neuron transmits a nerve signal to an effector; and (5) the effector responds to the nerve signal from the motor neuron.

24. A monosynaptic reflex has only a sensory neuron and motor neuron. The sensory axons synapse directly on the motor neurons, whose axons project to the effector. There is only one synapse with only one synaptic delay.

In contrast, a polysynaptic reflex has one (or more) interneurons positioned between the sensory and motor neuron.

Thee reflex arcs are more complicated and not as rapid.

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25. The four common spinal reflexes are the stretch reflex, Golgi tendon reflex, withdrawal reflex, and crossedextensor reflex.

26. The Golgi tendon reflex is a) spinal, b) somatic, c) polysynaptic and d) ipsilateral.

27. A hypoactive reflex, where a reflex response is diminished or absent, may indicate damage to a specific segment of the spinal cord, muscle disease, or damage to a neuromuscular junction.

28. The alar plates form the posterior horns and the posterior half of the gray commissure, while the basal plates form the anterior horns, lateral horns, and the anterior half of the gray commissure.

Answers to “Do You Know the Basics?”

1. A Feedback: The arachnoid mater lies just deep to the subdural space.

2. D Feedback: The anterior root of a nerve contains only the axons of motor neurons (the cell bodies of the motor neurons reside in the anterior horn of the spinal cord). The posterior root contains only sensory neurons.

3. C Feedback: Tertiary neurons are interneurons and their cell bodies reside within the thalamus. Their axons project to the primary somatosensory cortex.

4. B Feedback: The spinocerebellar tract carries sensory information to the cerebellum.

5. B Feedback: The radial, ulnar, axillary, median, and musculocutaneous nerves originate from the brachial plexus.

6. B Feedback: The posterior ramus provides innervation to the deep muscles of the back and the skin of the back.

7. C Feedback: Intercostal nerves originate from between thoracic vertebrae, and innervate intercostal muscles as well as the skin of the thorax, axilla, and the medial aspect of the arm.

8. A Feedback: The femoral nerve innervates the anterior thigh muscles and skin on the anterior thigh.

9. D Feedback: A stretch reflex is a monosynaptic response to stretching of a muscle which causes the muscle to contract.

10. B Feedback: A hypoactive reflex may indicate damage to a segment of the spinal cord, or it may suggest muscle disease or damage to the neuromuscular junction.

11. The spinal cord is subdivided into five parts. From superior to inferior these are: cervical, thoracic, lumbar, sacral, and coccygeal. There are 31 pairs of spinal nerves, and they are named after the vertebrae forming the inferior portion of the intervertebral canal through which they pass. For example, the nerve passing in between vertebrae C2 and C3 would be C3, the third cervical spinal nerve. The nerve exiting the spinal cord in between C7 and T1 is an exception, as it is called C8. Nerves C1 through C8 originate at the cervical level of the spinal cord, T1 through T12 originate at the thoracic level, L1 through L5 originate at the

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lumbar level, S1 through S5 originate at the sacral level, and the coccygeal nerve originates at the coccygeal level of the spinal cord.

12. The anterior horn of gray matter contains the cell bodies of somatic motor neurons and the lateral horn houses cell bodies of autonomic motor neurons. The posterior horn contains axons of sensory neurons as well as cell bodies of interneurons.

13. The posterior funiculus-medial lemniscal pathway conducts sensory stimuli concerned with proprioceptive (posture and balance) information about limb position and discriminative touch, precise pressure, and vibration sensations. The anterolateral pathway conducts nerve signals related to crude touch and pressure as well as pain and temperature.

14. Upper motor neurons are housed either within the cerebral cortex or a nucleus in the brainstem. Their axons synapse with lower neurons housed either within the anterior horn of the spinal cord or within a brainstem cranial nerve nucleus. Axons from the lower neurons then conduct the commands out of the CNS. The upper motor neurons may either excite or inhibit the activity of lower motor neurons, whereas the lower neurons are always excitatory.

15. The axillary nerve innervates the deltoid and teres minor muscles. The median nerve innervates most of the anterior muscles of the forearm, thenar muscles, and the lateral two lumbricals. The musculocutaneous nerve innervates the coracobrachialis, biceps brachii, and brachialis muscles. The radial nerve innervates the posterior arm and forearm muscles, and the brachioradialis muscle. The ulnar nerve innervates the anterior forearm muscles and the intrinsic muscles of the hand.

16. The lumbar plexuses are formed from the anterior rami of spinal nerves L1–L4, and innervate muscles and dermatomes of the anterior and superomedial aspects of the thigh, lower anterior leg, and medial foot.

17. The tibial nerve innervates posterior thigh and leg muscles, and plantar foot muscles. The common fibular nerve innervates the short head of the biceps femoris.

18. The five steps in a reflex arc are: (1) a stimulus activates a receptor, (2) a nerve impulse travels through a sensory neuron to the CNS, (3) information from the nerve signal is processed in the integration center by interneurons, (4) a motor neuron transmits a nerve signal to an effector, and (5) the effector responds to the nerve signal from the motor neuron.

19. A stretch reflex is a monosynaptic response that contracts a muscle in response to stretching of the muscle.

A Golgi tendon reflex is a polysynaptic process that lengthens and/or relaxes muscles in response to increased tension.

20. The basal plates lie anterior to the sulcus limitans. They develop into the anterior and lateral horns, motor structures of the gray matter, and the anterior part of the gray commissure of the spinal cord. The alar plates lie posterior to the sulcus limitans. They develop into posterior horns, sensory structures of the gray matter, and the posterior part of the gray commissure.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: The ulnar nerve descends along the medial side of the arm. It travels posterior to the medial epicondyle of the humerus and then runs along the ulnar side of the forearm.

2. C Feedback: The ulnar nerve innervates the anterior forearm muscles and the intrinsic hand muscles.

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3. A Feedback: The ulnar nerve innervates the anterior forearm muscles and the intrinsic hand muscles, including the adductor pollicis.

4. A Feedback: The sacral plexus consists of anterior roots from spinal nerves L4–S4. A herniated disk in the lumbar region could put pressure on the roots contributing to the sciatic nerve which innervates the posterior aspect of the leg, thereby causing pain.

5. D Feedback: The superficial fibular nerve innervates lateral compartment muscles of the leg (foot evertors and plantar flexors).

Answers to “Can You Synthesize What You’ve Learned?”

1. Arthur injured his spinal column at the cervical level. Although he may regain partial function of nerves originating at this level once the inflammation associated with the injury subsides, he is unlikely to regain complete function if the spinal cord was permanently injured.

2. The common fibular nerve may have been injured by the break of the fibula or because of too much pressure from the cast. The anterior and lateral leg muscles would have been affected, leaving her unable to dorsiflex or evert the foot.

3. The piece of glass elicited a withdrawal reflex of her foot, which was accompanied by a cross-extensor reflex to help her maintain balance. The withdrawal reflex causes the one lower limb to flex at the knee, due to contraction of hamstring muscles. In contrast, the crossed-extensor reflex stimulates the quadriceps femoris muscle to contract on the other limb, so that it remains extended and supports her body weight.

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Chapter 15 Answers to “What Did You Learn?”

1. The somatic nervous system [SNS] includes processes that are achieved or controlled consciously, whereas the autonomic nervous system [ANS] includes processes that are regulated below the conscious level. The SNS has a somatic sensory portion and a somatic motor portion that involves initiation and transmission of nerve signals from the CNS to control skeletal muscles. The ANS is a motor system only. Its components initiate and transmit nerve signals from the CNS to cardiac muscle, smooth muscle, and glands. It often responds to input from visceral sensory components but these structures are not part of the ANS. 2. A single lower motor neuron extends from the CNS to skeletal muscle fibers in the somatic nervous system. It is large in diameter and myelinated. In comparison, a chain of two lower motor neurons extends from the CNS to innervate cardiac muscle, smooth muscle, and glands in the ANS. The first neuron is the preganglionic neuron.

Its cell body lies within the brainstem or spinal cord. A preganglionic axon extends from this cell body and exits the CNS in either a cranial nerve or spinal nerve. The axon projects to an autonomic ganglion in the peripheral nervous system. The axon is myelinated and typically small in diameter. The second neuron is called a ganglionic neuron. Ganglionic neurons have unmyelinated axons that are smaller in diameter than preganglionic axons.

3. The hypothalamus is the integration and command center for autonomic function.

4. The parasympathetic division functions to maintain homeostasis when we are at rest. It is primarily concerned with conserving energy and replenishing nutrient stores.

5. Parasympathetic pathways originate either in the brainstem or in the S2–S4 regions of the spinal cord.

Sympathetic pathways originate in the lateral horns of the T1-L1 spinal cord segments. Parasympathetic preganglionic axons are long, myelinated, and have relatively few branchings. Parasympathetic postganglionic axons are short and unmyelinated. Sympathetic preganglionic axons are short, myelinated, and have numerous branchings. Sympathetic postganglionic axons are long and unmyelinated. Parasympathetic autonomic ganglia are either close to or within the effector (and called terminal ganglia or intramural ganglia). Sympathetic autonomic ganglia are relatively close to the spinal cord and are on either side of the spinal cord or anterior to the spinal cord.

6. The parasympathetic response tends to be discrete and localized, while the sympathetic response often (but not always) results in mass activation, in which multiple structures are stimulated simultaneously.

7. The cranial nerves containing neurons from the parasympathetic division are the oculomotor nerve (CN III), facial nerve (CN VII), glossopharyngeal nerve (CN IX), and vagus nerve (CN X). The oculomotor nerve innervates the eye (ciliary muscles to control lens for accommodation and sphincter papillae to constrict the pupil). The facial nerve innervates the lacrimal gland, the sublingual and submandibular salivary glands, and several other small glands of the oral and nasal cavities. The glossopharyngeal nerve innervates the parotid salivary gland. The vagus nerve innervates the viscera of the thoracic cavity (heart, lungs, and trachea) and the abdominal cavity (liver, gallbladder, stomach, spleen, pancreas, kidneys, ureters, small intestine, and the proximal portion of the large intestine).

8. The pelvic splanchnic nerves innervate some organs of the abdominal cavity (the distal part of the large intestine) and most organs of the pelvic cavity (the rectum, urinary bladder, distal part of the ureter, and most reproductive organs).

9. Sympathetic trunk ganglia are part of the sympathetic trunks which are located lateral to each side of the vertebral column. The prevertebral ganglia are located (1) anterior to the vertebral column on the anterolateral surface of the aorta and (2) only in the abdominopelvic cavity.

10. White rami carry myelinated preganglionic sympathetic axons from T1 to L2 nerves to the sympathetic trunk.

Because the axons are myelinated the rami have a whitish appearance. Gray rami carry postganglionic sympathetic

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11. axons from the sympathetic trunk to the spinal nerve. The postganglionic axons are unmyelinated, so these rami have a grayish appearance. They connect to all spinal nerves.

12. The spinal nerve pathway innervates integumentary structures, while the splanchnic nerve pathway innervates abdominal and pelvic viscera. The spinal nerve pathway has a preganglionic neuron that synapses with a ganglionic neuron in a sympathetic trunk ganglion. The postganglionic axon travels through a gray ramus that is at the same ‘level’ as the ganglionic neuron and then it enters the spinal nerve and extends to its target organ. In the splanchnic nerve pathway, a preganglionic neuron does not synapse with a ganglionic neuron in a sympathetic trunk ganglion. Instead, the preganglionic axons that pass through the sympathetic trunk ganglia without synapsing extend to the prevertebral ganglia. There, the preganglionic axon synapses with a ganglionic neuron whose axon then travels to the effector organs.

13. The adrenal medulla is directly innervated by preganglionic sympathetic axons. Stimulation of neurosecretory cells here causes the release of epinephrine and norepinephrine. These hormones circulate within the blood and help prolong the effects of sympathetic stimulation.

14. Cholinergic neurons include all sympathetic and parasympathetic preganglionic neurons, all parasympathetic ganglionic neurons, and specific sympathetic ganglionic neurons that innervate sweat glands of the skin and blood vessels in skeletal muscle tissue. All other sympathetic ganglionic neurons are adrenergic.

15. Nicotinic receptors are located on the cell bodies of ganglionic neurons and cells of the adrenal medulla.

Muscarinic receptors are located on plasma membranes of target cells in the parasympathetic division as well as some sympathetic pathways, such as those that innervate sweat glands and blood vessels in the skeletal muscle.

16. Binding of neurotransmitters to nicotinic receptors opens sodium ion channels, allowing more positive ions to enter the cell, generating an excitatory postsynaptic potential.

17. The different types of catecholamines include: dopamine, epinephrine, and norepinephrine.

18. Activation of α1 adrenergic receptors stimulates smooth muscles, causing vasoconstriction. Stimulation of β2 adrenergic receptors causes relaxation of smooth muscle, causing vasodilation.

19. A decrease in stimulation below the sympathetic tone causes vessel dilation, whereas an increase in stimulation above sympathetic tone causes vessel constriction.

20. Sympathetic stimulation increases heart rate and force of contraction, whereas parasympathetic stimulation decreases heart rate.

21. The male penis becomes erect as a result of parasympathetic innervation, and ejaculation of semen from the penis is facilitated by stimulation from the sympathetic division.

22. Smooth muscle in blood vessels, sweat glands, arrector pili muscles in the skin, and neurosecretory cells of the adrenal medulla are stimulated by sympathetic pathways only.

23. Autonomic plexuses are collections of sympathetic postganglionic axons and parasympathetic preganglionic axons, as well as some visceral sensory axons.

24. When blood pressure rises, stretch receptors in the blood vessel walls are stimulated and nerve signals are sent to the cardiac center in the medulla oblongata. As a result, sympathetic output is inhibited and parasympathetic output to the heart is stimulated, so as to slow heart rate and decrease blood ejection from the heart. The end result is a decrease in blood pressure.

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Answers to “Do You Know the Basics?”

1. C Feedback: Splanchnic nerves are preganglionic axons that leave the sympathetic trunk ganglia, without synapsing, and extend to prevertebral ganglia.

2. B Feedback: Parasympathetic pathways originate in the brainstem and S2–S4 regions of the spinal cord.

3. C Feedback: The parasympathetic division of the ANS is responsible for increasing gastric motility and digestion.

4. A Feedback: Autonomic tone is the maintenance of some continual activity by the ANS. 5. D Feedback: White rami transmit myelinated preganglionic axons to the sympathetic trunk.

6. B Feedback: Acetylcholine is released by all parasympathetic axons, all preganglionic sympathetic axons, and a few postganglionic sympathetic axons.

7. C Feedback: The hypogastric plexus innervates pelvic organs.

8. A Feedback: Sympathetic pathways have short, myelinated preganglionic fibers, while their postganglionic fibers are long and unmyelinated.

9. A Feedback: Nicotinic receptors are located on the cell bodies of all ganglionic neurons and cells of the adrenal medulla.

10. D Feedback: β receptors are adrenergic and bind epinephrine or norepinepherine. β1 receptors in the heart increase heart rate and force of contraction.

11. The three CNS regions that regulate autonomic function are the hypothalamus, brainstem, and spinal cord.

12. The sympathetic trunk ganglia are immediately lateral to the vertebral column (on both sides) and are a part of the sympathetic division. The prevertebral ganglia are clusters of sympathetic division neuron cell bodies of ganglionic neurons located anterior to the vertebral column on the anterolateral wall of the abdominal aorta at the base of major abdominal arteries. The terminal ganglia are a collection of parasympathetic division neuron cell bodies of ganglionic neurons located very close to the target organ.

13. Parasympathetic postganglionic fibers are relatively shorter, unmyelinated, and release acetylcholine.

Sympathetic postganglionic fibers are relatively longer, unmyelinated, and either release the neurotransmitter norepinepherine (most postganglionic axons) or acetylcholine (a few specific axons).

14. Sympathetic innervation inhibits peristalsis (motility), inhibits GI tract gland secretion, closes GI tract sphincters and stimulates glycogenolysis from the liver. Parasympathetic innervation stimulates gastric motility, opens GI tract sphincters, stimulates GI tract gland secretion, and stimulates glycogenesis in the liver.

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15. Acetylcholine opens ion channels within nicotinic receptors, depolarizing the cell membrane and always generating an EPSP. Acetylcholine affects cells possessing muscarinic receptors through second messengers, either stimulating the specific target cell or inhibiting the specific target cell.

16. Cooperative effects are seen when both parasympathetic and sympathetic stimulation cause different effects that together produce a single, distinct result. Antagonistic interactions are seen when the two branches of the ANS have opposing effects on the same target.

17. The general functions of the sympathetic division are concerned with “fight-or-flight”, because it prepares the body for emergencies by increasing alertness and metabolic activity needed to coordinate and direct body response in stressful or frightening situations. The parasympathetic division is primarily involved with maintaining the body’s internal environment (homeostasis) and has been nicknamed the “rest-and-digest” system, because it concerns itself with conserving energy and replenishing nutrient stores.

18. Mass activation is an important response to stress when you are scared or exercising: it increases heart rate and blood pressure, increases depth and rate of breathing, dilation of pupils, and mobilization of energy reserves from the liver.

19. Baroreceptors in the bladder wall are stretched when the bladder fills. Nerve signals (in a toilet trained individual) are transmitted along sensory neurons to the pons. The reflex results in the contraction of the smooth muscle in the bladder wall and relaxation of the urinary sphincters following voluntary relaxation of the external urethral sphincter.

20. A decrease in stimulation below the sympathetic tone causes vessel dilation, whereas an increase above sympathetic tone causes vessel constriction.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: A sympathetic response would cause pupil dilation, not pupil constriction.

2. A Feedback: Release of epinephrine and norepinephrine from the adrenal medulla is part of the sympathetic response to possible danger and they potentiate the continued level of response.

3. A Feedback: A beta blocker would inhibit sympathetic stimulation to the heart, thus decreasing heart rate.

4. D Feedback: Albuterol would bind to β2 adrenergic receptors, causing a decrease in stimulation of smooth muscle.

5. B Feedback: Decreased parasympathetic stimulation would decrease secretion of HCl from gastric glands.

Answers to “Can You Synthesize What You’ve Learned?”

1. The sympathetic nervous system provides a capacity to quickly respond to a dangerous situation, quickly adjusting physiological functions.

2. Decreased blood flow to skeletal muscles may occur because the body is also routing increased blood flow to the digestive system.

3. The parasympathetic pathways are activated in response to the need for digestion: it is called the ‘rest-anddigest’ system. Thus, the body is replenishing nutrient stores and at the same time feeling sleepy and less attentive to lecture.

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Chapter 16 Answers to “What Did You Learn?”

1. A sensory receptor is a component of our nervous system that responds to an external or internal stimulus and initiates sensory input to the central nervous system. This involves converting the stimulus energy into an electrical signal. The original energy form detected must be changed (transduced) into electrical energy that is conducted along a sensory neuron.

2. Sensory receptors range in complexity from the relatively simple, bare terminal ending of a single sensory neuron (e.g., some touch receptors) to complex structures called sense organs whose nerve endings are associated with epithelial tissue, connective tissue, or muscular tissue (e.g., the eye). All sensory receptors have a receptive field, which is the amount of area through which a sensory receptor will detect a stimulus. The size of a receptive field varies and determines the ability of the CNS to identify the exact location of a stimulus.

3. Sensory input is relayed from receptors to the CNS for interpretation. The sensory information has several characteristics that are interpreted by the CNS: (1) the modality (or form of the stimulus) is determined by the specific sensory neurons that relay nerve signals to specific regions of the CNS; (2) the location of the stimulus is determined by nerve signals arriving to specific regions of the CNS (these arrive from designated sensory neurons within a given nerve); (3) the intensity of the stimulus is determined by the number of nerve signals received in the CNS (the more intense the stimulus, the greater the number of nerve signals that are initiated and relayed to the CNS); and (4) the duration of the stimulus is determined by a progressive decrease in frequency of nerve signals over time.

4. The classification criteria for receptors include: receptor distribution, stimulus origin, and modality of stimulus. a) The cochlea within the inner ear (and the sense of hearing) is a special sense because the cochlea is located in the head (receptor distribution), it is an exteroceptor because it detects stimuli outside the body (stimulus origin), and it is a mechanoreceptor because it responds to distortion of the plasma membrane that occurs due to movement of hair cells in the cochlea in response to sound waves. b) The taste buds of the tongue (and the sense of taste) are a special sense because the tongue is located in the head (receptor distribution), they are exteroceptors because they detect stimuli outside the body (stimulus origin), and they are chemoreceptors because they respond to molecules and ions in the food that we eat. c) Stretch receptors in the bladder wall correspond to a general sense because they are not located in the head (receptor distribution), they are interoceptors because they detect stimuli within the body (stimulus origin), and they are mechanoreceptors because they respond to distortion of the plasma membrane that occurs due to stretch of the bladder wall.

5. Unencapsulated receptors are: (1) Free nerve endings located in the papillary layer of the dermis with some branches of the nerve endings extending into the epidermis; (2) Root hair plexuses located in the reticular layer of the dermis; and (3) Tactile discs located within the stratum basale of the epidermis.

6. Referred pain occurs when sensory nerve signals from certain viscera are perceived as originating not from the organ, but from somatic sensory receptors within the skin and skeletal muscle. Numerous cutaneous and visceral sensory neurons conduct nerve signals on the same ascending tracts with the spinal cord. As a result, the somatosensory cortex in the brain is unable to accurately determine the actual source of the stimulus, thus the stimulus may be localized incorrectly. For example, pain associated with a myocardial infarction may be referred to the skin dermatomes innervated by the T1–T5 spinal nerves, which lie along the pectoral region and the medial side of the arm.

7. Odorant (volatile) molecules must first dissolve in the mucus lining the olfactory mucosa in the nasal cavity to be detected by chemoreceptors.

8. Sensory input from the olfactory mucosa regarding the sense of smell is often transmitted to the amygdala, a component of the limbic system.

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9. Taste buds are located on the fungiform, vallate, and foliate papillae, but primarily on the vallate papillae.

They are onion-shaped sensory organs containing taste receptors. Taste buds are composed of three distinct cell types: (1) Gustatory cells which detect tastants (taste-producing molecules) in our food, (2) Supporting cells that sandwich between the gustatory cells and sustain the receptors, and (3) Basal cells that function as neural stem cells to continually replace the relatively short-lived gustatory receptor cells.

10. The five basic taste sensations are: sweet, salt, sour, bitter, and umami. Sweet tastes are produced by organic compounds (e.g., sugars or artificial sweeteners), salty tastes are elicited by metal ions (e.g., sodium or potassium ions), sour tastes are associated with hydrogen ions, bitter tastes are produced by alkaloids, and the umami taste is generated by amino acids such as glutamate or aspartate.

11. The conjunctiva is a specialized stratified squamous epithelium that forms a continuous transparent lining over the external, anterior surface of the eye (except it does not cover the cornea) and is folded to also cover the internal surface of both eyelids. It lubricates and moistens the eye, supplies nutrients to the sclera of the eye (through its many blood vessels), and has sensory nerve endings that detect foreign objects contacting the eye.

12. (a) A lacrimal gland continuously produces lacrimal fluid (tears). (b) Lacrimal fluid is spread across the eye surface when we blink. (c) The fluid enters the lacrimal puncta, then drains into the lacrimal canaliculi and collects in the lacrimal sac. (d) Lacrimal fluid then drains through the nasolacrimal duct and enters the nasal cavity.

13. a) The fibrous tunic is the external layer of the eye wall composed of the posterior sclera and anterior cornea.

The sclera provides for eye shape and protects its delicate internal components, while the cornea refracts incoming light rays into the interior of the eye. b) The vascular tunic, the middle layer of the eye wall, is composed of three distinct regions: the choroid, the ciliary body, and the iris (from posterior to anterior). (1) The choroid is composed of connective tissue that houses both a capillary network that supplies nutrients and oxygen to the retina and melanocytes that produce pigment that absorbs excess light. (2) The ciliary body is composed of both ciliary muscles (smooth muscle bands) that function in lens shape change for near and far vision and ciliary processes (containing capillaries). The ciliary process forms aqueous humor, which circulates through the anterior cavity of the eye. (3) The iris is the colored portion of the eye. In its center is an opening, called the pupil. The iris has two layers of smooth muscle fibers, melanocytes, and an array of vascular and nervous structures. The iris controls pupil size or diameter and thus the amount of light entering the eye using its two smooth muscle layers. c) The internal tunic is called the retina. It is composed of an outer pigmented layer and an inner neural layer.

The pigmented layer absorbs light rays that pass through the inner layer. The neural layer houses all of the photoreceptors and their associated neurons. This layer is responsible for detecting light rays and converting them into nerve signals that are transmitted to the brain.

14. The cornea is a convex, transparent structure that forms the anterior one-sixth of the fibrous tunic. It is composed of an inner simple squamous epithelium, a middle layer of collagen fibers, and an outer stratified squamous epithelium called the surface corneal epithelium. The cornea contains no blood vessels. Nutrients and oxygen are supplied to the inner simple squamous epithelium by aqueous humor within the anterior cavity, whereas the surface corneal epithelium receives its oxygen and nutrients from lacrimal fluid. The lens is a strong, deformable, transparent structure. It is composed of precisely arranged layers of cells which have lost their organelles, are filled completely by a protein called crystallin, and which are bounded by a dense, fibrous, elastic capsule. The circulation of aqueous humor through the posterior chamber, pupil, and anterior chamber provides nutrients and oxygen to the lens.

15. Vitreous humor is the transparent, gelatinous fluid that completely fills the posterior cavity of the eye. It is a permanent fluid produced during embryological development and both helps maintain eye shape and supports the retina to keep it flush against the back of the eye. The aqueous humor is a transparent watery fluid that circulates within the anterior cavity of the eye. It is continuously produced by the ciliary process and drained via the scleral venous sinus. The circulation of aqueous humor provides nutrients and oxygen to both the cornea (inner epithelium) and lens, which are both avascular structures.

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16. The eyes are converging. The ciliary muscles are contracted and the lens is curved so the light is refracted to a greater extent (i.e., there is accommodation). The pupil is relatively constricted to allow a lesser amount of light into the eye.

Light rays are refracted (bent) when (a) they pass between two media of different densities, and (b) those media meet at a curved surface. Before light can reach photoreceptors in the retina it must pass from air through the cornea, the aqueous humor, the lens, and the vitreous humor as well as through the inner layers of neurons in the retina to reach photoreceptors. Refraction of light for vision is greatest as light rays pass from air into the cornea, because their difference in refractive index is maximal. Although the shape of the cornea cannot be altered, lens shape is changeable to focus light rays onto the retina.

17. Rods and cones both have inner segments containing most of the cellular machinery and outer segments composed of multiple photoreceptor-containing discs embedded within the epithelium of the pigmented layer of the retina. Structurally, rods are longer and narrower than cones and they contain the photopigment rhodopsin, which is optimized for detecting low levels of light at a wavelength of approximately 500 nm. In contrast, cones have outer segments that are both shorter than those of rods and also conically shaped. Their outer-segment discs contain one of three photopigments called photopsins, which are specialized for transducing colors under bright light.

18. Dark adaptation occurs as rods are bleached from exposure to bright light and require time to regenerate rhodopsin. Light adaptation is the process by which your eyes adjust from low light to bright light conditions.

Even though your pupils constrict to reduce the amount of light entering your eyes, you are temporarily blinded as the rods become inactive and the cones, which were initially overstimulated, gradually adjust to the brighter light.

19. Phototransduction is converting (or transducing) light energy into an electrical signal. Photoreceptor cells (rods and cones) are the specific cells within the neural layer of the retina that engage in phototransduction.

In the dark, the outer segments of photoreceptor cells continuously produce cyclic GMP (cGMP) from guanosine triphosphate (GTP) catalyzed by the enzyme guanylate cyclase. cGMP binds to cation channels in the plasma membrane of the outer segment, allowing an influx of both Na+ and Ca2+. This influx of cations (called the dark current) depolarizes the photoreceptor cells to about -40 mV. These local currents of ions diffuse from the outer segments, reaching voltage-gated Ca2+ channels at the synaptic terminals of the photoreceptor cells; this change in voltage triggers these channels to open. Calcium ions enter the synaptic terminals, triggering the continuous (tonic) release of glutamate neurotransmitter. Glutamate binds with receptors of the bipolar cells to cause hyperpolarization of these cells, which prevents them from releasing neurotransmitters from their synaptic terminals.

In the light, rhodopsin bleaches, leading to a decrease in cGMP. The decrease in cGMP levels closes cation channels. There is a subsequent inhibition of glutamate release. The bipolar cell is no longer inhibited; thus, it depolarizes and releases neurotransmitter. The neurotransmitter stimulates the ganglion cell and a nerve signal (action potential) is initiated and transmitted to the brain.

20. The conscious perception of visual stimuli occurs in the thalamus (lateral geniculate nucleus) and the visual cortex in the occipital lobe. Reflexive responses occur in the superior colliculi.

21. Axons from each cranial nerve cross over to the opposite hemisphere of the brain, ensuring that each hemisphere receives visual information from both eyes so there will be overlapping images formed to create stereoscopic vision or depth perception.

22. The external acoustic meatus conducts sound waves to the tympanic membrane, while preventing entry of foreign objects.

23. Auditory ossicles (the malleus, incus, and stapes) are located in the middle ear between the tympanic membrane and the oval window. They amplify sound waves from the tympanic membrane to the oval window.

24. The bony labyrinth is structurally and functionally partitioned into three regions: the cochlea, the vestibule and the semicircular canals. The membranous labyrinth is formed by membrane-lined, fluid-filled tubes within the

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bony labyrinth, including: the cochlear duct within the cochlea, the utricle and saccule within the vestibule, and the semicircular duct within the semicircular canals.

25. Steps for detecting sounds are as follows: (1) Sound waves are collected by the auricle and funneled through the external auditory canal to make the tympanic membrane vibrate. (2) The vibration of the tympanic membrane causes movement in the auditory ossicles (the malleus, incus, and stapes). (3) The foot of the stapes vibrates, moving like a piston on the oval window and causing pressure waves in the perilymph fluid of the inner ear. (4) Pressure waves travel through the perilymph in the scala vestibuli. (5) Pressure waves cause the vestibular membrane to vibrate, resulting in pressure wave formation in the endolymph of the cochlear duct. (6) Pressure waves in the cochlear duct displace a specific region of the basilar membrane, causing distortion of stereocilia on hair cells of the spiral organ. This distortion causes a stimulus in the cochlear nerve. Remaining pressure waves are transferred to the perilymph of the scala tympani and are absorbed at the round window.

26. Pitch is dependent upon the frequency of the vibrating object. Frequency is the rate of back and forth motion of the vibrating object and it is measured in cycles/second. Different regions of the basilar membrane move in response to the frequency of the sound waves. Loudness is dependent upon the amount of back and forth motion of the vibrating object that establishes the degree of compression of the molecules (amplitude of sound waves). Intensity refers to a sound’s loudness. Louder sounds cause greater movement of the basilar membrane, which increases the number of nerve signals relayed to the brain.

27. Auditory stimuli from the cochlear nerve terminate in the cochlear nucleus within the medulla oblongata.

Secondary neurons then conduct the information simultaneously to the inferior colliculus in the midbrain and to the superior olivary nuclei within the pons (from which it is then relayed to the inferior colliculus). Within the inferior colliculus, startle reflexes in response to loud sound may be initiated, prior to transmitting the nerve signals to the medial geniculate nucleus of the thalamus for initial processing and filtering of auditory sensory information. After attenuation of the signal within the thalamus, tertiary neurons conduct the signal to the primary auditory cortex within the temporal lobe, where perception of sound occurs.

28. The maculae detect static equilibrium (when the head is stationary) and linear dynamic equilibrium. Tilting of the head causes the otolithic membrane to shift its position on the macula surface, thus distorting the stereocilia.

29. The ampullae associated with the semicircular canals detect angular acceleration (i.e., when the head is rotated). As the head rotates, endolymph within the corresponding canal lags behind, putting pressure on the cupula. Bending of the cupula causes a deflection of stereocilia, which in turn results in a change in the amount of neurotransmitter released from the hair cells, and a simultaneous change occurs in the stimulation of the sensory neurons of the vestibular branch of the vestibulocochlear nerve.

Answers to “Do You Know the Basics?”

1. B Feedback: Free nerve endings are unencapsulated tactile receptors.

2. D Feedback: Thermoreceptors detect changes in temperature.

3. B Feedback: The conjunctiva does not cover the surface of the cornea so no blood vessels will interfere with passage of light into the eye.

4. C Feedback: Lacrimal fluid cleanses and moistens the anterior surface of the eye and it helps prevent bacterial infection.

5. A Feedback: Eye tunics are arranged: retina (innermost), vascular (middle) and fibrous (outermost).

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6. D Feedback: The pupil constricts to decrease light rays passing through the edges of the lens.

7. B Feedback: The external acoustic meatus directs sound waves through the outer ear to the tympanic membrane.

8. C Feedback: The spiral organ within the cochlear duct contains hair cells that convert sound waves into nerve signals.

9. A Feedback: The macula is a sensory receptor within the vestibule of the ear that monitors position of the head.

10. A Feedback: Olfaction is the only sense that is not integrated within the thalamus.

11. Chemoreceptors detect chemicals dissolved in fluid (taste buds on the tongue). Thermoreceptors detect temperature changes (present in the skin and hypothalamus). Photoreceptors detect changes in light intensity (rods and cones present in the retina of the eye). Mechanoreceptors respond to distortion of the plasma membrane (bulbous corpuscles in the dermis of the skin). Nociceptors detect painful stimuli (receptors in the skin that detect chemical, heat or mechanical damage).

12. Visceral nociceptors detect internal body damage whereas somatic nociceptors detect chemical, heat or mechanical damage to the body surface or skeletal muscles. Referred pain occurs when sensory nerve signals from certain viscera are perceived as originating within skin and skeletal muscle. This may happen because numerous visceral and cutaneous sensory neurons conduct nerve signals on the same ascending tracts within the spinal cord.

Thus, the somatosensory cortex in the brain is unable to accurately determine the actual source of the stimulus thus it is incorrectly localized.

13. The gustatory pathway carries taste sensations. (1) Primary neurons extend from gustatory cells of the tongue through paired cranial nerves VII (facial) and IX (glossopharyngeal) and then synapse in the nucleus solitaries of the medulla oblongata. (2) Secondary neurons travel from the nucleus solitarius and synapse in the thalamus. (3) Tertiary neurons travel from the thalamus and terminate in the primary gustatory cortex in the insula of the cerebrum.

14. (1) Odorant molecules dissolve in mucus within the nasal cavity and then bind to olfactory hairs on the olfactory receptor cells (bipolar neurons). (2) The olfactory hairs contain membrane chemoreceptors; action potentials are generated when the olfactory receptor cells are stimulated. (3) Axons of olfactory receptor cells form bundles (fascicles) of the olfactory nerves and they project through foramina in the cribriform plate of the ethmoid bone to enter an olfactory bulb. (4) Paired olfactory bulbs are the terminal ends of olfactory tracts.

Axons of olfactory nerves synapse with both mitral cells and tufted cells (secondary neurons) within the olfactory bulbs to form spherical structures called olfactory glomeruli. (5) Axons bundles of the mitral and tufted cells form the paired olfactory tracts that project directly to the primary olfactory cortex.

15. The iris is the most anterior region of the vascular tunic. It has two layers of smooth muscle fibers, the sphincter pupillae and the dilator pupillae muscles. The action of these muscles adjusts the diameter of the pupil which regulates the amount of light entering the eye.

16. The lens is capable of accommodation involving stimulation of the ciliary muscles to view objects that are closer than 20 feet. When ciliary muscles contract, the tension on the suspensory ligaments relaxes, allowing the shape of the lens to become rounded to permit near vision. The immediate relaxation of tension applied to the suspensory ligaments supporting the lens permits the lens to flatten, thus allowing the view of distant objects.

17. A lacrimal apparatus is associated with each eye. It has a lacrimal gland to produce lacrimal fluid.

Lacrimal fluid contains water, sodium ions, antibodies, and an antibacterial enzyme called lysozyme. The

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fluid lubricates the anterior surface of the eye. The fluid is drained into lacrimal puncta that drain into a nasolacrimal duct and then into the nasal cavity. Aqueous humor is a transparent, watery fluid that circulates within the anterior cavity of the eye. It is continuously produced by the ciliary processes into the posterior chamber and then moves through the pupil to the anterior chamber. The circulation of aqueous humor provides nutrients and oxygen to both the avascular cornea (inner epithelium) and the lens. It moves from the posterior chamber through the pupil to the anterior chamber, where it is eventually resorbed via the scleral venous sinus.

18. The bony labyrinth consists of a series of chambers and spaces within the petrous portion of the temporal bone. The bony labyrinth houses membrane-lined, fluid-filled tubes called the membranous labyrinth.

19. Sound waves are collected by the auricle and enter the external acoustic meatus before striking the external surface of the tympanic membrane. Vibration of the tympanic membrane causes movement by the auditory ossicles in the middle ear. This movement results in the generation of pressure waves within the inner ear that travel through the perilymph in the scala vestibuli. Pressure waves in the scala vestibuli cause the vestibular membrane to vibrate, ultimately resulting in pressure wave formation in the endolymph of the cochlear duct. A region of the basilar membrane is displaced resulting in the distortion of spiral organ hair cells against the tectorial membrane, which generates an action potential. Remaining pressure waves are transferred to the scala tympani and are absorbed by the round window.

20. The maculae of the utricle and saccule detect the position of the head relative to gravity during static equilibrium and linear acceleration of the head. When a linear force is applied to the otolithic membrane, its position shifts and a force is applied to the stereocilia, distorting them. Bending of the stereocilia results in a change in the amount of neurotransmitter released from the hair cells, and a simultaneous change occurs in the stimulation of the sensory neurons of the vestibular branch of the vestibulocochlear nerve. The ampullae within the cristae ampullaris of the semicircular canals detect rotational acceleration. As the head accelerates, endolymph within the corresponding canal lags behind, putting pressure on the cupula. Bending of the cupula causes a deflection of stereocilia, which in turn results in a change in the amount of neurotransmitter released from the hair cells, and a simultaneous change occurs in the stimulation of the sensory neurons of the vestibular branch of the vestibulocochlear nerve.

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: The sensation of taste is complemented by and relies heavily on olfaction. Odorant molecules from the food modify the perception of its taste.

2. B Feedback: Dilation of pupils requires sympathetic stimulation from the autonomic nervous system.

(Accommodation of the lens is controlled by the parasympathetic division of the ANS (motor neurons within the oculomotor nerve)). Movement of the eye in the orbit (including abduction of the eye) is caused by contraction of extrinsic muscles of the eye, which are controlled by the somatic nervous system.

3. A Feedback: Hair cells responsible for transduction of high-frequency sounds are located close to the oval window.

4. D Feedback: Macular degeneration results from physical distortion of the macula lutea, affecting the fovea centralis.

5. B Feedback: Angina pectoris often presents as pain on the left side of the body. This is referred pain from the heart projecting to the dermatomes of the left side of the chest, shoulder, or arms.

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Answers to “Can You Synthesize What You’ve Learned?”

1. A middle ear infection (otitis media) can often present as an earache, a reddened and/or bulging tympanic membrane, and possible irritation of the pharynx. This situation is common in small children, whose auditory tubes are relatively short and are positioned in a more horizontal plane, allowing for infections to move from the pharynx into the middle ear.

2. Smoking can lead to decreased taste sensitivity. The cessation of smoking has allowed taste buds to function at a normal level. Cigarette smoke has an effect on size and sensitivity of taste buds.

3. Hyperopia, or farsightedness, results from an inability to focus light onto the retina, because the eyeball is too short. Corrective lenses placed in front of the eyes can adjust the focal plane for this condition. Convex lenses are used to correct hyperopia, bringing the focal plane anteriorly.

With increasing age, the lens becomes less resilient and less able to become spherical. Thus, even if the suspensory ligaments relax, the lens may not be able to spring out of the flattened position into the more spherical shape needed for near vision, and reading close-up words becomes difficult. This age-related change is called presbyopia. Convex lenses are used to correct for presbyopia. (The degree of curvature of the convex lenses is greater for presbyopia.)

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Chapter 17 Answers to “What Did You Learn?”

1. The endocrine system exercises control between two specific locations in the body through secretion of hormones into the blood that affect its target cells. The nervous system exercises control between two specific locations in the body by way of neurons which synapse with their target cells.

2. Maintaining the homeostasis of blood composition, specifically blood glucose levels, is affected during diabetes mellitus.

3. The pituitary, pineal, thyroid, parathyroid, and adrenal glands are major endocrine organs. The hypothalamus, skin, thymus, heart, liver, stomach, pancreas, small intestine, adipose connective tissue, kidney, and gonads (testes and ovaries) have other functions in addition to their endocrine function.

4. Stimulation of the adrenal cortex by adrenocorticotropic hormone (ACTH) is an example of (a) hormonal stimulation.

5. Reproductive hormones produced in the gonads, hormones from the adrenal cortex, and thyroid hormones (biogenic amines) are all lipid-soluble.

6. Differences in solubility (lipid-soluble vs. water-soluble) influence both (1) the transport of the hormone within the blood and (2) how the hormone interacts with its target cells.

7. Leukotrienes being released from a damaged cell to initiate cellular changes in neighboring cells is a form of paracrine secretion.

8. Lipid-soluble hormones do not readily dissolve within the aqueous environment of the blood; thus, their transport within the blood requires carrier molecules.

9. Carrier proteins also function to prolong the half-life of the hormones.

10. As the rate of hormone synthesis and release increases, the concentration of the hormone within the blood increases. In contrast, if synthesis and release of the hormone decreases, its concentration within the blood decreases.

11. Lipid-soluble hormone receptors are usually located within the cytosol or nucleus of a target cell. Lipid-soluble hormones bind to these intracellular receptors to form a hormone-receptor complex, which binds to a particular DNA sequence resulting in transcription of mRNA and ultimately the synthesis of a specific protein.

12. The activation of protein kinase enzymes results in the phosphorylation of other molecules which either activates or inactivates those molecules.

13. The number of receptor molecules available for hormone binding directly influences the degree of cellular response to that hormone. A cell may decrease its number of receptors (down-regulation) and thereby reduce its sensitivity to a hormone.

14. Synergistic interaction occurs when the activity of one hormone reinforces the activity of another hormone. The response is greater than by either hormone alone.

15. Axons from groups of neurons extend from the hypothalamus to the posterior pituitary (specifically the pars nervosa). The dendrites and cell bodies of these neurons are within the hypothalamus. Unmyelinated axons from these neurons extend through the infundibulum as the hypothalamo-hypophyseal tract (which includes synaptic knobs) within the posterior pituitary.

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16. Neurosecretory cells within the supraoptic nucleus of the hypothalamus primarily produce ADH. Following its synthesis, the ADH is packaged within secretory vesicles and transported by fast axonal transport through unmyelinated axons to the synaptic knobs within the posterior pituitary. ADH is released from the posterior pituitary when nerve signals from the supraoptic nucleus are sent from the hypothalamus along the hypothalamo-hypophyseal tract.

17. The six primary hormones released from the anterior pituitary are: 1) thyroid-stimulating hormone (TSH), 2) prolactin (PRL), 3) follicle-stimulating hormone (FSH), 4) luteinizing hormone (LH), 5) Adrenocorticotropic hormone (ACTH), and 6) Growth hormone (GH). The release of these hormones is controlled by releasing other hormones from the hypothalamus: these are 1] thyrotropin-releasing hormone (TRH) for TSH, 2] prolactinreleasing hormone (PRH) for PRL (note: prolactin-inhibiting hormone or PIH inhibits prolactin release), 3] Gonadotropin-releasing hormone (GnRH) for FSH and LH, 4] corticotropin-releasing hormone (CRH) for ACTH, and 5] growth hormone-releasing hormone (GRH) for GH. (Note: growth hormone-inhibiting hormone (GHIH) inhibits growth hormone release.)

18. Growth hormone-releasing hormone (GHRH) from the hypothalamus causes the release of growth hormone from the anterior pituitary. Growth hormone stimulates the release of insulin-like growth factor 1 and 2 (IGFs) from the liver. GH and both IGFs stimulate cell growth and cell division, particularly within the skeletal and muscular systems. The release of both GHRH and GH are regulated by negative feedback. In response to increased levels of GH or increased levels of IGF, the hypothalamus is stimulated to release GHIH, which inhibits the release of GH from the anterior pituitary. GH also directly inhibits its own release from the anterior pituitary.

19. GH and IGFs have overlapping functions and all body cells have receptors for them. Binding of the hormones activates second messengers within the target cells, altering enzymatic pathways to increase protein synthesis, mitosis, cell differentiation, or a combination of these. Bone and muscle tissue are particularly affected by these hormones. Hepatocytes are also stimulated by GH to increase both glycogenolysis and gluconeogenesis while at the same time glycogenesis is inhibited.

20. Thyrotropin-releasing hormone (TRH) is produced within the hypothalamus and released into the hypothalamo-hypophyseal portal system. TRH causes the release of thyroid-stimulating hormone (TSH) from the anterior pituitary gland. TSH binds to the surface of follicular cells within the thyroid gland, permitting the release of thyroid hormone into the blood. Thyroid hormone stimulates target cells (effectors).

21. Thyroid hormone acts on target cells to increase the body’s metabolic rate and alter the availability of nutrient molecules within the blood to support the higher metabolic rate. The increased metabolic rate is supported by increased release of stored fuel molecules and increased delivery of oxygen. Thyroid hormone increases amino acid uptake and protein synthesis, as well as increased glucose uptake in all cells. It stimulates the production of the sodium-potassium pumps in neurons. The action of these additional pumps generates heat.

There is also an increase in cellular respiration enzymes within mitochondria. Hepatocytes are stimulated to increase glycogenolysis and gluconeogenesis in the liver; lipolysis increases in adipose tissue.

22. In response to stress, corticotropin-releasing hormone (CRH) is released from the hypothalamus into the hypothalamo-hypophyseal portal system in response to stress. CRH causes the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary. ACTH stimulates the release of glucocorticoids (cortisol) from the zona fasciculata of the adrenal cortex. Cortisol stimulates target cells (effectors).

23. Cortisol stimulates the liver to engage in gluconeogenesis using noncarbohydrate molecules (e.g., amino acids, glycerol) to form glucose, adipocytes to engage in lipolysis (and decrease the enzymatic pathway of lipogenesis). Cortisol also stimulates the catabolism of proteins (except in hepatocytes).

24. The pancreas performs both exocrine and endocrine activities. Pancreatic acinar cells produce pancreatic juice as an exocrine secretion that empties into the gastrointestinal (GI) tract to facilitate digestion. Endocrine cell clusters, called pancreatic islets or Islets of Langerhans, secrete hormones, including insulin and glucagon.

25. The stimulus is humoral (the hormone is released in response to changes in blood levels of a substance other than a hormone). Changing blood levels of glucose is the stimulus for release of insulin and glucagon.

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26. The stimulus for the release of insulin is an increase in blood glucose. Beta cells in the pancreas are the receptors that detect increased blood glucose. Beta cells are the control center within the pancreas that release insulin. The effector response to insulin includes: uptake of glucose by most cells (especially liver tissue), increased lipogenesis and decreased lipolysis in adipose connective tissue, and increased uptake of amino acids (stimulates protein anabolism) in all cells, especially muscle.

27. Growth hormone, thyroid hormone, cortisol and glucagon all cause the release of glucose into the blood.

(Only insulin does not.)

28. Melatonin production tends to be cyclic; it increases at night, decreases during the day, and has the lowest levels around lunchtime.

29. The primary hormone released by the parathyroid gland is parathyroid hormone (PTH). Its general function is to increase blood calcium.

30. When chemoreceptors within the kidney detect low blood oxygen levels, endocrine tissue within the kidney releases erythropoietin (EPO). This hormone stimulates red bone marrow to increase the production rate of red blood cells.

31. The liver releases angiotensinogen. It is an inactive hormone that is activated while circulating within the blood. Its effects are meant to work together to keep blood pressure within normal homeostatic limits; these effects are: (1) it constricts blood vessels, (2) it stimulates the thirst center, and (3) it stimulates the kidney to decrease urine output.

32. Aging reduces the efficiency of endocrine system functions, and often levels of hormones decrease.

Answers to “Do You Know the Basics?”

1. D Feedback: The endocrine system does not control programmed cell death.

2. B Feedback: Thyroid hormone regulates the basal metabolic rate of the body.

3. D Feedback: G protein, cAMP, and protein kinases are all involved in second messenger systems.

4. B Feedback: Growth hormone is released from the anterior pituitary gland. Glucagon is released from the pancreas, melatonin from the pineal gland, and epinephrine from the adrenal medulla.

5. B Feedback: Lipid-soluble hormones bind with intracellular receptors to form hormone-receptor complex, which binds with hormone-responsive elements (components of the DNA).

6. C Feedback: Glycogenesis is the synthesis of glycogen from glucose obtained from the blood.

7. A Feedback: Glucagon has an antagonistic (opposite) effect compared to insulin on target cells.

8. D Feedback: Glucocorticoids regulate glucose levels in the blood.

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9. C Feedback: Thyroid-stimulating hormone binds to receptors on follicular cells within the thyroid gland, stimulating the release of thyroid hormone.

10. B Feedback: Antidiuretic hormone is produced in the hypothalamus, and released from the posterior pituitary.

11. The endocrine system targets all cells in the body that have a receptor for the specific hormone. It exercises control through secretion of hormones into the blood that affect its target cells. The nervous system exercises control between two specific locations in the body by way of neurons which synapse directly on its target cells where it releases neurotransmitters to stimulate the target cells. The nervous system targets specific neurons, muscles, or glands.

12. The endocrine system (1) regulates development, growth, and metabolism; (2) maintains homeostasis of blood composition and volume; (3) controls digestive processes; and (4) controls reproductive activities.

13. Hormone release may be stimulated: 1) by other hormones (hormonal), 2) in response to levels of molecules in the blood (humoral), or (3) through stimulation by the nervous system (nervous).

14. The three chemical classes of hormones and an example of each are: (1) steroid hormones (e.g., cortisol); (2) biogenic amines (e.g., norepinephrine); and (3) protein hormones (e.g., parathyroid hormone). Protein hormones are the most common.

15. Local hormones are signaling molecules that do not enter the blood. They bind with the same cell that produced them (autocrine stimulation) or neighboring cells (paracrine stimulation). Circulating hormones enter the blood and are transported through the body.

16. Lipid-soluble hormones are small, nonpolar molecules that do not readily dissolve within the aqueous environment of the blood. They are transported by carrier molecules. Lipid-soluble hormones diffuse across the plasma membrane, enter the cell, and bind to intracellular receptors located in either the cytosol or nucleus. The hormone-receptor complex that is formed then binds to a particular DNA sequence, resulting in transcription of messenger RNA. The translation of this mRNA synthesizes a specific protein.

17. Water-soluble hormones (polar molecules) cannot enter the cell. These hormones must bind to a receptor on the extracellular surface of the membrane, which will transduce the stimulus into the cell and result in the activation of a second messenger system. Formation of second and third messengers (e.g., cAMP, DAG, IP3, Ca2+) either alter protein kinase activity, change a cell’s permeability to ions, or both. Ultimately, the action may result in either activation or inhibition of enzymatic pathways, stimulation of growth through cellular division, release of cellular secretions, changes in membrane permeability, and muscle contraction or relaxation.

18. Axons from groups of neurons extend from the hypothalamus to the posterior pituitary. The dendrites and cell bodies of these neurons are within the hypothalamus. Unmyelinated axons from these neurons extend through the infundibulum as the hypothalamo-hypophyseal tract. The ends of these axons are located within the pars nervosa. The posterior pituitary stores hormones synthesized in the hypothalamus. The posterior pituitary is stimulated to release either antidiuretic hormone (ADH) or oxytocin in response to nerve signals initiated in the hypothalamus and conducted to the posterior pituitary along the hypothalamo-hypophyseal tract.

19. Hormones produced in the hypothalamus are transported through the hypothalamo-hypophyseal portal system to the anterior pituitary gland. Those hormones stimulate specific cells of the anterior pituitary to release their hormones into the general circulation.

20. Beta cells in the pancreas detect increased levels of blood glucose and respond by releasing insulin. Insulin stimulates target cells to decrease all nutrients (glucose, fatty acids, and amino acids) in the blood and an increase in the synthesis of the storage of these molecules within body tissues. (a) Glycogenesis in hepatocytes is stimulated and both glycogenolysis and gluconeogenesis are inhibited, resulting in glucose molecules being removed from the blood and stored as glycogen within liver cells. (b) Lipogenesis in adipose connective tissue cells is stimulated and lipolysis is inhibited. Fatty acid levels in the

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blood decrease and the storage of fat is increased as a result. (c) Most cells are stimulated to increase their cellular uptake of (1) amino acids (especially muscle cells), a change that induces cells to increase protein anabolism (synthesis of amino acids into protein), and (2) glucose, especially by the cells of muscle and adipose connective tissue.

By decreasing alternative nutrients (fatty acids and amino acids), the cells of the body are more likely to use the available glucose and help return blood glucose to a normal level more quickly. The release of insulin is controlled by negative feedback; as blood glucose levels decrease, less insulin is released from the pancreas.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: Hyperthyroidism can result in an enlarged thyroid gland. Increased thyroid hormone levels can cause weight loss and hyperactivity.

2. A Feedback: The thyroid gland incorporates iodine from the blood into the thyroid hormone.

3. B Feedback: Epinephrine and cortisol are released in response to stress. Epinephrine prolongs the effects of the sympathetic nervous system, and cortisol increases the uptake and availability of nutrients.

4. C Feedback: Insulin is released in response to increased blood glucose, and causes the uptake of glucose by tissues.

Thus, insufficient insulin results in less glucose uptake by tissues with more glucose remaining in the blood.

5. D Feedback: Cortisol stimulates gluconeogenesis in the liver, and lipolysis in adipocytes. It also causes protein catabolism and release of amino acids from all other tissues.

Answers to “Can You Synthesize What You’ve Learned?”

1. Type I diabetes results in diminished insulin release from beta cells of the pancreas. Insulin is required to stimulate cells of the body to take up glucose, thereby lowering blood glucose levels. Elevated blood glucose levels suggest that adequate levels of insulin are not being produced.

2. The posterior pituitary gland releases oxytocin and antidiuretic hormone. The anterior pituitary releases the trophic hormones: thyroid-stimulating hormone, adrenocorticotropic hormone, growth hormone, luteinizing hormone, follicle-stimulating hormone, and prolactin. All of the processes regulated by these hormones would be affected.

3. Thyrotropin-releasing hormone (TRH) is produced within the hypothalamus and released into the hypothalamohypophyseal portal system. TRH causes the release of thyroid-stimulating hormone (TSH) from the anterior pituitary gland. TSH binds to the surface of follicular cells within the thyroid gland, permitting the release of thyroid hormone into the blood. Thyroid hormone inhibits the further release of TRH and TSH, providing for negative feedback.

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Chapter 18 Answers to “What Did You Learn?”

1. Blood transports formed elements such as erythrocytes, leukocytes, and platelets, and dissolved molecules and ions throughout the body.

2. Blood helps regulate body temperature by absorbing heat from body cells, especially muscle, as it passes through vessels in body tissues. Heat is released from the blood at the body surface as it passes through vessels in the skin. Blood also helps maintain fluid balance as water is added to it from the gastrointestinal tract to replace the fluid lost in urine, sweat and respired air. A constant exchange of fluid occurs between blood plasma in capillaries and interstitial fluid surrounding cells in body tissues.

3. If the pH of blood is altered from the normal range, plasma proteins become denatured and are unable to carry out their functions.

4. The three components of blood visible in a centrifuged blood sample (from bottom to top) are the erythrocytes, buffy coat, and plasma.

5. Hematocrit values vary somewhat and are dependent upon the age and sex of the individual. Adult males tend to have a hematocrit ranging between 42% and 56%, whereas adult females’ hematocrits range from 38% to 46%. An increased hematocrit may be an indicator that the patient is suffering from dehydration.

6. Plasma proteins exert osmotic pressure and prevent the loss of fluid from the blood as it moves through the capillaries. Osmotic pressure exerted by plasma proteins is called colloid osmotic pressure. This osmotic force is responsible for drawing fluids into the blood and preventing excess fluid loss between blood capillaries and the interstitial fluid, thus maintaining blood volume and pressure.

7. Albumins are the most abundant of the plasma proteins. Therefore they exert the greatest colloid osmotic pressure to maintain blood volume and blood pressure. Also, they serve as transport proteins for ions, hormones, and some lipids in the blood.

8. The main dissolved substances in plasma include electrolytes, nutrients, gases, and waste products.

9. Erythropoiesis begins with a 1) myeloid stem cell, which forms a 2) progenitor cell (under the influence of multi-CSF). The progenitor cell forms a 3) proerythroblast (a large, nucleated cell), that becomes an 4) erythroblast (a slightly smaller cell producing hemoglobin in its cytosol). The next stage is a 5) normoblast (a still smaller cell that has more hemoglobin in the cytosol; also, its nucleus has been ejected). Eventually a 6) reticulocyte is formed - it has lost all organelles except some ribosomes as it continues to produce hemoglobin.

One to two days after entering the circulation, the organelles in the reticulocyte degenerate. The 7) erythrocyte has been produced.

10. Hemocytoblasts give rise to two different lines for blood cell development: 1) the myeloid line that forms erythrocytes, all leukocytes except lymphocytes (this means that they form granulocytes and monocytes), and megakaryocytes (cells that produce platelets), and 2) the lymphoid line (cells that produce only lymphocytes).

11. The main function of an erythrocyte is to transport oxygen and carbon dioxide between the tissues and the lungs. They are designed to carry out this function efficiently by 1) being small and flexible, and having a biconcave disc shape (and thus they stack to pass through the smallest blood vessels) and 2) lacking a nucleus and organelles, and being filled with hemoglobin molecules (optimized to more efficiently transport respiratory gases).

12. The iron component in hemoglobin is removed and then transported by the globulin protein called transferrin to the liver where the iron is bound to the storage protein called ferritin.

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13. Type A+ blood has both the surface antigen A (type A) and the surface antigen D (type Rh+) on the surface of erythrocytes. Type B- has only the surface antigen B (type B) on the surface of erythrocytes.

14. Neutrophils are the granulocyte that will increase in response to a bacterial infection that would cause strep throat.

15. The person is healthy in terms of the white blood cell differential count. The normal range for leukocytes in the blood is 4,500 to 11,000 circulating cells per microliter, where 50-70% of the cells are neutrophils.

16. Platelets serve an important function in hemostasis (blood clotting). They circulate in the blood for 8 to 10 days.

17. During a vascular spasm a blood vessel constricts suddenly and, in so doing, limits the amount of blood that can leak from the damaged vessel. The vascular spasm phase usually lasts from a few to many minutes.

18. Prostacyclin on the endothelial wall (inner surface lining of a blood vessel) activates a pathway in both platelets and endothelial cells that involves production of cAMP to ultimately inhibit platelet activation. Thus, prostacyclin serves as a platelet repellent.

19. Platelets serve a central function in all three phases of hemostasis: 1) Vascular spasm - platelets release serotonin and thromboxane A2 to prolong vascular spasms; 2) Platelet plug formation - damage to a vessel wall results in platelets sticking to exposed collagen fibers, changing their morphology, and then they aggregate and form a ‘plug’ to temporarily block the flow of blood; 3) Coagulation - a clot formation in which platelets become part of the meshwork to form the clot.

20. The intrinsic pathway is initiated by damage to the inside of the vessel wall and is initiated by platelets. This pathway typically takes approximately 3 to 6 minutes. In contrast, the extrinsic pathway is initiated by damage to the tissue that is outside of the vessel, and this pathway usually takes approximately 15 seconds.

21. The sympathetic division of the autonomic nervous system is activated when over 10% of the blood volume is lost from blood vessels. It is termed a survival response. As blood volume decreases, blood pressure decreases. Activation of the sympathetic division of the ANS causes vasoconstriction, increased heart rate, and increased force of heart contraction in an attempt to maintain blood pressure.

22. Fibrinolysis is the degradation of fibrin strands in a clot by plasmin, resulting in the destruction of the fibrin framework of the clot. Thus, fibrinolysis helps break down a clot when it is no longer needed.

23. Hemopoiesis occurs a) in the liver, spleen, and thymus of a fetus, b) in most bones in young children, and c) in selected bones within the axial skeleton in adults.

24. Most red bone marrow is replaced with fat in the elderly, so older individuals have relatively less bone marrow.

In addition, this older bone marrow may be less able to meet the demands of increased numbers of any type of formed elements.

Answers to “Do You Know the Basics?”

1. B Feedback: A male adult usually has a higher hematocrit because testosterone stimulates production of EPO, which promotes erythrocyte production. In addition, dehydration results in a higher hematocrit.

2. B Feedback: Eosinophils phagocytize antigen-antibody complexes and allergens, and also release chemical mediators to destroy parasitic worms.

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3. B Feedback: Platelets are derived from megakaryocytes.

4. D Feedback: Hormones are produced by glands and tissues that have endocrine function. Endocrine hormones are transported by the blood, but are not produced in blood.

5. A Feedback: A person with type A blood has erythrocytes with surface antigen A, and therefore has anti-B antibodies in the blood plasma.

6. B Feedback: The hematocrit corresponds to the percentage of whole blood that is composed of all formed elements.

7. C Feedback: Oxygen binds to iron ions in heme groups within hemoglobin for transport in the blood.

8. A Feedback: Globin proteins are broken down into free amino acids, which may then be used to produce new proteins.

9. D Feedback: The extrinsic pathway is initiated by damage to the tissue that is outside of the vessel, whereas the intrinsic pathway is initiated by damage to the inside of the vessel wall.

10. B Feedback: A clot has an insoluble network of fibrin that traps formed elements and platelets.

11. Blood absorbs heat from body cells and then releases the heat at the body surface as it is transported through vessels in the skin.

12. Alpha- and beta-globulins are plasma proteins. The smaller alpha-globulins and the larger beta-globulins primarily bind and transport certain water-insoluble molecules and hormones, some metals, and ions. Gammaglobulins are also called immunoglobulins, or antibodies, and they play a part in the body’s defenses.

13. The buffy coat contains leukocytes and platelets.

14. Erythrocytes have a unique biconcave disk structure that allows respiratory gases to be loaded and unloaded rapidly and efficiently. Additionally, their structure facilitates both a single-line stacking of these cells (termed a rouleau) as they pass through small blood vessels, and some flexibility of the cells to permit their passage through the smallest vessels.

15. Oxygen is transported through the blood as oxyhemoglobin bound to the iron-containing heme groups of hemoglobin. Carbon dioxide binds to the globin protein molecule as blood moves through systemic capillaries and is released as blood moves through the capillaries of the lung.

16. Neutrophils have a multilobed nucleus (as many as five lobes) and cytosol with pale-colored granules.

Eosinophils have a bilobed nucleus and cytosol with pink-orange to reddish granules. Basophils have a bilobed nucleus and cytosol with deep-purple granules. Lymphocytes have a round nucleus that fills the cell; the nucleus is darkly stained and surrounded by a thin rim of cytosol. These four leukocytes are about one and a half times the diameter of an erythrocyte. Monocytes have a kidney-bean shaped or C-shaped pale-staining nucleus with abundant cytosol. They are almost three times the diameter of an erythrocyte.

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17. Basophils are involved in the release of histamine and heparin during anti-inflammatory or allergic reactions. Lymphocytes attack pathogens, destroy cancer cells, coordinate immune cell activity and produce antibodies.

18. Platelets are cell fragments continually produced in the red bone marrow by cells called megakaryocytes.

They help produce clots to prevent blood loss.

19. Lymphocytes are derived from a precursor cell called a lymphoid stem cell. Granulocytes and monocytes are derived from a precursor cell called a myeloid stem cell. The precursor cells in the lymphoid line are Blymphoblasts (that form B-lymphocytes) and T-lymphoblasts (that form T-lymphocytes). Natural killer cells are derived directly from the lymphoid stem cell. Granulocytes and monocytes are further derived from a progenitor cell that gives rise to a granulocyte line; this line forms a myeloblast that yields promyelocytes, which then form the specific granulocytes that are eosinophils, basophils, and neutrophils. The common cell from which all leukocytes originate is the hemocytoblast.

20. The three phases of hemostasis are vascular spasm, platelet plug formation, and coagulation. The vascular spasm involves constriction of the damaged blood vessel, limiting blood loss. Platelet plug formation begins with adhesion of platelets to exposed collagen fibers at the site of the damage, forming the initial plug in the vessel wall. The subsequent coagulation phase is characterized by the production of an insoluble fibrin mesh, formed from plasma fibrinogen and numerous formed elements within the blood and ultimately yielding a blood clot.

Answers to “Can You Apply What You’ve Learned?”

1. D Feedback: Taylor cannot receive blood containing the B antigen or the Rh D (Rh+ ) antigen. O- blood does not contain any antigens; it is the universal donor blood type.

2. A Feedback: Ibuprofen, if taken in high enough doses, can interfere with blood coagulation.

3. C Feedback: Trauma leading to the rupture of vessels will trigger the extrinsic hemostatic pathway, which will initiate the common pathway, and finally clotting.

4. C Feedback: Neutrophils defend against bacterial infections. A high neutrophil count, accompanied by a fever, would indicate a bacterial infection.

5. B Feedback: Because Taylor is Rh- and her baby is Rh+, once she was exposed to her baby’s anti-D antibodies, her body would attack any subsequent conception that was Rh+.

Answers to “Can You Synthesize What You’ve Learned?”

1. Eosinophils are granulated and readily take up eosin, a stain that makes them a pinkish-orange color.

Normally, eosinophils are found within 1–4% of a differential blood count. Increased levels of eosinophils in the blood may indicate an allergic reaction, or a parasitic infection.

2. The patient would be given O- blood. O- blood does not contain any antigens of the ABO blood group nor the Rh D antigen. It is therefore the universal donor blood type. It has no surface antigens to trigger agglutination in a recipient, regardless of blood type.

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3. An athlete involved in blood doping is trying to get a competitive advantage by artificially increasing the number of red blood cells available to the body and thereby improving cardiovascular function. This can be accomplished in one of two ways: 1) an athlete can remove a volume of his own blood, forcing his body to produce new blood cells, and then reintroduce the original blood back into his body, thereby increasing the number of red blood cells, or 2) another option is to inject EPO, a synthetic hormone that stimulates red blood cell production. However, there is an inherent danger in increasing the number of formed elements in the blood and thereby increasing its viscosity. This increases total peripheral resistance that may result in blood vessels forcing the heart to work harder.

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Chapter 19 Answers to “What Did You Learn?”

1. A failing cardiovascular system will result in tissues that are deprived of needed oxygen and nutrients, waste product accumulation, and possible cell death.

2. All arteries carry blood away from the heart. All veins carry blood toward the heart.

3. Deoxygenated blood returning from the systemic circulation 1) enters the right atrium from the superior vena cava, the inferior vena cava, and the coronary sinus. This blood is now in the pulmonary circulation. It flows through the 2) right atrioventricular valve into the 3) right ventricle. The blood then passes through the 4) pulmonary semilunar valve and enters into the 5) pulmonary trunk and then into the 6) pulmonary arteries that go to both lungs. In the lungs the blood enters the 7) pulmonary capillaries for gas exchange. This blood is now oxygenated and returns to the heart through the 8) right and left pulmonary veins. This oxygenated blood enters the 9) left atrium and is now in the systemic circulation. It then passes through the 10) left atrioventricular valve into the 11) left ventricle. The blood then passes through the 12) aortic semilunar valve and enters the 13) aorta.

Blood is then distributed throughout the body by the 14) systemic arteries and eventually enters the 15) systemic capillaries. Deoxygenated blood leaves the systemic capillaries and ultimately drains into the 16) superior vena cava, inferior vena cava, and coronary sinus before re-entering the right atrium.

4. The great vessel that is both an artery and transports deoxygenated blood is the pulmonary trunk. The great vessels that are both veins and transport oxygenated blood are the pulmonary veins.

5. The position of the heart is slightly rotated such that its right side or border (right atrium and ventricle) is located more anteriorly, while its left side or border (left atrium and ventricle) is located more posteriorly.

6. The pericardium is composed of three layers: 1) an outer fibrous pericardium (tough, dense irregular connective tissue enclosing the heart but not attached to it; rather, it is attached inferiorly to the diaphragm and superiorly to the base of the great arterial trunks); 2) the parietal layer of the serous pericardium (a simple squamous epithelium and an underlying delicate layer of areolar connective tissue) that adheres to the inner surface of the fibrous pericardium; and 3) the visceral layer of the serous pericardium (composed of a simple squamous epithelium and an underlying delicate layer of areolar connective tissue) that directly adheres directly to the heart. (Note that the serous pericardium is also called the epicardium.)

7. The coronary sulcus (or atrioventricular sulcus) is a relatively deep groove around the circumference of the heart located between the atria and ventricles. This groove houses coronary blood vessels. One of the coronary vessels within the coronary sulcus is the coronary sinus, which is visible only on the posterior aspect of the heart.

8. The scalpel would pass through (in order): 1) the epicardium, 2) the myocardium, and 3) the endocardium.

The two names of the outer layer of the heart wall are a) epicardium and b) visceral layer of serous pericardium.

9. The interventricular septum separates the left and right ventricles. The position of the interventricular septum is identified by the superficial landmark on the heart’s ventral surface called the anterior interventricular sulcus.

10. The tendinous cords (or chordae tendineae) are thin strands of collagen fibers that extend between the papillary muscles and the cusps of the atrioventricular valves. They function to prevent the valve from prolapsing (inverting and flipping into the atrium) when the ventricle is contracting. Thus, blood flow back into the atrium from the ventricle is prevented.

11. Cardiac muscle has features that support its great demand for energy. These include: 1) an extensive blood supply, 2) numerous mitochondria, and 3) structures such as myoglobin and creatine kinase. Cardiac muscle relies almost exclusively on aerobic cellular respiration. In addition, cardiac muscle has versatility in being able

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to use many different types of molecules as fuel for aerobic respiration, including fatty acids, glucose, lactate, amino acids, and ketone bodies.

12. The fibrous skeleton of the heart acts as an electric insulator because it does not conduct action potentials and thus allows the atria to contract separately from the ventricles.

13. The posterior interventricular artery provides blood to the posterior surfaces of the right and left ventricles.

Blockage of the posterior interventricular artery would deprive these regions of blood.

14. The coronary sinus receives deoxygenated blood from the myocardium that has drained into several cardiac veins (the great cardiac vein, middle cardiac vein, and small cardiac vein). It then returns this deoxygenated blood directly into the right atrium of the heart.

15. The cells of the sinoatrial node initiate the heartbeat, and are therefore commonly referred to as the “pacemaker” of the heart.

16. The cardioacceleratory center is the origin of sympathetic innervation for the heart. Stimulation by the sympathetic division increases both heart rate and the force of heart contraction. There is also some sympathetic innervation to the coronary arteries, causing dilation of these vessels to support increased blood flow to the myocardium.

17. Nodal cells have a resting membrane potential of –60 mV. 18. Autorhythmicity refers to the ability of the SA nodal cells to depolarize and generate an action potential spontaneously without any external influence. This process involves three steps. 1) Reaching threshold: an initial influx of Na+ into the cell through slow voltage-gated Na+ channels that open in response to repolarization from the previous action potential. The cell membrane potential changes from –60 mV to its threshold of –40mV. 2) Depolarization: changing of membrane potential triggers the opening of fast voltage-gated Ca2+ channels. This allows Ca2+ entry into the nodal cell, causing a change in membrane potential from -40 mV to a slightly positive membrane potential (just above 0 mV). This reversal in polarity is the depolarization. 3) Repolarization: calcium channels close and voltage-gated K+ channels open, allowing K+ to flow out to change the membrane potential from a positive value (just above 0 mV) to -60 mV (the resting membrane potential) and once again triggering the opening of slow voltage-gated Na+ channels.

19. 1) The action potential is generated in the sinoatrial node and spreads via gap junctions between cardiac muscle cells throughout the atria to the atrioventricular (AV) node. 2) The action potential is delayed at the AV node before it passes to the AV bundle within the interventricular septum. 3) The AV bundle conducts the action potential along the left and right bundle branches to the Purkinje fibers in the ventricles. 4) The action potential is spread via gap junctions between cardiac muscle cells throughout the ventricles.

20. AV nodal cells have both smaller fiber diameters and fewer numbers of gap junctions, and thus they exhibit characteristics that slow the conduction rate of the action potential. This is facilitated by the insulating characteristics of the fibrous skeleton, which only allow the action potential to move through the AV node. The delay is “brief,” but it is long enough to allow the atria to finish contracting and force blood into the ventricles to complete ventricular filling before the ventricles are stimulated to contract.

21. Slow voltage-gated Ca2+ channels within the sarcolemma allow calcium to enter cardiac muscle cells.

22. 1) Depolarization: fast voltage-gated Na+ channels open and Na+ rapidly enters the cell, reversing the polarity from negative to positive (-90 mV to +30 mV). 2) Plateau: voltage-gated K+ channels open and K+ flows out of cardiac muscle cells. Slow voltage-gated Ca2+ channels open and Ca2+ enters the cell. This results in no electrical change in the membrane potential and the depolarized state is maintained. (3) Repolarization: voltage-gated Ca2+ channels close while voltage-gated K+ channels remain open; K+ moves out of the cardiac muscle cell and polarity is reversed from positive to negative (+30 mV to -90 mV).

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23. The plateau phase of cardiac muscle cell contraction allows for a prolonged refractory period which delays repolarization. There is an extended period of time in which the cardiac muscle cell cannot be re-stimulated, allowing the cardiac muscle to both contract and relax before it is stimulated again. This prevents cardiac muscle cells from developing a sustained contraction (or tetany).

24. The P wave reflects electrical changes of atrial depolarization that originates in the SA node. The QRS complex represents the electrical changes associated with ventricular depolarization. (Note that the atria are simultaneously repolarizing; however, this repolarization signal is masked by the greater electrical activity of the ventricles.) The T wave is the electrical change associated with ventricular repolarization.

The two segments between the waves correspond with the plateau (where there is essentially no electrical change in the membrane potential at the sarcolemma). During these time periods, the sarcomeres are shortening within the cardiac muscle cells. The P-Q segment is associated with the atrial plateau at the sarcolemma when the cardiac muscle cells within the atria are contracting, and the S-T segment is the ventricular plateau when the cardiac muscle cells within ventricles are contracting.

25. Pressure changes that occur during the cardiac cycle produce 1) the unidirectional movement of blood through the heart chambers as blood moves along a pressure gradient from an area of greater to an area of lesser pressure and 2) the opening and closing of heart valves to ensure that blood continues to move in a “forward” direction without backflow.

26. Ventricular ejection occurs as the semilunar valves are forced open and blood moves from the ventricles into the arterial trunks (the pulmonary trunk and the aorta).

27. Ventricular contraction causes both the AV valves to close and then the semilunar valves to open. Ventricular contraction results in an increase in ventricular pressure during isovolumetric contraction; this rise in pressure first closes the AV valve and then opens the semilunar valves (which results in ventricular ejection).

28. The end-diastolic volume (EDV) is the amount of blood that a relaxed ventricle contains after atrial contraction. The end-systolic volume (ESV) is the amount of blood remaining in a ventricle at the end of contraction. The amount of blood pumped out of the ventricle during ventricular contraction is termed the stroke volume (SV). ESV is determined by subtracting SV from EDV (EDV – SV = ESV): 130 mL – 70 mL = 60 mL. 29. Cardiac output is the amount of blood that is pumped by one ventricle in one minute. It is typically expressed as liters per minute. It is determined by the product of heart rate (number of beats per minute) times stroke volume (volume of blood ejected during one beat).

30. The resting cardiac output would be (75 beats/min × 70 mL/beat) = 5.25 L/min. The cardiac output during exercise would be (150 beats/min × 100 mL/beat) = 15.0 L/min. The cardiac reserve is the increase in cardiac output above its level at rest. In the example given here, the cardiac reserve would be 9.75 L/min: 15.0 L/min – 5.25 L/min = 9.75 L/min.

31. A positive chronotropic agent increases heart rate. Examples of positive chronotropic agents include: norepinephrine released from sympathetic axons and epinephrine and norepinephrine from the adrenal medulla (which stimulate opening of Ca2+ channels, allowing additional entry of Ca2+ into nodal cells), nicotine (which increases release of norepinephrine from sympathetic axons), cocaine (which decreases reuptake of norepinephrine so that it remains in the synaptic cleft longer), and caffeine (which inhibits breakdown of cAMP so that calcium channels remain open). A negative chronotropic agent decreases heart rate. Examples of negative chronotropic agents include acetylcholine released from parasympathetic axons (which stimulates opening of K+ channels, allowing efflux of K+ that hyperpolarizes the nodal cells. Also, drugs that block the receptors (β1receptors) for norepinephrine; these drugs are called β-blockers.

32. The atrial reflex, also called the Bainbridge reflex, protects the heart from overfilling. It is initiated when baroreceptors (stretch receptors) in the atrial walls are stimulated by an increase in venous return. Nerve signals are increased along sensory neurons to the cardioacceleratory center, resulting in an increase in nerve signals relayed through sympathetic axons to the heart. Heart rate increases so blood moves more quickly through the heart, thus decreasing atrial stretch.

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33. Increased venous return causes stretching of the heart walls, causing an increased preload, which increases the force of the subsequent contraction, and therefore increases stroke volume. (Increased calcium in the sarcoplasm increases the number of Ca2+ ions available to bind to troponin, also increasing the force of contraction. Afterload is the resistance in arteries to the ejection of blood by the ventricles. As arteries become narrower in diameter, there is an increase in the resistance to pump blood into the arteries and stroke volume decreases.)

34. Stroke volume and heart rate have a direct relationship; therefore, as both variables increase, so does cardiac output.

35. Deoxygenated blood from the end of the systemic circuit would enter the right atrium and flow directly into the left atrium through the foramen ovale. It then would move into the left ventricle and would again enter into the systemic circuit, thus bypassing the pulmonary circuit and it would not be re-oxygenated.

Answers to “Do You Know the Basics?”

1. B Feedback: Blood returning from the systemic circuit enters the right atrium from the superior vena cava, inferior vena cava, and the coronary sinus. It flows through the right atrioventricular valve into the right ventricle and then through the pulmonary semilunar valve into the pulmonary trunk.

2. B Feedback: The serosal pericardium is composed of two layers: a parietal layer that adheres to the inner surface of the fibrous pericardium and a visceral layer that adheres directly to the heart. The space between the parietal and visceral layers is the pericardial cavity.

3. D Feedback: The pulmonary semilunar valves prevent the backflow of blood from the pulmonary trunk back into the right ventricle.

4. A Feedback: Blood returning from the heart wall drains to the right atrium through the coronary sinus.

5. A Feedback: Calcium channels allow an influx of calcium ions into a nodal cell, causing depolarization as the membrane potential of the nodal cells is changed from -40 mV to just above 0 mV. 6. B Feedback: Gap junctions within intercalated discs between cardiac muscle cells allow calcium to flow across to adjacent cardiac muscle cells, thereby allowing propagation of the action potential from cell to cell.

7. B Feedback: Contraction of the papillary muscles puts tension on the AV valve flaps through the tendinous cords, thereby preventing prolapse of the valves and the subsequent backflow of blood into the atria.

8. A Feedback: Preload is a measure of stretch of the heart wall due to the amount of blood that enters the chamber just before it contracts.

9. D Feedback: Blood from the pulmonary trunk is transported to the lungs through the pulmonary arteries.

Pulmonary veins then bring blood back to the left atrium.

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10. D Feedback: During the atrial reflex, increased venous return to the atria stimulates baroreceptors within the atria that initiate an increase in nerve signals to the cardiac center. In response, increased nerve signals are relayed from the cardioacceleratory center to the heart, which increases both the heart rate and force of contraction.

11. The pulmonary circuit carries deoxygenated blood from the right ventricle to the lungs through pulmonary arteries and then oxygenated blood through pulmonary veins back to the left atrium. The systemic circuit carries oxygenated blood from the left ventricle through systemic arteries to all regions of the body, and then deoxygenated blood back to the left atrium through systemic veins.

12. The parietal layer of serous pericardium is a serous membrane (simple squamous epithelium with underlying areolar connective tissue) that adheres to the inner surface of the fibrous pericardium, which is itself composed of dense irregular connective tissue and encloses the heart but does not attach to it. The visceral layer of serous pericardium (also called the epicardium) is a serous membrane (simple squamous epithelium with underlying areolar connective tissue) that adheres directly to the heart. Together, both layers produce serous fluid in the pericardial cavity to reduce friction as the heart moves during beating.

13. Tendinous cords are thin strands of collagen fibers that anchor into papillary muscles and attach to the cusp of the atrioventricular valves to prevent these valves from prolapsing (inverting and flipping into the atrium) when the ventricle is contracting.

14. The atria are thin walled because they do not need to generate high pressure to push blood into the ventricles.

Most of the filling of the ventricles is passive, and the ventricles are inferior to the atria so moving blood into the ventricles from the atria is assisted by gravity. The right ventricle wall is relatively thin with respect to the left ventricle wall because the right ventricle only has to pump blood through the pulmonary circuit to the adjacent lungs immediately lateral to the heart, whereas the left ventricle must generate enough pressure to drive blood through the entire systemic circuit.

15. Intercalated discs are found at cell-to-cell junctions that attach adjacent cardiac muscle cells and link them together both mechanically and electrically. They have two distinctive structural features: 1) desmosomes, which are protein structures that act as mechanical junctions to prevent cardiac muscle cells from pulling apart, and 2) numerous gap junctions (protein pores) between adjacent cardiac muscle cells that provide a pathway for ion flow between cardiac muscle cells, which allows an action potential to move continuously along the sarcolemma of adjacent cells, resulting in synchronous contraction of the heart chamber.

16. The right and left coronary arteries are positioned within the coronary sulcus of the heart to supply the heart wall. Branches of these coronary arteries supply specific regions of the heart (example: anterior and posterior interventricular arteries within sulci between the ventricles). Coronary vessels transport oxygenated blood to the wall of the heart (coronary arteries) and deoxygenated blood away from the heart wall (coronary veins). The coronary sinus transports deoxygenated blood from the myocardium back to the right atrium.

17. Parasympathetic innervation comes from the cardioinhibitory center within the cardiac center in the medulla oblongata. It decreases heart rate, but generally has no direct effect on the force of contraction. Sympathetic innervation comes from the cardioacceleratory center within the cardiac center in the medulla oblongata. It increases heart rate and increases the force of the heart contractions.

18. Conduction system: Spontaneous depolarization of cells within the sinoatrial node initiates an action potential that is propagated through gap junction across the cells of the left and right atria, causing atrial systole.

As the atria are contracting, the action potential stimulates the atrioventricular node at the base of the right atrium. From here it travels along the AV bundle and the bundle branches within the interventricular septum, and finally to the Purkinje fibers. The slow conduction through the AV node ensures that the signal does not reach the ventricles until atrial diastole, at which point the Purkinje fibers generate an action potential within the myocardium of the ventricles, causing ventricular systole.

Cardiac muscle cells: Three electrical events occur at the sarcolemma of cardiac muscle cells that include 1) depolarization, which is due to the opening of fast voltage-gated Na+ channels that allows rapid entry of Na+ into the cell that reverses the polarity from negative to positive (-90 mV to +30 mV), 2) plateau, which is due to a) the opening of voltage-gated K+ channels that allows outflow of K+ and b) the opening of slow voltage-gated Ca2+

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channels that allows inflow of Ca2+, resulting in no electrical change (depolarized state is maintained); and 3) repolarization, which is due to the closing of voltage-gated Ca2+ channels while voltage-gated K+ channels remain open, and this allows continued outflow of K+ to reverse polarity from positive to negative (+30 mV to -90 mV).

The entry of Ca2+ into the sarcoplasm from both the interstitial fluid and SR initiates the internal mechanical events of muscle contraction. Calcium ions now bind to troponin to begin crossbridge cycling within a sarcomere, similar to the way in which skeletal muscle contracts.

19. The events of the cardiac cycle, including contraction or relaxation of chambers and whether valves are open or closed, are: 1. Atrial Contraction and Ventricular Filling: Atria contract / Ventricles relax, AV valves open / Semilunar valves closed 2. Isovolumetric Contraction: Atria relax / Ventricles contract, AV valves closed / Semilunar valves closed 3. Ventricular Ejection: Atria relax / Ventricles contract, AV valves closed / Semilunar valves open 4. Isovolumetric Relaxation: Atria relax / Ventricles relax, AV valves closed / Semilunar valves closed 5. Atrial Relaxation and Ventricular Filling: Atria relax / Ventricles relax, AV valves open / Semilunar valves closed 20. Cardiac output is the amount of blood ejected from the heart in 1 minute. It is a function of the number of times that the heart contracts per minute (heart rate) and the amount of blood ejected with each contraction (stroke volume). Thus, CO = HR x SV.

Answers to “Can You Apply What You’ve Learned?”

1. D Feedback: When the heart contracts, the coronary arteries are compressed temporarily impeding blood flow to the heart wall. During tachycardia the amount of times the coronary arteries is compressed is increased.

2. B Feedback: Blood pressure monitoring would give an indication of the state of the circulatory system, which although influenced by the heart, is not a good indicator of heart health.

3. C Feedback: Calcium channel blockers cause a negative ionotropic effect, decreasing the contractility of the heart and subsequently decreasing cardiac output.

4. D Feedback: Decreased blood volume will cause decreased end-diastolic volume. Low end-diastolic volume will result in decreased stroke volume, and subsequent decreased cardiac output. The body will try to maintain cardiac output by increasing the heart rate.

5. B Feedback: Severing the vagus nerve will result in loss of vagal tone, allowing the SA node to increase the rate of contraction to either its own inherent pace or the pace set by any sympathetic stimulation.

Answers to “Can You Synthesize What You’ve Learned?”

1. Under normal conditions, in a fully developed heart, deoxygenated blood returning from the systemic circulation enters the right atrium from the superior vena cava, the inferior vena cava, and the coronary sinus. This blood is now in the pulmonary circulation. It flows through the right atrioventricular valve into the right ventricle.

The blood then passes through the pulmonary semilunar valve and enters into the pulmonary trunk. The deoxygenated blood is pumped to the lungs where it is reoxygenated. It then returns to the heart through the right and left pulmonary veins. This oxygenated blood enters the left atrium and is now in the systemic circulation. It

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then passes through the left atrioventricular valve into the left ventricle. The blood then passes through the aortic semilunar valve and enters the aorta to be distributed throughout the body.

The structural problem with the baby’s heart (open foramen ovale) means that deoxygenated blood returning to the right atrium immediately passes into the left atrium and mixes with oxygenated blood returning from the lungs to the left atrium. The foramen ovale must be surgically repaired to maintain the separation of deoxygenated and oxygenated blood through the heart.

2. Angina pectoris results from diminished blood supply to the myocardium, usually caused by occlusion of blood flow through coronary arteries. It presents as pain on the left side of the body, usually the arm, jaw, or shoulder. This is an example of referred pain. Both cutaneous and visceral sensory neurons here are conducting nerve signals on the same ascending tracts within the spinal cord. The somatosensory cortex in the brain is unable to accurately determine the actual source of the stimulus.

3. If the SA node is not functioning, the AV node will function as an ectopic pacemaker. The typical rate of spontaneous depolarizing for the AV node is 40 to 50 times per minute. The action potential will spread along the conduction system to cause the ventricles to contract. Because the atria are stimulated to contract by the SA node and it is no longer functioning, the atria do not contract. (Note, however, that 70% of the filling of the ventricles is passive (meaning that when the AV valves open, the blood within the atria just ‘falls’ into the ventricles. There is a reduced volume in the ventricles, but blood is still being circulated.)

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Chapter 20 Answers to “What Did You Learn?”

1. Compared to their venous companions, arteries have 1) a thick tunica media, 2) a narrower lumen, and 3) more elastic and collagen fibers.

2. As arteries branch to progressively smaller vessels their luminal diameter decreases. The composition of the tunics also changes; their walls contain relatively less elastic fibers and relative more smooth muscle.

3. Sinusoids are the most permeable capillaries. They are located within red bone marrow as well as the liver, spleen, anterior pituitary gland, and parathyroid glands. (A common feature is their reddish color.)

4. Because veins contain about 55% of systemic blood within the body, they serve as blood reservoirs. When more blood is needed with increased physical exertion, blood may be shifted from venous reservoirs into circulation through vasoconstriction of veins. When less blood is needed at rest, blood may be shifted back into venous reservoirs through vasodilation of veins.

5. There are four alternatives to a simple pathway of blood flow. The simple pattern involves blood through one artery, capillary bed, and vein associated with an organ or body region. The alternative pathways are: 1) an arterial anastomosis, which includes two or more arteries converging to supply the same body region, 2) a venous anastomosis, which includes two or more veins draining the same body region, 3) an arteriovenous anastomosis, which is a shunt that transports blood from an artery directly into a vein, bypassing the capillary bed, and 4) a portal system, which involves the movement of blood through two capillary beds, with the two capillary beds separated by a portal vein.

6. Blood flow velocity is slowest in capillaries. Although a single capillary has the smallest cross-sectional area, the total (aggregate) cross-sectional area of all capillaries is the largest for all types of blood vessels. It is physiologically significant because of its influence on blood flow velocity. Blood flow velocity in capillaries is relatively slow, and this allows sufficient time for efficient capillary exchange of nutrients, respiratory gases, hormones, and wastes between the tissues and the blood.

7. Substances such as oxygen, hormones, nutrients, carbon dioxide, and waste products enter or leave capillaries by diffusion. Solutes such as certain hormones (e.g., insulin) and fatty acids are transported across the endothelial cell membranes by vesicular transport.

8. Hydrostatic pressure is the physical force exerted by a fluid on a structure. In contrast, osmotic pressure is the “pull” of water into an area by osmosis due to the higher relative concentration of solutes.

9. Blood hydrostatic pressure is greater at the arterial end of the capillary (35 mm Hg) and less at the venous end (16 mm Hg). In contrast, the net colloid osmotic pressure remains relatively constant (21 mm Hg) at both the arterial and venous ends of the capillary.

10. The blood hydrostatic pressure (HPb) is the greatest force at the arterial end of the capillary. A positive value is calculated for the net filtration pressure on the arterial end of a capillary; this reflects fluids being forced out of the capillary (filtration) on the arterial end of a capillary. The blood colloid osmotic pressure (COPb) is the greatest force at the venous end of the capillary. A negative value is calculated for the net filtration pressure on the venous end of a capillary; this reflects fluids being pulled into the capillary (reabsorption).

11. Without functional lymphatic vessels, the excess 15% of fluid is not reabsorbed by capillaries; fluid would accumulate in the interstitial space.

12. Angiogenesis is the formation of new blood vessels in tissues that require them. Angiogenesis is stimulated in skeletal muscle in response to aerobic training. In adipose tissue angiogenesis occurs when an individual gains weight in the form of fat deposits.

13. Blood flow into a tissue remains relatively constant because of the myogenic response, which is the contraction and relaxation of smooth muscle in response to changes in stretch. If there is an increase in systemic

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blood pressure, an additional volume of blood enters the vessel resulting in the stretching of vessel wall smooth muscle cells. In response the smooth muscle cells contract causing vasoconstriction. Decreased size of the vessel lumen offsets the change and blood flow into the tissue remains constant.

14. Local regulation of blood flow continuously occurs in response to changes in tissue metabolic activity. The stimulus for the response is changing concentrations of certain chemicals (termed vasoactive chemicals).

Vasodilators act to increase blood flow into a capillary bed whereas vasoconstrictors act to decrease blood flow into a capillary bed. As metabolic activity increases, there is a change in chemical composition in the tissue that cause vasodilation (e.g., decrease in O2 and nutrients, increased CO2, lactate, H+, and K+ levels); arterioles dilate and precapillary sphincters relax allowing additional blood through the capillary bed.

15. Total blood flow is the amount of blood transported throughout the entire vasculature in a given period of time. It equals cardiac output. As total blood flow increases, additional blood is available to body tissues and local blood flow increases.

16. The pulse pressure is 60 mm Hg (155 mm Hg – 95 mm Hg = 60 mm Hg). The mean arterial pressure is 115 mm Hg (95 mm Hg + [1/3 × 60 mm Hg] = 95 + 20 =115 mm Hg. 17. Capillary blood pressure must be sufficient for exchange of substances between the blood and surrounding tissue, but not be so high that it would damage the fragile vessels.

18. The relatively small pressure gradient (only 20 mm Hg) of veins is overcome by the skeletal muscle pump and the respiratory pump. The skeletal muscle pump assists the movement of blood primarily within the limbs.

Skeletal muscles there contract, which squeezes veins to help propel the blood toward the heart. This movement is restricted to only one direction by one-way venous valves within the veins. The respiratory pump assists movement of blood within the thoracic cavity. During inhalation, 1) the diaphragm contracts/flattens and intrathoracic cavity pressure decreases, and 2) intra-abdominal pressure increases and places pressure on abdominal cavity vessels. Blood is propelled from the vessels in the abdominopelvic cavity into the vessels in the thoracic cavity. Exhalation reverses the pressure differences so that blood moves from vessels in the thoracic cavity back into the heart (and allows blood to move from the vessels within the lower limbs into the blood vessels within the abdominal cavity).

19. The pressure gradient of systemic circulation is calculated by subtracting the mean arterial pressure in the vena cava from the mean arterial pressure in the arteries near the aorta. This blood pressure gradient is the driving force to move blood through the vasculature. Changes in the blood pressure gradient are directly correlated with changes in total blood flow.

20. Resistance is defined as the amount of friction the blood experiences as it is transported through the blood vessels. (This friction is due to the contact between blood and the blood vessel wall.)

21. The three factors that alter resistance are 1) blood viscosity, 2) vessel length, and 3) vessel radius. Viscosity is the resistance of a fluid to its flow. Increase in fluid viscosity causes an increase in its resistance to flow. A similar relationship exists between vessel length and resistance. The longer the vessel, the greater the friction the fluid experiences as it travels through the vessel. In contrast, there is an inverse relationship between the diameter of blood vessels and resistance. As vessel diameter increases, the resistance to flow decreases.

22. Individuals with sustained increased resistance generally exhibit elevated arterial blood pressure readings.

This condition occurs because a greater pressure gradient must be produced to overcome the higher resistance and ensure normal blood flow and adequate perfusion of all tissues.

23. Short-term mechanisms for regulating blood pressure involve the nervous system and are important when quick adjustment of blood pressure must occur as when a person rises from a sitting to a standing position.

24. As a person arises in the morning her blood pressure will initially drop, but then it will quickly be reestablished to normal levels throughout the following mechanism: 1) Decreased stretch in the blood vessel wall is detected by baroreceptors in aortic arch baroreceptors and carotid sinuses. 2) The baroreceptors decrease their

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firing rate along the vagus and glossopharyngeal nerves, signaling the cardiac center and vasomotor center in the medulla oblongata. 3) The cardioacceleratory center of the cardiac center increases stimulation to the SA node, AV node, and myocardium, while at the same time the cardioinhibitory center decreases parasympathetic stimulation to the SA and AV nodes. The resulting increase in both heart rate and stroke volume produces a greater cardiac output. 4) Simultaneously, the vasomotor center stimulates vasoconstriction and an increase in peripheral resistance, along with a shifting of blood from venous reservoirs. The resulting increase in cardiac output, increase in resistance, and larger circulating blood volume quickly elevate blood pressure.

25. The liver continuously produces an inactive protein called angiotensinogen and releases it into the blood.

Renin is an enzyme produced by the kidneys that is released into the blood when the kidney is stimulated, either by low blood pressure or the sympathetic division. Within the blood, renin converts angiotensinogen into angiotensin I. Angiotensin I is then converted to angiotensin II by angiotensin-converting enzyme, which is found primarily within the endothelium of capillaries in the lungs. Angiotensin II has several effects: it 1) raises blood pressure by causing vasoconstriction, 2) stimulates the thirst center to cause a sensation of thirst, and 3) induces the release of aldosterone and antidiuretic hormone. Since both of these hormones cause fluid retention in the kidneys, they increase blood volume and therefore raise blood pressure.

26. Atrial natriuretic peptide 1) vasodilation, which lowers the total peripheral resistance, and 2) increases urine production, which decreases blood volume. Both responses lower blood pressure.

27. During exercise blood is increased primarily to the coronary vessels that supply the heart wall, skeletal muscles, and skin, and decreased to the abdominal organs, including those of the digestive system as well as the kidneys.

28. All (100%) of the blood returning from the systemic circuit must be pumped to the pulmonary circuit to pick up oxygen and release carbon dioxide.

29. Blood pressure is lower throughout the pulmonary circulation in comparison to the systemic circulation because pulmonary vessels are shorter and the lungs are close to the heart so the pressure to drive the blood through the circuit does not have to be as high.

30. The three branches extending from the aortic arch are: 1) the brachiocephalic trunk that supplies blood to the right arm, the right side of the face, and the brain, 2) the left coronary artery that supplies blood to the left side of the face and the brain, and 3) the left subclavian artery that provides blood to the left arm.

31. The superior vena cava drains the head, neck, upper limbs, and thoracic and abdominal walls. The inferior vena cava drains blood from the lower limbs, pelvis, perineum, and abdominal structures.

32. The major arteries that serve the head include the common carotid arteries and vertebral arteries. These regions are then drained by the internal jugular veins, external jugular veins and vertebral veins.

33. The dural venous sinuses drain most of the venous blood of the cranium. These are large modified veins formed between the two layers of dura mater and they also receive excess cerebrospinal fluid. Blood from the dural venous sinus system is drained primarily into the internal jugular veins.

34. The azygous system drains into the superior vena cava.

35. The bronchi, bronchioles, and connective tissue of the lungs are supplied with oxygenated blood by three or four small bronchial arteries. The smaller structures of the respiratory passageway (e.g., alveoli) obtain oxygen directly from the inspired air.

36. The celiac trunk branches into the left gastric artery, splenic artery, and the common hepatic artery. The left gastric artery supplies blood to parts of the stomach and esophagus. The splenic artery supplies blood to the spleen, part of the stomach and pancreas. The common hepatic artery supplies blood to the liver, gallbladder, duodenum, as well as to parts of the pancreas and stomach.

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37. The splenic, inferior mesenteric, and superior mesenteric veins drain into the hepatic portal system. The hepatic portal system drains blood from digestive organs and the spleen into the liver before the blood drains to the inferior vena cava.

38. The kidneys receive blood through the renal arteries. The adrenal glands receive blood from the renal, middle suprarenal, and inferior phrenic arteries. The female uterus receives blood through the uterine artery.

39. From the subclavian artery blood will flow through the axillary artery, the brachial artery, then through either the ulnar or radial arteries to the deep palmar arch, and finally to the digital arteries of the thumb.

40. The primary superficial veins of the upper limbs include the basilic, cephalic, and median cubital veins.

41. Blood flow pathway from the external iliac to the digital arteries would be: the external iliac artery  the femoral artery  the popliteal artery  the anterior tibial artery the dorsal pedis artery  the plantar arterial arch  and finally the digital arteries of the foot.

42. The dorsal venous arch drains into the great saphenous vein and small saphenous vein. The great saphenous vein originates in the medial ankle and extends adjacent to the medial surface of the entire lower limb before it drains into the femoral vein. The small saphenous vein extends adjacent to the lateral ankle and travels only along the posterior calf before draining into the popliteal vein at the level of the knee.

43. 1) The umbilical vein delivers oxygenated blood from the placenta to the fetus. 2) The ductus venosus shunts blood from the umbilical vein to the inferior vena cava, bypassing the fetal liver. 3) Blood is shunted from the right atrium to the left atrium of the fetal heart through the foramen ovale, bypassing the pulmonary circuit. 4) Any blood that does enter the fetal pulmonary circuit is shunted from the pulmonary trunk to the aorta by the ductus arteriosus. 5) Blood returns to the placenta from the fetus through the umbilical arteries.

44. The ductus arteriosus and foramen ovale must close after birth so that all of the blood returning to the right side of the heart is pumped to the lungs for gas exchange in the newborn.

Answers to “Do You Know the Basics?”

1. B Feedback: Sinusoids are very unselective, and are not found in the brain.

2. C Feedback: Veins do not have a significant layer of smooth muscle in their tunica media; thus, their thickest tunic is the tunica externa.

3. C Feedback: Vasa vasorum are a network of small arteries in the tunica externa of a large vessel.

4. A Feedback: Decreased blood flow will reduce the amount of blood reaching a region resulting in decreased perfusion.

5. B Feedback: The relatively small pressure gradient of veins is overcome by the respiratory pump and the skeletal muscle pump.

6. B Feedback: Increasing diameter will decrease resistance resulting in an increase in blood flow.

7. D Feedback: Total blood flow is important for maintaining adequate perfusion of a tissue. It increases with increasing pressure, but decreases with increasing resistance.

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8. B Feedback: Blood flow velocity in capillaries is relatively slow because of their relatively large total crosssectional area.

9. D Feedback: Blood pressure is regulated by the cardiovascular center of the medulla oblongata (which is in turn composed of the cardiac center and vasomotor center) through the autonomic nervous system. It can also be adjusted by hormones such as epinephrine, antidiuretic hormone, aldosterone, atrial natriuretic peptide, or angiotensin.

10. D Feedback: From the subclavian artery blood will flow through the axillary artery, the brachial artery, then through either the ulnar or radial arteries.

11. Vessel walls are composed of layers called tunics which surround the vessel lumen. The innermost layer is the tunica intima. It consists of an endothelium (simple squamous epithelium) and a subendothelial layer of areolar connective tissue. The middle tunic, or tunica media, is composed predominantly of layers of smooth muscle. The outermost tunic is the tunica externa and it consists primarily of areolar connective tissue containing elastic and collagen fibers.

12. Arteries transport blood away from the heart. Veins return blood to the heart. Relative to veins, arteries have smaller luminal diameters and experience greater blood pressure. The tunica media is the predominant layer in arteries. Without a significant layer of smooth muscle, veins instead have a thicker tunica externa.

13. Hydrostatic pressure is the physical force exerted by a fluid on a structure. It promotes filtration from the capillary. In contrast, osmotic pressure is the pull of water into an area by osmosis due to the higher relative concentration of solutes. Blood hydrostatic pressure is greater at the arterial end of the capillary (35 mm Hg) and less at the venous end of the capillary (16 mm Hg). In contrast, the net colloid osmotic pressures remain relatively constant (21 mm Hg).

14. NFP = (HPb − HPif) − (COPb − COPif) 15. The major way resistance to blood flow may be regulated is by altering vessel lumen radius. The smaller the vessel radius (thus its diameter), the greater the resistance to blood flow. As a vessel increases in length, resistance to blood flow increases. As blood viscosity increases there is a greater resistance to its blood flow. An inverse relationship is observed between resistance and blood flow. As resistance increases, blood flow decreases and as resistance decreases, blood flow increases.

16. Blood vessels containing smooth muscle cells with α1-adrenergic receptors contract in response to sympathetic stimulation, resulting in vasoconstriction; these include most vessels of the body. In contrast, blood vessels with β2-receptors relax in response to epinephrine (which along with norepinephrine is released from the adrenal medulla in response to stimulation by the sympathetic division), resulting in vasodilation; these include blood vessels in skeletal muscle and the coronary vessels.

17. Increased blood volume, increased cardiac output, and increased resistance will all raise blood pressure.

18. Together the cardiac center and the vasomotor center are called the cardiovascular center. The cardiac center is composed of both the cardioacceleratory center and the cardioinhibitory center. Sympathetic pathways from the cardioacceleratory center extend to the SA node, AV node, and myocardium. Increased nerve signals along these pathways cause release of norepinephrine from the ganglionic neurons, which results in an increase in heart rate and stroke volume and this then increases cardiac output and blood pressure. Parasympathetic pathways from the cardioinhibitory center innervate the SA node and AV node. Increased nerve signals along these pathways cause release of acetylcholine from the ganglionic neurons, which results in a decrease in heart rate.

The vasomotor center regulates the degree of vasoconstriction, generally through sympathetic pathways that extend to most blood vessels of the body. The smooth muscle within the blood vessel walls of the different

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vascularized tissues of the body have either alpha1 receptors (which contract and cause vasoconstriction of the blood vessel in response to stimulation by the sympathetic division) or beta2 receptors (which relax and cause vasodilation of the blood vessel in response to stimulation by the sympathetic division). Consequently, there is a net increase in blood pressure, movement of blood from venous reservoirs, and redistribution of blood flow. (The reverse occurs when there is a decrease in stimulation by the sympathetic division.)

19. In the systemic circulation, systemic arteries carry oxygenated blood away from the heart to tissues and organs throughout the body and veins return deoxygenated blood back to the heart. In the pulmonary circulation, arteries carry deoxygenated blood from the right side of the heart to the lungs (to be reoxygenated) and pulmonary veins bring oxygenated blood back to the left side of the heart. The blood pressure is lower in the pulmonary circulation than in the systemic circulation because blood pressure there need only be sufficient to deliver blood to the adjacent lungs (without potentially causing damage to structures within the lungs).

20. Postnatal changes to the circulatory system include constriction of the umbilical veins (which delivered blood from the placenta to the fetus) and umbilical arteries (which delivered blood from the fetus to the placenta) so they become nonfunctional. The ductus venosus (which was a shunt that bypassed the liver) ceases to be functional and it constricts. Closure of the foramen ovale and ductus arteriosus (which provided a means of bypassing the lungs) occurs because these detours in circulation are no longer needed.

Answers to “Can You Apply What You’ve Learned?”

1. D Feedback: Albumin is the main plasma protein required for establishing the blood colloid osmotic pressure.

Insufficient blood colloid osmotic pressure will prevent the reabsorption of fluid back into the blood resulting in edema.

2. B Feedback: Exercise will cause an increase in blood pressure. Atrial natriuretic peptide lowers blood pressure by causing vasodilation.

3. D Feedback: Decreased blood supply to the brain can cause dizziness and possibly syncope (fainting). The baroreceptors within the carotid detect changes in blood pressure en route to the brain and then signal the cardiovascular center in the medulla oblongata. The cardiovascular center adjusts cardiac output and vasoconstriction accordingly, to maintain adequate blood flow to the brain.

4. A Feedback: The addition of adipose connective tissue (fat) requires angiogenesis, increasing the overall length of the blood vessels (which increases resistance). Increased resistance must be overcome by generating a steeper pressure gradient if adequate perfusion of tissue is to be maintained. Losing fat reduces the total length of blood vessels (which decreases resistance). Thus, decreased resistance can be overcome by generating a smaller pressure gradient to maintain adequate perfusion of tissue.

5. D Feedback: The popliteal artery is the origin of three collateral channels—the anterior tibial, posterior tibial and fibular arteries—which all anastamose at the foot.

Answers to “Can You Synthesize What You’ve Learned?”

1. Atherosclerosis is characterized by the presence of an atheroma which leads to thickening of the tunica intima and narrowing of the arterial lumen. A narrower lumen increases resistance to blood flow and high blood pressure is a result.

2. Flexion at a joint can occlude blood flow through arteries in the region. Anastomoses at joints provide for alternative blood flow pathways when some vessels are occluded due to flexion.

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3. Increased deposits of adipose tissue due to weight gain require angiogenesis to provide blood flow to the new tissue. This increases the total length of the vasculature, and subsequently increases resistance to cardiac output from the heart. As resistance increases, cardiac output must be increased, which raises blood pressure.

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Chapter 21 Answers to “What Did You Learn?”

1. Lymphatic capillaries typically absorb water, dissolved solutes, and small amounts of protein, and sometimes foreign materials including cell debris, pathogens and perhaps metastasized cancer cells.

2. The hydrostatic pressure of interstitial fluid separates the endothelial cells that form the lymphatic capillaries, allowing the interstitial fluid to enter the lymphatic capillary lumen. Once inside the lymphatic capillary, the fluid exerts hydrostatic pressure on the endothelial cells, closing the gaps and trapping the fluid (now called lymph) in the lymphatic capillary.

3. The lymphatic system lacks a pump, and thus it relies on several mechanisms to move lymph through its vessels: 1) contraction of nearby skeletal muscles in the limbs (skeletal muscle pump) and the respiratory pump in the torso (described in chapter 20), 2) the pulsatile movement of blood in nearby arteries, and 3) rhythmic contraction of smooth muscle in walls of larger lymph vessels (trunks and ducts).

4. The right lymphatic duct receives lymph from 1) the right side of the head and neck, 2) the right upper limb, and 3) the right side of the thorax.

5. Primary lymphatic structures, such as bone marrow and the thymus, are involved in the formation and maturation of lymphocytes. Secondary lymphatic structures are not involved in lymphocyte formation, but instead serve to house both lymphocytes and other immune cells following their formation, and they also provide the site where an immune response is initiated. The major secondary lymphatic structures include the lymph nodes, spleen, tonsils, lymphatic nodules, and MALT. 6. Red bone marrow is considered a primary lymphatic structure because it is the site of production of all formed elements in the blood, including all lymphocytes, whereas secondary lymphatic structures house lymphocytes following their formation.

7. Each lobule of the thymus is arranged into an outer cortex and inner medulla. The cortex of the thymus contains immature T-lymphocytes (pre-T-lymphocytes) and the medulla contains mature T-lymphocytes.

8. Numerous afferent lymphatic vessels will deliver lymphatic fluid to a lymph node. The “collective diameter” of the numerous afferent vessels is greater than the diameter on the single efferent vessel, resulting in the generation of a higher fluid pressure to help force the lymph through the node. As the materials within the fluid percolate through the sinuses located within the medulla of the lymph node, they will be exposed to macrophages and lymphocytes. Macrophages will remove foreign particles from the lymphatic fluid. Lymphocytes may be stimulated to initiate an immune response upon exposure to the foreign particles.

9. The spleen filters the blood. Trabeculae from the connective tissue capsule around the spleen extend into it to partition the spleen into white pulp (clusters of T-lymphocytes, B-lymphocytes and macrophages) and red pulp (houses erythrocytes, platelets, macrophages and B-lymphocytes) that forms cords of cells with associated sinusoids. It serves several functions: 1) phagocytosis of bacteria and other foreign materials for body defense (red pulp and white pulp), 2) phagocytosis of old, defective erythrocytes and platelets from circulating blood (red pulp), and 3) creating a blood reservoir and storage site for both erythrocytes and platelets (red pulp).

10. Lymph nodes filter lymph, whereas the spleen filters blood.

11. The three main groups of tonsils are the pharyngeal, palatine, and lingual tonsils. Tonsils function to help protect against foreign substances that may be either inhaled or ingested.

12. The lymphatic cells in the MALT help defend against foreign substances that come in contact with mucosal membranes.

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Answers to “Do You Know the Basics?”

1. B Feedback: The lymphatic system returns excess fluid to the blood to maintain fluid balance and blood pressure (thus, supporting the cardiovascular system). It also houses lymphocytes and macrophages to defend against foreign substances (thus, supporting the immune system).

2. B Feedback: The right lymphatic duct drains lymph from the right side of the head, neck, right arm, and the right side of the thoracic cavity.

3. D Feedback: The spleen is inferior to the diaphragm and adjacent to the stomach.

4. A Feedback: Although immature T-lymphocytes originate within red bone marrow, they complete maturation within the thymus.

5. B Feedback: Lymphatic capillaries are homologous with blood capillaries in that they consist of a simple endothelial layer, although they are typically larger in diameter. Unlike blood capillaries, they also possess overlapping endothelial cells that act as one-way flaps to allow interstitial fluid to enter the lymphatic system.

6. C Feedback: Numerous lymphatic vessels will deliver lymphatic fluid to a lymph node. As the materials within the fluid percolate through the sinuses located in the medulla of the lymph node, they will be exposed to macrophages and lymphocytes. Division of lymphocyte in response to an infection may cause the lymph node to swell and become tender.

7. B Feedback: The spleen will not be swollen early in a Streptococcus infection of the throat.

8. C Feedback: The body region drained by the subclavian trunk is the upper limbs, breasts and superficial thoracic wall.

9. D Feedback: The spleen is responsible for removing old or defective formed elements such as erythrocytes and platelets from the blood.

10. D Feedback: Numerous lymphatic vessels will deliver lymphatic fluid to a lymph node. As the materials within the fluid percolate through the sinuses of the lymph node, they will be exposed to macrophages and lymphocytes.

11. The lymphatic system is composed of: 1) lymph vessels (lymphatic capillaries, lymphatic vessels, lymphatic trunks, and lymphatic ducts), 2) primary lymphatic structures (red bone marrow and the thymus), and 3) secondary lymphatic structures (lymph nodes, spleen, tonsils, lymphatic nodules and MALT).

12. Primary lymphatic structures are involved in the formation and maturation of lymphocytes. They include: bone marrow and the thymus. Secondary lymphatic structures include the lymph nodes, spleen, tonsils, lymphatic nodules, and MALT. They are not involved in formation of lymphocytes but instead serve to house both lymphocytes and other immune cells following their formation.

13. Lymph is interstitial fluid that passively enters lymphatic capillaries. Flowchart: lymphatic capillary  lymphatic vessels  lymph nodes  lymphatic trunks  lymphatic ducts  venous blood.

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14. The thoracic duct drains lymph from the left side of the head and neck, left upper limb, left thorax, all of the abdomen and both lower limbs.

15. The thymus continues to grow until puberty, when it reaches a maximum weight of 30 to 50 grams. Cells within the thymus begin to regress after it reaches this size. Thereafter, much of the thymic tissue is replaced by adipose connective tissue.

16. Lymph nodes are small, round or oval encapsulated structures located along the pathways of lymph vessels where they serve as the main lymphatic organ. Numerous afferent lymphatic vessels will bring lymph into a lymph node. Lymph passes through the node sinuses located in the medulla of the lymph node and then exits through the one efferent lymphatic vessel. The function of the node is to expose lymph to macrophages and lymphocytes within the node. Macrophages will remove foreign particles from the lymphatic fluid. Lymphocytes will initiate an immune response upon exposure to the foreign particles.

17. The spleen is surrounded by a connective tissue capsule from which trabeculae extend into the organ. It lacks a cortex and medulla, but the trabeculae subdivide the spleen into red pulp and white pulp. The red pulp is found within sinusoids. It contains erythrocytes, platelets, macrophages, and B-lymphocytes. These cells are housed in reticular connective tissue and form structures called splenic cords. The red pulp serves as a blood reservoir, including a storage site for both erythrocytes and platelets, and also removes old erythrocytes and platelets from circulation. The white pulp consists of spherical clusters of T-lymphocytes, B-lymphocytes, and macrophages which surround a central artery. Lymphatic cells within the white pulp monitor the blood for foreign materials, bacteria, and other potentially harmful substances.

18. A pharyngeal tonsil is found in the posterior wall of the nasopharynx, palatine tonsils are located in the posterolateral region of the oral cavity, and the lingual tonsils are located along the posterior one third of the tongue.

19. Lymphatic nodules are small, oval clusters of lymphatic cells with some extracellular matrix that are not completely surrounded by a connective tissue capsule. They are found within every organ of the body and within the wall of the appendix. In some areas of the body, many lymphatic nodules will group together to form larger structures, such as MALT. 20. The lymphatic system aids the cardiovascular system by returning excess fluid to the blood to maintain fluid balance, blood volume, and blood pressure. It also provides support to the immune system by transporting and housing lymphocytes and other immune cells that help the immune system defend against foreign substances.

Answers to “Can You Apply What You’ve Learned?”

1. A Feedback: Lymph from the head must drain through lymph nodes in the cervical region.

2. D Feedback: The thymus is responsible for the maturation of T-lymphocytes.

3. B Feedback: The spleen is responsible for filtering pathogens including bacteria from the blood.

4. A Feedback: Axillary lymph nodes, which drain fluid from the arms and axilla, are often removed during a mastectomy.

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5. D Feedback: Obstruction or removal of lymph nodes or scarring of lymphatic vessels will inhibit drainage of fluid by the lymphatic system. Exercise will cause increased hydrostatic pressure in blood capillaries, which will cause an increase in interstitial fluid. This fluid will produce greater hydrostatic pressure on lymph capillaries, forcing the fluid into lymph capillaries, therefore preventing edema.

Answers to “Can You Synthesize What You’ve Learned?”

1. The doctor was checking for an enlargement of her spleen. The white pulp of the spleen contains lymphocytes which monitor the blood for pathogens, and are capable of initiating an immune response. The red pulp within the sinusoids of the spleen contains macrophages, which remove foreign substances, or pathogens. Activation of B-lymphocytes causes them to proliferate (go through cellular division) in the white pulp in response to mononucleosis, which may cause an enlargement of the organ.

2. Lymphatic capillaries are highly unselective. Filtration in the lymphatic system does not occur until lymph reaches the lymph nodes. Cancer cells can enter lymphatic capillaries and establish new tumors within lymph nodes.

3. Medical guidelines suggest performing a tonsillectomy only if the person has had seven throat infections in 1 year, five infections in 2 years, or three infections per year for 3 years.

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Chapter 22 Answers to “What Did You Learn?”

1. Viruses are not cells, and must enter a cell in order to replicate. Bacteria are called prokaryotic cells.

2. T-lymphocytes, B-lymphocytes, macrophages, dendritic cells and NK cells are housed in lymph nodes; thus, these are the cells lymph has contact with as it is filtered through lymph nodes.

3. Cytokines are small, soluble proteins produced by cells of both the innate and adaptive immune systems to regulate and facilitate immune system activity. Cytokines are similar to hormones in that they are released from one cell and bind to a specific receptor on a target cell. They can act on the cell that released it, local neighboring cells, or circulate in the blood to cause systemic effects.

4. The cells of adaptive immunity are T-lymphocytes and B-lymphocytes.

5. Both the skin and mucosal membranes provide a physical, chemical and biological barrier to prevent entry of potentially harmful agents.

6. Both neutrophils and dendritic cells (as well as macrophages) are phagocytic cells. Dendritic cells (along with macrophages) also serve the role of the antigen-presenting cell (engulf foreign substances, digest them into peptide fragments and present them with MHC molecules to T-lymphocytes).

Basophils and mast cells both release granules that contain various substances including histamine (which increases both vasodilation and capillary permeability) and heparin (an anticoagulant). They also release eicosanoids from their plasma membrane that illicit an inflammatory response. However, basophils are within the blood and mast cells are within connective tissue.

7. NK cells make physical contact with unhealthy cells and destroy them by release of cytotoxic chemicals.

These cytotoxic chemicals include perforin, which forms a transmembrane pore in the unwanted cells, and granzymes which then enter the cell through the perforin hole initiating apoptosis (programmed cell death).

8. The complement system consists of one of the most important antimicrobial groups of substances of innate immunity. It is composed of at least 30 plasma proteins that are collectively referred to as complement. The name is derived from how they work along with antibodies. The four major means by which the complement system functions in innate immunity include: 1) opsonization, 2) inflammation, 3) cytolysis, and 4) the elimination of immune complexes.

9. Inflammation is an immediate, local, nonspecific event that occurs in vascularized tissue against a great variety of injury-causing stimuli. The steps in the inflammatory response are: 1) the release of inflammatory and chemotactic factors from damaged cells of injured tissue; 2) vascular changes including a) vasodilation of arterioles, b) increase in capillary permeability, and c) display of CAMs in capillary endothelium; 3) recruitment of immune cells via margination, diapedesis, and chemotaxis; and 4) delivery of plasma proteins to the injured or infected site.

10. Exudate delivers cells and substances needed to eliminate the injurious agent and promote healing. It also promotes additional fluid uptake by lymphatic capillaries, which facilitates the removal of unwanted substances from the site of infection (e.g., infectious agents, dead cells, cellular debris).

11. A fever is defined as an abnormal elevation of body temperature of at least 1°C from the typically accepted core body temperature (37°C). The stages of a fever are: 1) onset - the hypothalamus stimulates blood vessels in the skin to retain heat through vasoconstriction, as well as shivering in order to generate more heat; 2) stadium - the metabolic rate increases to promote physiologic processes involved in eliminating harmful substances; and 3) defervescence - the temperature returns to its normal set point, as the hypothalamus is no longer stimulated to maintain the higher body temperature. Body temperature is lowered through sweating and vasodilation of blood vessels in the skin.

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12. The benefits of a fever are: a fever inhibits reproduction of bacteria and viruses, promotes interferon activity, increases activity of adaptive immunity, and accelerates tissue repair. Fevers can be potentially dangerous because of changes to metabolic pathways and denaturation of body proteins. Seizures may occur at sustained body temperatures above 102oF, irreversible brain damage may occur at body temperatures that are sustained at greater than 106oF, and death is likely when body temperature reaches 109oF. 13. An antigen is a substance that binds to a component of adaptive immunity. The specific site on the antigen molecule that is recognized by components of the immune system is referred to as the antigenic determinant.

14. Haptens are too small to trigger a response by the immune system (unlike an antigen, which can). A hapten must first bind to a carrier molecule before it can become an antigenic and induce in an immune response. Examples of haptens include oil in poison ivy and pollen.

15. The receptor complexes of T-lymphocytes (TCR or T-cell receptor) and B-lymphocytes (BCR or B-cell receptor) differ in that BCRs are capable of making direct contact with antigen, whereas TCRs are not. A TCR requires initial processing and presentation of the antigen in the plasma membrane of another type of cell before making contact. T-lymphocytes also possess additional receptor molecules (called coreceptors) that facilitate Tlymphocyte physical interaction with a cell presenting antigen. A significant category is the CD molecules. Helper T-lymphocytes contain the CD4 protein of the coreceptor. Cytotoxic T-lymphocytes contain the CD8 protein of the coreceptor.

16. All nucleated cells (all cells except erythrocytes) present antigen with MHC class I molecules. (If infected they are alerting a cytotoxic T-lymphocyte that it needs to be destroyed.) Antigen-presenting cells (which include macrophages, dendritic cells, and B-lymphocytes) have both MHC class I and MHC class II. MHC class I molecules are used to present antigen to cytotoxic T-lymphocytes (CD8+ cells), whereas MHC class II molecules are used to present antigen to helper T-lymphocytes (CD4+ cells).

17. Lymphocytes typically encounter antigens for the first time within secondary structures including the lymph nodes, spleen, tonsils, and MALT. 18. Maturation of T-lymphocytes takes place in the thymus.

19. A T-lymphocyte that fails negative selection has the potential of initiating an autoimmune response (immune response against self antigens).

20. Central tolerance is a process of negative selection in which cells learn to ignore self-antigens. It takes place in the primary lymphatic structures. Peripheral tolerance is the process whereby T-regulatory lymphocytes (Tregs) function in self-tolerance outside of the primary lymphatic structures.

21. Helper T-lymphocytes are required by both.

22. Helper T-lymphocytes release IL-2, which serves as a) an autocrine hormone that stimulates itself and b) a paracrine hormone that stimulates cytotoxic T-lymphocytes. Interleukin-2 released from helper Tlymphocytes stimulates the cells to proliferate into activated helper T-lymphocytes and memory helper Tlymphocytes. Similarly, IL-2 from helper T-lymphocytes stimulates cytotoxic T-lymphocytes to divide and differentiate into clones, activated cytotoxic T-lymphocytes, and memory cytotoxic T-lymphocytes.

23. B-lymphocytes do not require antigen to be presented by other nonlymphocyte cells. A B-lymphocyte responds to antigens outside of the cells (serving the role of the antigen-presenting cell).

24. Cytokine (specifically IL-4) released from helper T-cells stimulates B-lymphocytes to proliferate.

They then differentiate into either activated B-lymphocytes or memory B-lymphocytes.

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25. Lymphocyte recirculation provides a means of delivering different lymphocytes to secondary lymphatic structures, making it more likely that a lymphocyte will encounter its antigen, if present.

26. Yes, helper T-lymphocytes release IL-2 and other cytokines that regulate cells of both adaptive and innate immunity.

27. Cell-mediated immunity is effective against unhealthy cells, such as virus-infected cells, bacteriainfected cells, or tumor cells, and also against foreign transplanted cells.

28. Plasma cells (differentiated B-lymphocytes) remain in lymph nodes and continue to synthesize and release antibodies against specific antigens.

29. The variable regions located at the ends of the arm of the antibody contain the antigen-binding site, which attach to a specific antigenic determinant of an antigen.

30. The six major functions of antibodies include: neutralization, agglutination, precipitation, complement fixation, opsonization, and activation of NK cells. The functions that occur due to antigen binding are neutralization, agglutination and precipitation. The functions that depend upon the Fc region are complement fixation, opsonization, and activation of NK cells.

31. IgG is the most prevalent class of immunoglobulins. IgG immunoglobulins have the most diverse range of function, including: neutralization of viruses, bacteria, and toxins; agglutination; precipitation; complement activation; opsonization; and natural killer cell activation.

32. An initial antigen challenge causes the production of memory B- and T-lymphocytes. On subsequent exposures to the antigen, these memory cells make contact with the antigen more rapidly and produce a more powerful response.

33. Secondary responses have a much shorter lag phase, with antibody production rising more rapidly, when compared to a primary response. The higher level of IgG production may continue for longer periods, perhaps even years.

34. Active immunity results in the production of memory cells and provides longer protection from an antigen.

Answers to “Do You Know the Basics?”

1. B Feedback: T-lymphocytes are not phagocytic; they are involved in cell-mediated adaptive immunity.

2. B Feedback: Helper T-lymphocytes release cytokines, which induces the differentiation and proliferation of B-lymphocytes.

3. C Feedback: An immunocompetent, naive B-lymphocyte first binds free antigens, which it processes and presents to an activated helper T-lymphocyte via a MHC class II molecule. The helper T-lymphocyte then releases interleukin-4, which stimulates the differentiation of B-lymphocytes into populations of memory and activated cells.

4. A Feedback: Both NK cells and cytotoxic T-lymphocytes release cytokines that trigger apoptosis in target cells.

5. B Feedback: The antibody binds antigen and elicits a specific response, but it does not destroy the antigen.

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6. D Feedback: Lymphocytes are very specific for specific antigens.

7. C Feedback: During inflammation, both vasodilation and increased permeability of capillaries allow extra fluid from blood to wash through the affected area, before being drained by lymphatic capillaries.

8. A Feedback: Interferon is released from cells infected with viruses, stimulating an immune response, and helping to protect neighboring cells from infection.

9. D Feedback: After formation in red bone marrow, immune cells must be activated in secondary lymphatic organs, and only then can they participate in immunologic defense at the site of infection.

10. A Feedback: Complement helps to elicit an inflammatory response and cytolysis.

11. Innate immunity is nonspecific and it provides an immediate response to a wide array of infectious or toxic substances. It utilizes protective barriers such as mucous and cutaneous membranes, macrophages, and cytotoxic NK cells. Nonspecific events such as inflammation and fever are also involved. Adaptive immunity, although initially a slower response, allows the body to learn to recognize specific antigens, thereby providing for a faster defense upon subsequent exposures. Adaptive immunity requires the interactions of T-lymphocytes and B-lymphocytes.

12. Inflammation is an immediate, local, nonspecific event that occurs in vascularized tissue against a variety of injury-causing stimuli. The first step in the immune response is the release of various chemicals. Damaged cells of injured tissue, including basophils, dendritic cells, macrophages, mast cells, and infectious organisms release numerous chemicals. These chemicals include histamine, leukotrienes, prostaglandins, interleukins, TNFs, and chemotactic factors are released at the site of the injury. The chemical release is followed by vasodilation and increased capillary permeability at the site. Increased fluid within the tissue facilitates the recruitment of immune cells from the blood into the interstitial space, as well as the release of immunoglobulins and clotting proteins. The additional fluid also helps to remove cellular debris and pathogens into the lymphatic system.

13. An antigen is a substance that binds to a component of adaptive immunity, a T-lymphocyte or an antibody.

14. Major histocompatibility complexes (MHC molecules) are glycoproteins that bind antigens. All nucleated cells (all cells except erythrocytes) present antigen with MHC class I molecules. (If infected they are alerting a cytotoxic T-lymphocyte that it needs to be destroyed.) Antigen-presenting cells (which include macrophages, dendritic cells, and B-lymphocytes) have both MHC class I and MHC class II. MHC class I molecules are used to present antigen to cytotoxic T-lymphocytes (CD8+ cells), whereas MHC class II molecules are used to present antigen to helper T-lymphocytes (CD4+ cells).

15. Positive selection selects for T-lymphocytes that bind with thymic epithelial cells that have MHC molecules.

Negative selection eliminates T-lymphocytes that target self-antigens that are present within an MHC molecule.

16. Helper T-lymphocytes regulate and enhance formation and activity of cells of the innate immune system through the release of cytokines, and thus they play a central role in a normal functioning immune system.

17. Cytotoxic T-lymphocytes recognize antigens presented by infected cells, and destroy the infected cells by inserting perforin protein into their plasma membranes and then introducing granzymes into the cells to induce apoptosis.

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18. The other major functions of antibodies include: neutralization, agglutination, precipitation, complement fixation, opsonization, and activation of NK cells. The functions that occur due to antigen binding are neutralization, agglutination and precipitation. The functions that depend upon the Fc region are complement fixation, opsonization, and activation of NK cells. Activated complement can cause opsonization of bacteria, inflammation, cytolysis via membrane attack complexes, or the elimination of immune complexes by binding them to erythrocytes.

19. Cell-mediated immunity (or cellular immunity) is the immune response involving T-lymphocytes which differentiate into helper T-lymphocytes and cytotoxic T-lymphocytes are effective against unwanted cells (e.g., virus-infected cells, bacteria, cancer cells), whereas humoral immunity involves B-lymphocytes, which are effective against antigen outside of cells (e.g., a viral particle).

20. The primary response is the measurable response of antibody production to the first exposure to a foreign antigen. There is a lag/latent phase before detectable antibody production. Secondary responses have a much shorter lag phase, with antibody production rising very quickly, when compared to a primary response. During secondary responses the pathogen is typically eliminated even before disease symptoms develop.

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: Inflammation is a generalized, local response to damage, a toxin, or an infection. It is characterized by the release of fluid into the tissue.

2. A Feedback: The function of a vaccine is to stimulate the immune system to develop memory B-lymphocytes, while providing a relatively safe means for the initial exposure to a microorganism.

3. B Feedback: HIV infects and destroys helper T-lymphocytes over a period of time. Prolonged HIV infection leads to acquired immunodeficiency syndrome (AIDS).

4. D Feedback: Humoral immunity is the production of antibodies, a process mediated by B-lymphocytes.

5. C Feedback: Cell-mediated immunity does not utilize antibodies to target the cells of pathogens or pathogen-infected cells. Humoral immunity utilizes antibodies which are capable of targeting subcellular structures such as viruses.

Answers to “Can You Synthesize What You’ve Learned?”

1. Damage to a tissue may result from chronic irritation that may cause the release of inflammatory and chemotactic factors from damaged cells. This is followed by vasodilation and increased capillary permeability at the site, producing excessive interstitial fluid. The additional fluid helps to remove cellular debris into the lymphatic system. The pressure caused by the increase in fluid in the area is causing Dianne’s pain.

2. A fever inhibits reproduction of bacteria and viruses, promotes interferon activity, increases activity of adaptive immunity, and accelerates tissue repair.

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3. There are three major phases associated with an allergic reaction (such as to ragweed): a) Sensitization phase. An individual is exposed to ragweed, which is engulfed by an antigen-presenting cell (APC) and presented to a helper T-lymphocyte. The helper T-lymphocytes release cytokines that cause the Blymphocytes to mature into plasma cells, which then produce IgE antibodies against the ragweed. The IgE antibodies bind to basophils and mast cells (by the Fc region of the antibody), and may remain bound to these cells for several weeks or longer. (b) Activation phase. If the individual is reexposed to ragweed, the ragweed binds to the IgE antibodies that are bound to the basophils and mast cells, cross-linking the receptors. (c) Effector phase. The mast cells or basophils release chemicals (histamine, heparin, and eicosanoids) that cause an inflammatory response. The inflammatory response is responsible for the symptoms associated with allergies. Contact with the mucous membranes of the nasal passage and conjunctiva of the eye result in a runny nose and watery eyes (allergic rhinitis, or “hay fever”).

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Chapter 23 Answers to “What Did You Learn?”

1. Alveoli are associated with the exchange of respiratory gases.

2. The nose, nasal cavity, and pharynx compose the upper respiratory tract. Structures that participate in gas exchange with the blood -- including the respiratory bronchioles, alveolar ducts, and alveoli -- are the structures that compose the respiratory zone.

3. A general pattern of structural change is observed in the epithelium along the length of the respiratory tract.

The epithelium lining the nasal cavity is a pseudostratified ciliated columnar epithelium with goblet cells (that function in producing mucus), whereas the epithelium lining the alveolar ducts and alveoli is a simple squamous epithelium.

4. Air is warmed, cleansed, and humidified as it passes through the nasal cavity.

5. The nasal conchae (which are three paired projections on the lateral walls of the nasal cavity form an uneven surface in the nasal cavity) cause the air turbulence (the air to swirl) as it moves through the nasal cavity. This increases the amount of contact between the inhaled air and the mucous membranes lining the nasal cavity, which facilitates the conditioning of the inhaled air.

6. Paranasal sinuses are spaces within the skull bones. Ducts connect the paranasal sinuses to the nasal cavity.

7. The nasopharynx contains both the lymphatic nodules called the tubal tonsils and the single pharyngeal tonsil. The oropharynx contains the paired palatine tonsils on its lateral walls and the lingual tonsils at the base of the tongue.

8. The epiglottis of the larynx closes over the opening of the larynx so air cannot escape and simultaneously abdominal muscles contract to increase abdominal pressure. This action is referred to as the Valsalva maneuver.

9. The three unpaired cartilages in the larynx are the epiglottis, thyroid cartilage, and cricoid cartilage.

10. The vocal folds consist of vocal ligaments (elastic connective tissue) that extend between the thyroid cartilage and the arytenoid cartilages. The ligaments are covered with a mucous membrane to form the vocal folds. Vocal folds produce sound when air passes between them and for this reason are also called the true vocal cords. The vestibular folds consist of vestibular ligaments that extend between the thyroid cartilage to the arytenoids and corniculate cartilages. The ligaments are covered with a mucosa. The vestibular folds are located superiorly to the vocal folds and serve to protect the vocal folds as air moves into the larynx. Because vestibular folds have no function in sound production, they are also called the false vocal cords.

11. These C-shaped tracheal cartilages reinforce and provide structural support for the anterior and lateral walls of the trachea to ensure that the trachea remains open (patent). The more flexible trachealis muscle and ligamentous membrane on the posterior aspect of the trachea allows for distension during swallowing of food through the esophagus. In addition, the trachealis muscle contracts during coughing to reduce the diameter of the trachea, thus facilitating the more rapid expulsion of air, helping to dislodge material (foreign objects or food) from the air passageway.

12. Bronchi have incomplete rings or plates of hyaline cartilage to support their walls and ensure that they remain open. Unlike bronchi, bronchioles have no cartilage in their walls, because their small diameter alone normally prevents collapse. However, bronchioles have a proportionately thicker layer of smooth muscles than bronchi. Contraction of this smooth muscle narrows the bronchiole diameter and decreases the amount of air passing through the bronchial tree. The nose, larynx, trachea, and bronchi are supported by cartilage.

13. The nose, larynx, trachea, and bronchi are respiratory structures that are supported by cartilage. (Bronchioles and alveolar sacs are not.)

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14. Nasal hairs keep large pathogens and debris out of the nasal cavity. Mucus traps pathogens and particulates, and also humidifies inspired air. Tonsils (which are composed of lymphatic tissue in the pharynx) and macrophages (within the respiratory zone) destroy pathogens. Cilia continuously sweep mucus (and particulate matter that is trapped in it) inferiorly in the nasal cavity and pharynx and superiorly in lower respiratory tract so that it may be expectorated or swallowed. Sneezing and coughing reflexes produce bursts of air that expel substances from the respiratory system.

15. Air will pass through the nose, nasal cavity, nasopharynx, oropharynx, laryngopharynx, larynx, trachea, main bronchi, lobar bronchi, segmental bronchi, bronchioles including the terminal bronchioles and respiratory bronchioles, alveolar ducts, and alveoli.

16. Oxygen will pass through the alveolar epithelium, then through the fused basement membranes of the alveolar epithelium and the capillary endothelium, and finally the capillary endothelium.

17. The matched components of the lung with their air passageways are: main bronchus and lung, lobar bronchus and lobe, segmental bronchus and bronchopulmonary segment, terminal bronchiole and lobule.

18. Bronchial arteries provide the tissues of the lung with oxygenated blood, and bronchial veins drain the tissues of the lungs of deoxygenated blood. Some of the deoxygenated blood from the bronchial veins drains into the oxygenated blood within the pulmonary veins. (Thus, blood returned to the left side of the heart via pulmonary veins is slightly less oxygenated than the blood that left the lungs.)

19. Serous fluid acts as a lubricant, ensuring the pleural surfaces slide by each other with minimal friction during breathing.

20. The pressure in the pleural cavity, called the intrapleural pressure, is lower than the pressure inside the lungs, called the intrapulmonary pressure. It occurs because of the contrasting outward pull of the chest wall and the opposing inward pull of the lungs due to the lungs elastic tissue. This causes a vacuum or “suction” within the pleural cavity. The greater intrapulmonary pressure keeps the lungs inflated and prevents collapse of the lung.

21. Autonomic nuclei in the brainstem stimulate the skeletal muscles involved with breathing to rhythmically contract and relax, resulting in thoracic cavity volume changes. Dimensional changes within the thoracic cavity during breathing result in pressure changes, establishing a changing pressure gradient between the lungs and the atmosphere. Air moves down the pressure gradient either to enter the lungs during inspiration or to exit the lungs during expiration.

22. 1) The diaphragm contracts, increasing thoracic cavity vertical dimensions, and external intercostal muscles contract, increasing both lateral and anterior-posterior dimensions. This results in an increase in the volume of the pleural cavity, and an accompanying decrease in intrapleural pressure. 2) The lungs expand because of the surface tension caused by serous fluid in the pleural cavity, and intrapulmonary pressure decreases as the alveolar volume increases. 3) When the intrapulmonary pressure decreases below atmospheric pressure, air moves into the lungs.

23. Forced inspiration and expiration involve steps similar to quiet breathing; however, they are both active processes that require the recruitment of additional muscles. Their activity causes greater changes in both the thoracic cavity volume and intrapulmonary pressure; thus, more air moves into and out of the lungs and more energy is expended during forced breathing.

24. The ventral respiratory group (VRG) initiates nerve signals for inspiration and expiration. The dorsal respiratory group (DRG) receives sensory input from receptors and from other brain regions and then relays these nerve signals to the VRG, which causes a change in the rate and depth of breathing.

25. An increase in blood PCO2 and an increase in blood H+ (in either the blood or CSF) will increase the respiratory rate.

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26. Skeletal muscles of breathing are innervated by the somatic nervous system. However, the control of the breathing muscles comes from both autonomic nuclei in the brainstem, as well as somatic nuclei in the cerebral cortex. The autonomic nuclei in the respiratory center regulate normal breathing with their rhythmic motor output along the lower motor neurons of the phrenic and intercostal nerves. The cerebral cortex regulates breathing by directly stimulating lower motor neurons that extend to the skeletal muscles of breathing. This provides the means of controlling breathing both reflexively and consciously.

27. Resistance to airflow may be caused by 1) a decrease in elasticity of the chest wall and lungs, 2) a decrease in the bronchial diameter or the size of the passageway through which air moves, or 3) the collapse of alveoli. In order to overcome this resistance, the muscles of inspiration must work harder, and a greater amount of the body’s metabolic energy must be spent on breathing.

28. Long, deep breaths would provide greater alveolar ventilation. Two breaths require you to overcome the dead air space twice, whereas one long, deep breath provides the opportunity for gas exchange, similar to two quick breaths, but only has to contend with the dead air space once.

29. Respiratory capacities are calculated by adding together of two or more respiratory volumes. 1) The inspiratory capacity (IC) is the sum of the tidal volume and the inspiratory reserve volume. 2) The functional residual volume capacity (FRC) is the sum of the expiratory reserve volume plus the residual volume. 3) Vital capacity (VC) is the sum of the tidal volume plus both the inspiratory reserve volume and expiratory reserve volume. 4) Total lung capacity (TLC) is the sum of all the volumes, including the residual volume, and is the maximum volume of air that the lungs can hold.

30. Henry’s Law states that at a given temperature, the solubility of a gas in a liquid is dependent upon 1) the partial pressure of the gas in the air and 2) the solubility coefficient of the gas in the liquid. Carbon dioxide has a solubility coefficient 24 times greater than oxygen; therefore, at the same partial pressure, carbon dioxide would be far more soluble than oxygen.

31. During alveolar gas exchange, oxygen will diffuse into the blood (within the pulmonary capillaries) from the alveoli until the partial pressure of oxygen reaches equilibrium at 104 mm Hg. Carbon dioxide will diffuse out of the blood (within the pulmonary capillaries) into the alveoli, until the partial pressure of carbon dioxide reaches equilibrium at 40 mm Hg. 32. Loss of alveoli (which decreases the surface area of the respiratory membrane), fluid accumulation in the lungs (which increases the distances the respiratory gases must diffuse across the respiratory membrane), or arteriole vasoconstriction (which allows less blood to enter the pulmonary capillaries) will decrease alveolar gas exchange. In comparison, bronchiole dilation (which allows more air to enter alveoli) will increase alveolar gas exchange.

33. During systemic gas exchange, oxygen will diffuse from the blood (within the systemic capillaries) into systemic cells until the partial pressure of oxygen reaches equilibrium at 40 mm Hg. Carbon dioxide will diffuse out of the systemic cells into the blood (within the systemic capillaries) until the partial pressure of carbon dioxide reaches equilibrium at 45 mm Hg. 34. The solubility of oxygen in blood plasma is very low so only small amounts are dissolved in plasma.

Most oxygen (98%) must be transported within erythrocytes where it attaches to the iron within hemoglobin, where it is called oxyhemoglobin.

35. The majority of carbon dioxide, approximately 70%, diffuses into erythrocytes and combines with water to form bicarbonate ions. The bicarbonate then diffuses into the plasma where it is transported to the lungs.

36. 1) During alveolar gas exchange, oxygen diffuses down its concentration gradient from alveoli into the blood.

2) Over 98% of the oxygen is transported as oxyhemoglobin, bound to iron hemoglobin; less than 2% of the oxygen is transported dissolved within blood plasma. 3) During systemic gas exchange oxygen diffuses from hemoglobin into the blood and then into tissues down its concentration gradient.

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37. 1) During systemic gas exchange carbon dioxide leaves tissue and enters the blood, down its concentration gradient. 2) About 23% of the carbon dioxide in the blood is transported bound to hemoglobin, as carbaminohemoglobin, while 7% of the carbon dioxide is transported dissolved in blood plasma. The majority of carbon dioxide (70%) is converted to bicarbonate (HCO3- and transported in plasma. 3) During alveolar gas exchange, carbon dioxide is regenerated from both carbaminohemoglobin and bicarbonate; and then it enters the alveoli from blood down the concentration gradient.

38. The affinity of hemoglobin for oxygen increases with increased PO2. Therefore, as the partial pressure of oxygen in the blood increases with alveolar gas exchange, so does the oxygen saturation of hemoglobin.

39. More oxygen is released from hemoglobin in response to decreased PO2 in systemic cells, increased temperature, increased H+ (decreased pH), increased levels of 2,3-BPG, or an increase in CO2.

40. During hyperventilation blood PO2 does not change (because hemoglobin is normally 98% saturated with oxygen); however, blood PCO2 decreases and resulting in hypocapnia.

41. During exercise blood PO2 and PCO2 levels stay relatively constant. This is because breathing depth changes to provide the additional oxygen required and to eliminate the additional carbon dioxide waste that is produced during cellular respiration.

42. Breathing during exercise may change due to 1) sensory signals relayed from proprioceptors in joints, muscles, and tendons in response to movement, 2) motor output originating in the cerebral cortex that initiates muscular movement during exercise, simultaneously relaying signals to the respiratory center, or 3) the conscious anticipation of participating in exercise.

Answers to “Do You Know the Basics?”

1. D Feedback: Respiration involves gas exchange within the respiratory system, muscle contraction for pulmonary ventilation, and regulation by the nervous system.

2. A Feedback: The lungs are divided lobes that consist of bronchopulmonary segments. These are composed of isolated lobules that are composed of the alveoli.

3. C Feedback: The intrapulmonary pressure is greater than the intrapleural pressure keeps the lungs inflated and prevents collapse of the lung.

4. A Feedback: Autonomic nuclei in the brainstem stimulate the skeletal muscles involved with breathing to contract and relax. The result is a change in thoracic cavity volume that produces a changing pressure gradient between the lungs and the atmosphere.

5. B Feedback: Quiet expiration does not involve muscle contraction.

6. C Feedback: The medulla oblongata contains ventral and dorsal respiratory groups. The pons contains the pontine respiratory center.

7. B Feedback: Carbon dioxide triggers chemoreceptors which adjust the respiratory rate.

8. C Feedback: Systemic gas exchange involves the movement of respiratory gases between blood and body tissues.

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9. C Feedback: The majority of carbon dioxide is carried in plasma as bicarbonate.

10. D Feedback: Upon release of oxygen, hemoglobin becomes less saturated.

11. Structurally, the respiratory tract is organized into an upper respiratory tract (which contains the nose, nasal cavity, and pharynx) and the lower respiratory tract (which includes the larynx, trachea, bronchi, bronchioles, alveolar ducts, and alveoli). Functionally, the respiratory tract is organized into the conducting zone (which serves as a conduit for air and includes all structures from the nose to the terminal bronchioles) and the respiratory zone (which allow for the exchange of respiratory gases and include the respiratory bronchioles, alveolar ducts, and alveoli).

12. The visceral pleura is a serous membrane that tightly adheres to the lung surface. The parietal pleura is a serous membrane that lines the internal thoracic wall, the lateral surface of the mediastinum, and the superior surface of the diaphragm. The pleural cavity is a potential space located between the visceral and parietal pleurae.

The serous fluid is an oily product of the serous membranes that acts as a lubricant, ensuring the pleural surfaces slide by each other with minimal friction during breathing. During pulmonary ventilation, the contrasting outward pull of the chest wall and the opposing inward pull of the lungs form a vacuum within the pleural cavity.

Consequently, the pressure generated in the pleural cavity, called the intrapleural pressure, is lower than the pressure inside the lungs, called the intrapulmonary pressure. This difference in pressure keeps the lungs inflated.

13. The four processes involved in moving oxygen from the atmosphere are 1) pulmonary ventilation, 2) alveolar gas exchange, 3) gas transport in the blood, and 4) systemic gas exchange. The four processes in transport of carbon dioxide from tissues to the atmosphere are 1) systemic gas exchange, 2) gas transport in the blood, 3) alveolar gas exchange, and 4) pulmonary ventilation.

14. For quiet inspiration, the diaphragm and external intercostal muscles contract; this increases the volume of the thoracic cavity with an accompanying decrease in the intrapulmonary pressure (and intrapleural pressure), resulting in air moving into the lungs. For quiet expiration, the diaphragm and external intercostals relax (and thoracic wall recoils); this decreases the volume of the thoracic cavity with an accompanying increase in the intrapulmonary pressure (and intrapleural pressure), resulting in air moving out of the lungs.

15. Forced breathing involves steps similar to quiet breathing. However, both forced inspiration and expiration are active processes, requiring contraction of additional muscles. Their activity causes greater changes in both the thoracic cavity volume and intrapulmonary pressure. Consequently, more air moves into and out of the lungs.

16. Neurons in the ventral respiratory group (VRG) of the medullary respiratory center spontaneously depolarize, initiating nerve signals for inspiration. Nerve signals are relayed via both the phrenic nerves (to the diaphragm) and intercostal nerves (to the intercostal muscles). Inspiratory neuron stimulation causes both the diaphragm and external intercostal muscles to contract, resulting in an increase in thoracic cavity volume. Ultimately, inspiratory neurons are inhibited by expiratory neurons of the ventral respiratory group and the pontine respiratory group.

Inspiratory impulses cease. Lack of nerve stimulation causes both the diaphragm and external intercostal muscles to relax, and then thoracic cavity volume decreases. The cycle is then repeated about 12 to 15 times per minute.

17. During alveolar gas exchange oxygen enters the blood because the partial pressure of oxygen is greater within alveoli than in blood. Carbon dioxide leaves the blood because its partial pressure is greater in blood than in alveolar air. During systemic gas exchange oxygen leaves the blood because its partial pressure is greater in the blood than in the tissue. Conversely, carbon dioxide leaves the tissue where its partial pressure is higher and enters the blood where its partial pressure is lower.

18. Over 98% of the oxygen is transported as oxyhemoglobin, attached to iron within hemoglobin; less than 2% of the oxygen is dissolved in blood plasma. Carbon dioxide has three means of transport: 1) 23% of the carbon dioxide in the blood is transported bound to hemoglobin, as carbaminohemoglobin; 2) 7% of the carbon dioxide is

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transported dissolved in blood plasma; and 3) the majority of carbon dioxide (nearly 70%) is converted to carbonic acid by carbonic anhydrase (this spontaneously dissociates into bicarbonate ions and H+ which are readily dissolved in the blood).

19. The affinity of hemoglobin for oxygen increases with increased PO2. The binding of each O2 molecule causes a conformation change in hemoglobin that makes it progressively easier for each additional O2 molecule to bind to an available iron.

20. Increased temperature, increased concentrations of H+, presence of 2,3-BPG, or increased CO2 binding to globin all decrease the affinity of hemoglobin for oxygen. This decrease in affinity results in additional oxygen being released during systemic gas exchange.

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: The pons adjust the activity of the ventral respiratory group of the medulla oblongata.

2. D Feedback: Emphysema results from the loss of alveolar surface area.

3. C Feedback: Decreased capacity to ventilate her lungs will require her to engage accessory muscles to ventilate her lungs, thereby expending more energy.

4. A Feedback: Poor ventilation and gas exchange will result in lowered blood PO2, and increased PCO2. The increased PCO2 causes formation of H+ (and a decrease in pH).

5. B Feedback: Asthma is usually an allergic reaction, leading to inflammation of mucous membranes and bronchoconstriction of bronchioles, which greatly decreases the amount of air able to reach the respiratory zone.

Answers to “Can You Synthesize What You’ve Learned?”

1. Asthma is usually an allergic reaction leading to inflammation of mucous membranes and bronchoconstriction of bronchioles, greatly decreasing the amount of air able to reach the respiratory zone. This would result in lowered blood PO2, and increased PCO2. The primary treatment for asthma consists of administering inhaled steroids to reduce the inflammatory reaction, combined with bronchodilators to alleviate the bronchoconstriction.

2. The sternocleidomastoid participates in expansion of the lungs during forced inspiration.

3. As altitude increases, the PO2 of air decreases, and subsequently alveolar PO2 is lowered. Since the alveolar exchange of oxygen is driven by the PO2 gradient between alveoli and the blood, less O2 will enter the blood, resulting in poor hemoglobin saturation. In response to the drop in blood PO2 the rate of pulmonary ventilation would increase, decreasing blood PCO2, possibly decreasing blood pH, which would cause respiratory alkalosis.

Decreased PO2 also causes vasoconstriction of blood vessels in the brain, depriving the brain of oxygen, which can cause dizziness and fainting.

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Chapter 24 Answers to “What Did You Learn?”

1. The kidneys form urine. The urinary bladder stores urine.

2. The kidneys help regulate blood pressure by 1) excreting fluid in the urine to help regulate blood volume, and 2) releasing the enzyme renin, which is required for production of angiotensin II, a hormone that increases blood pressure.

3. The fibrous capsule (also called renal capsule) is composed of dense irregular connective tissue. It functions to maintain the kidney’s shape, protects it from trauma, and helps prevent infectious pathogens from penetrating the kidney.

4. A space called the renal sinus serves as the urine drainage area. It is organized into minor calyces, major calyces, and a renal pelvis.

5. The sympathetic division of the autonomic system innervates the afferent arterioles, the efferent arterioles, and each juxtaglomerular apparatus within the kidneys.

6. The renal corpuscle consists of 1) a glomerulus which is thick tangle of capillary loops, and 2) a glomerular capsule which is formed by two cell layers: an internal, permeable visceral layer that overlies the glomerular capillaries and an external, impermeable parietal layer.

7. The renal tubule consists of three continuous sections: the proximal convoluted tubule, the nephron loop, and the distal convoluted tubule.

8. Cortical nephrons are oriented with their renal corpuscles near the peripheral edge of the cortex and have a relatively short nephron loop that barely penetrates the medulla. Juxtamedullary nephrons have a renal corpuscle adjacent to the corticomedullary junction, and they have relatively long nephron loops that extend deep into the medulla.

9. Principal cells respond to the hormones aldosterone (released from the adrenal cortex) and antidiuretic hormone (released from the posterior pituitary). Intercalated cells help regulate urine pH and blood pH by releasing varying amounts of hydrogen ions (H+) and bicarbonate ion (HCO3-).

10. The two primary cellular components of the juxtaglomerular apparatus are the granular cells and the macula densa cells. The granular cells are modified smooth muscle cells of the afferent arteriole located near its entrance into the renal corpuscle. They are stimulated either by stretch or innervation by the sympathetic division of the autonomic nervous system. The macula densa cells are a group of modified epithelial cells in the wall of the distal convoluted tubule where it contacts the granular cells. The detect changes in the sodium chloride (NaCl) concentrations of fluid within the distal convoluted tubule.

11. Blood flow pathway: the 1) renal artery, 2) segmental artery, 3) interlobar artery, 4) arcuate artery, 5) interlobular artery, 6) afferent arteriole, 7) glomerulus, 8) efferent arteriole, 9) either peritubular capillaries or vasa recta, 10) interlobular vein, 11) arcuate vein, 12) interlobar vein, and 13) renal vein.

12. The three major types of capillaries associated with the nephron are the 1) glomerulus, 2) peritubular capillaries, and 3) vasa recta. The glomerulus is a thick tangle of capillary loops within the renal corpuscle that is responsible for filtration of the blood. The peritubular capillaries are intertwined around both the proximal and distal convoluted tubules where they participate in reabsorption and secretion in most nephrons. The vasa recta are associated with the nephron loop and participate in exchange of gases, nutrients and wastes.

13. Fluid is called filtrate as it first passes through the 1) capsular space; then it is called tubular fluid as it passes through the 2) proximal convoluted tubule, 3) descending limb of the nephron loop, 4) ascending limb of the

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nephron loop, 5) distal convoluted tubule, 6) collecting tubules, and 7) collecting duct. After this point, it is referred to as urine, which continues to move through the 8) papillary duct, 9) minor calyx, 10) major calyx, 11) renal pelvis, 12) ureter, 13) urinary bladder, and finally 14) the urethra.

14. Tubular reabsorption occurs when components within the tubular fluid move by diffusion, osmosis, or active transport from the lumen of the renal tubules, collecting tubules, and collecting ducts across their walls and return to the blood within the peritubular capillaries and vasa recta. Tubular secretion is the movement of solutes, usually by active transport out of the blood within the peritubular and vasa recta capillaries into the tubular fluid.

15. The filtration membrane of the glomerulus from innermost (closest to the lumen) to outermost is: 1) endothelium (fenestrated) of the glomerulus, 2) basement membrane of the glomerulus, and 3) visceral layer of the glomerular capsule (composed of specialized cells called podocytes).

16. Small substances such as water, glucose, amino acids, ions, some hormones, water soluble vitamins B and C, and ketones can pass easily through the filtration membrane. Formed elements (like erythrocytes, leukocytes, and platelets) and large proteins are structures that cannot normally pass through the filtration membrane.

17. Kidney trauma caused by exposure to heavy metals and/or some bacterial toxins may result in increased permeability of the filtration membrane and permit protein (and perhaps formed elements) to enter the filtrate.

18.

NFP = HPg – (OPg + HPc) NFP = 65 mm Hg – (30 mm Hg + 20 mm Hg) NFP = 15 mm Hg

19.

The net filtration pressure would increase, since: NFP = HPg – (OPg + HPc) NFP = 75 mm Hg – (30 mm Hg + 20 mm Hg) NFP = 25 mm Hg

20. If HPg increases the net filtration pressure increases. There is a direct relationship between the net filtration pressure and glomerular hydrostatic (blood) pressure.

21. Urine production increases with an increase in the glomerular filtration rate.

22. Renal autoregulation maintains GFR by altering the size of the afferent arteriole in response to changes in systemic blood pressure. Stimulation by the sympathetic division decreases GFR. Direct stimulation by the sympathetic division of the autonomic nervous system causes 1) vasoconstriction of afferent arterioles and 2) renin release with the subsequent production of angiotensin II and contraction of mesangial cells that decrease the surface area of the glomerulus. Atrial natriuretic peptide increases GFR through vasodilation of the afferent arteriole, inhibition of renin release, and the subsequent relaxation of mesangial cells that increase the surface area of the glomerulus.

23. A person with blood pressure of 300/150 mm Hg would have a mean arterial pressure of 200 mm Hg. A person with blood pressure of 70/55 mm Hg would have a mean arterial pressure of 60 mm Hg. Both values are outside of the range manageable through renal autoregulation.

24. In order to be reabsorbed or secreted, substances must be able to move across the simple epithelium of the renal tubule, either by paracellular or transcellular transport. During transcellular transport, a substance must cross two separate plasma membranes, a luminal membrane and a basolateral membrane, and the appropriate transport proteins must be present in sufficient quantities to support this transport. Finally, peritubular capillaries

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have both low hydrostatic pressure and high colloid (oncotic) pressure for reabsorption of substances into peritubular capillaries.

25. The transport maximum is the maximum rate that a substance that can be reabsorbed (or secreted) across the tubule epithelium (i.e., amount per time). This is dependent upon the number of the transport proteins in the epithelial cell membrane specific for the substance. This is different from the renal threshold, which is the maximum plasma concentration of a substance that can be carried in the blood without eventually appearing in the urine (i.e., amount per volume of plasma).

26. Glucose concentration is relatively high inside the tubule cell and relatively low within both the tubule lumen and interstitial fluid. Glucose is first transported into the tubule cell across the luminal membrane by a Na+/glucose symporter. Energy from Na+ moving down its concentration gradient into the tubule cell is used to move glucose up its concentration gradient into the tubule cell by secondary active transport. Glucose is then moved by glucose uniporters out of the tubule cell down its concentration gradient via facilitated diffusion across the basolateral membrane.

27. Proteins undergo transformational changes while being reabsorbed. The proteins are a) either taken up into the tubule cells and then digested into their amino acid building blocks by lysosomes in the renal tubule cells or b) first digested into amino acids by peptidases that are embedded in the luminal membrane and then the amino acids are taken up into the tubule cells. These amino acids are then moved by facilitated diffusion across the basolateral membrane into the blood.

28. Sodium reabsorption occurs along the entire length of the renal tubule. An Na+/K+ pump moves sodium out of tubular cells, into the interstitial space, forming a Na+ gradient. Since the sodium concentration is greater in tubular fluid than within the tubular cells, it will diffuse down the gradient into tubular cells, and then out through the basolateral membrane into the interstitial fluid. Aldosterone will increase reabsorption of sodium by increasing the number of sodium channels and Na+/K+ pumps available to the tubular cell. Atrial natriuretic peptide inhibits both the release of aldosterone and the reabsorption of Na+.

29. Parathyroid hormone inhibits PO43- reabsorption in the proximal convoluted tubule and stimulates reabsorption of Ca2+ in the distal convoluted tubule.

30. Type A intercalated cells secrete H+ into the tubular fluid and reabsorb HCO3- to raise blood pH (more alkaline) and decrease urine pH (more acidic). Conversely, type B intercalated cells secrete HCO3- and reabsorb H+ to lower blood pH and increase urine pH. 31. The kidneys eliminate nitrogenous wastes (such as urea, uric acid, and creatinine), certain drugs (antibiotics including penicillin and sulfonamides, and aspirin), urobilin (a bilirubin breakdown product), hormone metabolites, human chorionic gonadotropin (hCG), epinephrine, and prostaglandins.

32. The countercurrent multiplier system along the nephron loop establishes a salt gradient necessary to drive the reabsorption of water. The descending limb of the loop is permeable to water, but not to salt. The ascending limb is impermeable to water, but actively pumps salt out of the loop into the interstitial fluid. Consider that as the salt concentration in the interstitial fluid increases 1) an even greater amount of water moves out of the descending limb and 2) this increases the salt concentration in the tubular fluid that flows into the ascending limb, which 3) allows even more salts to be pumped out of the ascending limb. Consequently, the concentration of salts in the interstitial fluid is increased or “multiplied” through this positive feedback loop.

The countercurrent exchange process involving the vasa recta helps to maintain a salt gradient. As the blood flows through the vasa recta deep into the renal medulla alongside the ascending limb, water moves by osmosis out of these capillaries into the more concentrated interstitial fluid. At the same time, salts in the interstitial fluid enter the vasa recta by diffusion down their concentration gradients. Thus, the blood in the vasa recta is losing water and gaining salts, and the concentration of total salt in the blood increases. Thus, as blood within the vasa recta travels into the deepest part of the medulla, it becomes more and more concentrated. If the vasa recta were to continue deep into the medulla, these salts would be transported away in the blood. However, the path of the blood flow in the vasa recta makes a 180-degree turn and is positioned alongside the descending limb of the

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nephron loop toward the cortex. Salts are now transported into a region in which osmotic and solute gradients reverse. Here, the salts diffuse back out of the blood into the interstitial fluid, while water moves into the vasa recta. Thus, as blood within the vasa recta travels toward the cortex, it becomes less and less concentrated. Most importantly, it leaves the salts responsible for the concentration gradient in the interstitial fluid.

An important and additional contribution to maintaining the concentration gradient in the interstitial fluid occurs with urea recycling. Recycled urea in fact makes up approximately one-half of the solutes of the interstitial fluid concentration gradient. Urea is removed from the tubular fluid in the collecting duct by urea uniporters as mentioned previously; it diffuses back into the tubular fluid in the thin segment of the ascending limb. Because both the thick segment of the ascending limb and DCT are not permeable to urea, urea remains within the tubular fluid until it reaches the collecting duct, where it is removed from the tubular fluid. Thus, urea is “cycled” between the collecting tubule and nephron loop. Some of this urea remains in the interstitial fluid, contributing to its concentration gradient.

33. The proximal convoluted tubule reabsorbs 100% of nutrients and most of the water and ions. It also secretes some drugs and nitrogenous waste products. The nephron loop reabsorbs water. The distal convoluted tubule reabsorbs sodium, water, potassium, calcium, bicarbonate, and protons. The collecting duct is responsible for the reabsorption of urea.

34. The glomerular filtration rate is an indicator of renal function.

35. It is important to determine renal plasma clearance to know the amount and timing of drug dosage. The higher the renal plasma clearance, the more often the medications must be given to maintain therapeutic levels.

36. Urine characteristics include its composition, volume, pH, specific gravity, color and turbidity, and smell.

The pH of urine may be affected by diet, metabolism, or bacterial infections.

37. The urinary tract consists of the ureters (long, epithelial-lined, fibromuscular tubes that conduct urine from the kidneys to the urinary bladder), the urinary bladder (an expandable, muscular container that serves as a reservoir for urine), and the urethra (an epithelial lined fibromuscular tube that conducts urine to the exterior of the body). The 1) ureters consist of a mucosa, muscularis, and adventitia; the 2) urinary bladder consists of a mucosa, submucosa, muscularis, and adventitia; and the 3) urethra is lined by a protective mucous membrane that houses urethral glands (clusters of mucin-producing cells), surrounded by bundles of smooth muscle fibers that help propel urine to the outside of the body.

38. The male and female urethras differ in both length and morphology. The female urethra has a single function: to transport urine from the urinary bladder to the exterior of the body. The entire length of the female urethra is lined with stratified squamous epithelium. The male urethra is longer and has both urinary and reproductive functions. In the male, the prostatic urethra extends through the prostate gland immediately inferior to the male bladder. It is lined with transitional epithelium. The membranous urethra is the shortest portion of the male urethra and extends from the inferior surface of the prostate gland through the urogenital diaphragm. The epithelium here is often either stratified columnar or pseudostratified columnar. The spongy urethra is the longest part of the male urethra and is encased within a cylinder of erectile tissue in the penis called the corpus spongiosum. The proximal part of the spongy urethra is lined by a pseudostratified columnar epithelium; the distal part has a stratified squamous epithelium.

39. 1) Distention of the bladder wall (usually at about 200-300 mL of urine) triggers baroreceptors. (2) Baroreceptors send nerve signals along sensory neurons to the micturition reflex center within the pons. (3) The micturition center alters nerve signals propagated down the spinal cord and through pelvic splanchnic nerves (parasympathetic nerves). (4) Parasympathetic stimulation causes smooth muscle cells of the detrusor muscle to contract and the internal urethral sphincter to relax. The conscious decision to urinate is due to altering nerve signals relayed from the cerebral cortex through the spinal cord and along the pudendal nerve to cause relaxation of the external urethral sphincter. Voluntary relaxation of the external urethral sphincter along with Valsalva maneuver allows micturition. Urination may occur without conscious control once the bladder contains 500–600 mL of urine.

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Answers to “Do You Know the Basics?”

1. D Feedback: The kidneys do not produce plasma proteins. Most plasma proteins are produced by the liver.

2. B Feedback: The kidneys are located posterior to the peritoneum within the abdominal cavity.

3. A Feedback: Collecting ducts and nephron loops are present in the renal medulla.

4. B Feedback: The minor calyx is a funnel-shaped urine drainage area associated with a renal pyramid.

5. D Feedback: Under normal conditions, 100% of glucose is reabsorbed in the proximal convoluted tubule.

6. C Feedback: There is a direct relationship between glomerular filtration and urine production. Increased glomerular filtration causes increased urine production.

7. D Feedback: Aldosterone increases sodium reabsorption, which is directly related to water reabsorption and inversely related to potassium reabsorption.

8. C Feedback: If the concentration of a substance exceeds the maximum capacity for its reabsorption, it will eventually appear in the urine.

9. C Feedback: The nephron loop establishes the salt concentration gradient within the renal medulla through the countercurrent multiplier system (assisted by the countercurrent multiplier associated with the vasa recta and urea cycling).

10. C Feedback: ADH stimulates the reabsorption of water from tubular fluid, decreasing urine volume, and increasing urine concentration.

11. Blood flow pathway: the 1) renal artery, 2) segmental artery, 3) interlobar artery, 4) arcuate artery, 5) interlobular artery, 6) afferent arteriole, 7) glomerulus, 8) efferent arteriole, 9) either peritubular capillaries or vasa recta, 10) interlobular vein, 11) arcuate vein, 12) interlobar vein, and 13) renal vein.

12. Filtrate is present in the capsular space. It is referred to as tubular fluid in the proximal convoluted tubule, nephron loop, distal convoluted tubule, collecting tubule, and collecting duct. Tubular fluid has no further changes made to it after leaving the collecting ducts. It is then called urine and it enters a papillary duct before flowing progressively through spaces in the renal sinus (minor calyx, major calyx, renal pelvis). Thereafter it leaves the kidney and enters into a ureter.

13. The primary components of the juxtaglomerular apparatus are the granular cells and the macula densa.

Granular cells are modified smooth muscle cells of the afferent arteriole located near its entrance into the renal corpuscle. The macula densa is a group of modified epithelial cells in the wall of the distal convoluted tubule where it contacts the granular cells. The cells of the macula densa are located only on the tubule side next to the afferent arteriole, and they are narrower and taller than other distal convoluted tubule epithelial cells.

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15. The filtration membrane is composed of three layers: 1) Endothelium of the glomerulus—it is fenestrated.

2) Basement membrane of the glomerulus—it is porous and composed of glycoproteins and proteoglycans.

3) Visceral layer of glomerular capsule - it is composed of specialized cells called podocytes, which have long, foot-like processes (pedicels) that wrap around the glomerular capillaries to support the capillary wall but do not completely ensheathe it. Plasma and dissolved substances are filtered; however, the passage of large structures such as formed elements and plasma proteins is prevented.

16. The Glomerular Filtration Rate (GFR) is regulated by several processes. 1) Renal autoregulation is the intrinsic ability of the kidney to maintain a constant blood pressure and glomerular filtration rate by altering the size of the afferent arteriole in response to changes in systemic blood pressure. If systemic blood pressure increases, the smooth muscle within the afferent arteriole wall contracts, and may be stimulated to further contract by the tubuloglomerular feedback mechanism. (This occurs when the macula densa cells detect an increase in NaCl, which is an indirect measure of increased blood pressure in the glomerulus; these cells release chemicals that cause smooth muscle in the afferent arteriole wall to contract to a greater extent.) This allows less blood into the glomerulus to offset the increase in blood pressure. If systemic blood pressure decreases, the smooth muscle within the afferent arteriole wall relaxes, allowing an additional amount of blood to enter the glomerulus to offset the decrease in blood pressure. 2) Activation of the sympathetic division of the autonomic nervous system causes vasoconstriction of the afferent arteriole and a decrease in the surface area of the filtration membrane. This decreases GFR and urine formation. 3) Atrial natriuretic peptide increases GFR through vasodilation of the afferent arteriole, inhibition of renin release, and the subsequent relaxation of mesangial cells to increase filtration membrane surface area.

17. Aldosterone induces principal cells to synthesize both Na+ channels and Na+/K+ pumps, which increases the reabsorption of Na+ from tubular fluid. Water follows the Na+ and urine volume will decrease. (K+ is exchanged with Na+ by the Na+/K+ pump and this K+ is then secreted into the tubular fluid and excreted in urine. Thus, aldosterone functions to retain both Na+ and water and eliminate K+.)

Antidiuretic hormone (ADH) increases water reabsorption from the filtrate by increasing migration of vesicles containing aquaporins to the membranes of principal cells, facilitating increased water reabsorption, and a subsequent smaller volume of more concentrated urine.

18. Antidiuretic hormone (ADH) increases water reabsorption from the filtrate by increasing migration of vesicles containing aquaporins to the membranes of principal cells. However, it is the concentration gradient in the medulla that serves as the osmotic pull to move water from the tubular fluid across the luminal membrane and basolateral membrane into the interstitial fluid. Water then moves from the interstitial fluid into the blood within the vasa recta.

19. Blood plasma contains formed elements, proteins, nutrients, salts, and waste products. Filtrate usually lacks formed elements and only very small amount of proteins. Urine lacks both nutrients (e.g., glucose) and the small amount of protein that might have been filtered. On average 1 ½ liters of urine are produced daily, which contains water with dissolved ions, some hormones, metabolic wastes (e.g., urea, uric acid, creatinine) and perhaps some medications.

20. Kidney functions include: a) maintaining blood pH, b) regulating blood ion concentrations, c) regulating blood volume and blood pressure, d) eliminating wastes, some hormones, and certain drugs from the blood, e) releasing renin, f) releasing erythropoietin, and g) stimulating the final step in calcitriol formation.

21. The expulsion of urine from the bladder is called micturition. 1) As the volume of urine produced increases, the distention of the bladder wall triggers baroreceptors. 2) Baroreceptors stimulate the micturition reflex center within the pons. 3) The micturition center stimulates parasympathetic nerves to the bladder. 4) Parasympathetic stimulation causes smooth muscle cells of the detrusor muscle to contract and the internal urethral sphincter to relax. The conscious decision to urinate is due to altering nerve signals relayed from the cerebral cortex through the spinal cord and along the pudendal nerve to cause relaxation of the external urethral sphincter. Voluntary relaxation of the external urethral sphincter along with Valsalva maneuver allows micturition. Urination may occur without conscious control once the bladder contains 500–600 mL of urine.

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Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: Her elevated blood pressure (hypertension) will increase glomerular filtration resulting in protein loss in the urine.

2. C Feedback: Plasma protein levels will decrease as they are lost in urine.

3. B Feedback: Excess protein in tubular fluid will create an osmotic pressure gradient that counteracts water reabsorption, resulting in decreased water reabsorption, and increased urine production.

4. A Feedback: Glomerular blood pressure is directly related to systemic blood pressure. As systemic blood pressure drops, so does the GFR. A drop in GFR will cause a drop in urine production.

5. D Feedback: Severing the spinal cord will not affect the reflexive mechanisms of emptying the bladder upon distention. It will inhibit conscious control over micturition because nerve signals from his cerebral cortex can no longer be transmitted to the bladder. Therefore, incontinence will result.

Answers to “Can You Synthesize What You’ve Learned?”

1. High renal clearance means that the drug is removed quickly from the patient’s bloodstream. It will need to be administered more often.

2. Atrial natriuretic peptide increases glomerular filtration rate (GFR). It also inhibits both the reabsorption of Na+ in the proximal convoluted tubule and collecting tubules as well as the release of aldosterone.

Consequently, more Na+ and water are excreted in urine, reducing blood volume.

3. The prostatic urethra passes through the prostate gland. Enlargement of the prostate gland will put pressure on the urethra, occluding it and preventing micturition.

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Chapter 25 Answers to “What Did You Learn?”

1. An increase in muscle mass due to weight training will result in an increase in percentage of body fluid since skeletal muscle tissue is approximately 75% water.

2. Potassium cations, magnesium cations, and phosphate anions are more prevalent in intracellular fluid.

Sodium cations, calcium cations, bicarbonate anions, and chloride anions are more prevalent in extracellular fluid.

3. The major difference between the composition of blood plasma and interstitial fluid is that protein is present in blood plasma, but very little protein is found within the interstitial fluid.

4. When you are dehydrated, the net movement of water is from cells into the blood plasma.

5. Preformed water from absorbed food and drink in the diet and metabolic water from cellular respiration and dehydration reactions comprise the total water intake.

Fluid output is fluid lost from the body, which includes loss through breathing, sweating, cutaneous transpiration, defecation, and urination. Fluid output is categorized as a) sensible or insensible (depending upon if it is measureable) and b) obligatory or facultative (depending on if it is regulated based on the hydrated state of the body). Urine production (beyond ½ liter) is dependent upon the hydrated state of the body and is the only physiologic mechanism to control fluid output by hormonal regulation.

6. Fluid deficiency is loss of isotonic body fluid, which does not change the osmolarity; thus, there is no net movement of fluid between fluid compartments. In comparison, dehydration is a loss of greater amounts of water than the loss of solutes, thus blood plasma becomes hypertonic (so there is a change in osmolarity).

Consequently, water shifts between fluid compartments with a net movement of water from the cells into the plasma.

7. The stimuli that activate the thirst center are: decreased salivary secretions, increased blood osmolarity, and decreased blood pressure. These stimulate an increase in thirst.

8. Atrial natriuretic peptide increases urine output to decrease both blood volume and blood pressure.

9. Electrolytes can dissociate into constituent ions. Osmotic pressure is dependent upon the number of solutes in a solution; therefore, electrolytes contribute more to the osmotic pressure.

10. Decreased pH will cause a net efflux of potassium ions from cells. When H+ increases (pH decreases) in the extracellular fluid, excess H+ moves from the extracellular fluid into the intracellular fluid to reestablish acidbase balance. At the same time, K+ moves in the opposite direction, from the intracellular fluid into the extracellular fluid, to prevent the development of an electrostatic gradient.

11. Angiotensin II increases glomerular filtration rate (GFR) by stimulating vasoconstriction of afferent arterioles (i.e., less inflow into the glomerulus) and contraction of the mesangial cells within the glomerulus (decreasing filtration membrane surface area). Decreased GFR leads to decreased urine production.

Angiotensin II stimulates the thirst center in the hypothalamus, inducing the uptake of water.

Angiotensin II also induces the release of both aldosterone from the adrenal cortex, facilitating the retention of sodium in the kidneys and, subsequently, the retention of water and the release of antidiuretic hormone, which increases water reabsorption. Both processes decrease urine output.

12. The release of ADH from the hypothalamus is stimulated by a) angiotensin II (which was previously produced in response to low blood pressure), b) a decrease in sensory input from baroreceptors within the atria of the heart and aorta and carotid blood vessels, which are stimulated by decrease in stretch in response to low blood volume, and c) an increase in blood osmolarity, which is detected by chemoreceptors within the hypothalamus. Thus, ADH is released in response to low blood pressure, low blood volume, and increased blood osmolarity.

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ADH stimulates these effectors: 1) the thirst center in the hypothalamus, which potentially results in fluid intake, increasing both blood volume and blood pressure and decreasing blood osmolarity; 2) the kidneys, to increase the number of aquaporins in collecting tubules and collecting ducts, in turn increasing water reabsorption, which decreases urine output to help maintain blood volume; and, in high doses 3) smooth muscle within walls of systemic blood vessels, causing vasoconstriction and increasing peripheral resistance, which results in an increase in systemic blood pressure.

13. Aldosterone increases the number of Na+/K+ pumps and Na+ channels in principal cells of the kidney.

More Na+ is reabsorbed from the filtrate back into the blood. Water follows the Na+ movement by osmosis.

Fluid retention results in decreased urine output. K+ is secreted (and then excreted).

However, in conditions of low pH, as Na+ and water are reabsorbed from the tubule into the blood, H+ (instead of K+) is secreted from the blood into the tubule. The loss of excess H+ assists in returning blood pH to within normal homeostatic limits.

14. ANP decreases both blood volume and blood pressure by causing the following responses: 1) vasodilation to decrease peripheral resistance and decrease blood pressure, 2) increased glomerular filtration rate (GFR) to increase urine output and decrease blood volume and blood pressure, 3) increased loss of Na+ and water in urine to decrease blood volume and blood pressure, 4) inhibition of the release of renin, the action of angiotensin II, and the release of ADH and aldosterone.

15. The acid-base balance is the regulation of hydrogen ion concentration in body fluids in order to maintain an arterial blood pH between 7.35 and 7.45. It is also called pH balance.

16. Fixed acids (also called metabolic acids) are wastes produced from metabolic processes other than that produced from carbon dioxide. These include, for example, lactic acid from glycolysis, phosphoric acid from nucleic acid metabolism, and ketoacids from fatty acid metabolism. Volatile acid is carbonic acid produced when carbon dioxide combines with water.

17. The kidneys respond to fixed acids (metabolic acids) by reabsorbing all filtered HCO3- along the length of the nephron, synthesizing and absorbing new HCO3-, and excreting H+ into the filtrate. The process is relatively slow, taking from several hours to days.

18. During hyperventilation, blood CO2 levels decrease, causing the H+ concentration in the blood to decrease, which increases the pH. 19. The three chemical buffering systems are the protein buffering system, the phosphate buffering system, and the bicarbonate buffering system. 1) The protein buffering system buffers within cells and in blood plasma. 2) The phosphate buffering system buffers within the intracellular fluid. 3) The bicarbonate buffer system buffers within the blood.

20. The chemical buffering system is quick to respond (within seconds); however, it has a limited buffering capacity. Under normal conditions, chemical buffers provide adequate buffering, until the respiratory system is able to adjust conditions accordingly (within minutes). The urinary system provides long-term buffering (hours or days), especially for metabolic acids.

21. The response of physiologic buffering systems to acid-base disturbances that results in the return of blood pH to normal is called compensation. An uncompensated acid-base disturbance overwhelms the physiologic buffering systems to return the pH to normal (thus, the pH remains outside of the normal range of 7.35-7.45).

22. During hyperventilation, blood CO2 levels decrease due to rapid breathing, causing the H+ concentration in the blood to decrease and increasing the pH. 23. The most common cause of metabolic alkalosis is the loss of excessive amounts of H+ due to vomiting (or prolonged nasogastric suction).

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24. Renal compensation results in either elevated values for blood HCO3- (when attempting to compensate for acidosis) or decreased values for HCO3- (when attempting to compensate for alkalosis). Respiratory compensation can result in either elevated values for CO2 (when attempting to compensate for alkalosis) or lower values for CO2 (when attempting to compensate for acidosis).

Answers to “Do You Know the Basics?”

1. D Feedback: The percentage of body water increases with lean muscle mass.

2. A Feedback: Two thirds of body fluids are located within cells.

3. B Feedback: Increased blood hydrostatic pressure pushes fluid out of blood into the interstitial space during capillary exchange.

4. B Feedback: Decreased saliva production, increased blood osmotic pressure, decreased blood volume, and decreased blood pressure are symptoms of dehydration.

5. C Feedback: ANP decreases fluid output from the kidneys, thereby increasing blood volume and systemic blood pressure.

6. D Feedback: Electrolytes contribute to the osmolality of blood (because they dissociate in solution), and consequently affect the regulation of fluid balance.

7. C Feedback: Sodium ion is actively maintained at high concentrations within the ECF throughout the body in order to maintain osmotic pressure.

8. D Feedback: Carbon dioxide forms carbonic acid in blood, which disassociates into hydrogen ions and bicarbonate; thus, blood H+ levels increase, which decreases blood pH. 9. A Feedback: Carbohydrates do not serve as buffers.

10. D Feedback: The kidneys are capable of secreting or reabsorbing hydrogen ions, as well as producing bicarbonate in order to buffer blood.

11. The body’s fluid composition depends upon age and the relative amounts of adipose and skeletal muscle tissue.

12. When you drink water some of it will move from the gastrointestinal (GI) tract into the blood plasma. Plasma osmolarity decreases and blood plasma becomes hypotonic to the interstitial fluid and intercellular fluid. As blood moves through the capillaries, water first moves out of the blood plasma to become part of the interstitial fluid, and then moves from the interstitial fluid into the cells.

13. The stimuli that turn on the thirst center are decreased saliva production, increased blood osmolarity, and decreased blood pressure. The stimuli that turn off the thirst center are increased salivary production, distention of the stomach, decreased blood osmolarity, and increased blood pressure.

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14. Renin enzyme is released from granular cells (granular cells) of the juxtaglomerular apparatus into the blood in response to 1) low blood pressure or 2) stimulation by the sympathetic division. Renin converts angiotensinogen to angiotensin I, which is in turn converted by angiotensin converting enzyme (ACE) to its active form, angiotensin II. Angiotensin II increases systemic blood pressure by causing an increase in vasoconstriction, a decrease in fluid output, and an increase in blood volume (if fluid intake occurs). Increasing blood pressure is aided by the release of both ADH from the hypothalamus and aldosterone from the adrenal cortex. ADH and aldosterone increase water reabsorption in the kidney and aldosterone increases both sodium ion and water reabsorption in the kidney, which decreases urine output. A decrease in urine output helps maintain blood volume and blood pressure.

15. Atrial natriuretic peptide (ANP) is released in response to increased stretch in atria as a consequence of high blood volume and high blood pressure. ANP causes 1) systemic blood vessel vasodilation, which decreases peripheral resistance 2) increased GFR, which increases urine output, and 3) increased loss of sodium and water in the kidneys, which increases urine output. Both the decrease in peripheral resistance and increased urine output (which decreases blood volume) result in a decrease in blood pressure. These processes are facilitated by ANP also inhibiting the release of renin, aldosterone, and ADH, as well as it interfering with the action of angiotensin II. 16. Sodium is the principal cation in extracellular fluid and thus an important factor in establishing the osmolarity of blood. It has neuromuscular functions and is the most important electrolyte in determining both blood plasma osmolarity and regulating fluid balance. Aldosterone induces the reabsorption of Na+ in the kidneys. ADH causes the reabsorption of water in the kidneys which decreases the overall concentration of Na+ in the blood.

ANP decreases Na+ retention in the kidneys.

17. In response to an increase in blood plasma H+ concentrations, type A intercalated cells in the kidneys secrete H+ into tubular fluid and reabsorb HCO3- to raise blood pH. 18. During hyperventilation, the increase in respiratory rate causes elevated levels of CO2 to be expired, thus blood CO2 levels decrease. This causes the H+ concentration in the blood to decrease resulting in an increase in blood pH. 19. Proteins (which are polymers composed of amino acids) serve as a chemical buffering system—both within cells and in blood plasma. Proteins account for approximately three-quarters of the body’s chemical buffering.

The amine groups of amino acids act as weak bases (and bind hydrogen ions) and the carboxylic acid of amino acids act as weak acids (and releases hydrogen ions).

The phosphate buffering system buffers intracellular fluid. Phosphates are abundant intracellular ions that can form both HPO42- (a weak base that binds hydrogen ions) and H2PO4− (a weak acid that releases hydrogen ions) in an aqueous environment.

The bicarbonate buffer system buffers blood and extracellular fluid (it is the most important buffering system in the ECF). In an aqueous environment, bicarbonate HCO3-, a weak base, binds hydrogen ions, and H2CO3, a weak acid, releases hydrogen ions.

20. In respiratory acidosis, the respiratory rate decreases and blood CO2 increases, producing increased carbonic acid. The kidneys compensate with increased secretion of H+ and increased reabsorption of HCO3-. The increase in blood HCO3- from renal compensation, if sufficient, reestablishes acid-base balance.

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: Vomiting, diarrhea, and decreased water intake all cause dehydration.

2. B Feedback: Extracellular K+ levels are usually very low. Upon damage to cells, K+ was released from ICF, raising levels in the ECF.

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3. D Feedback: Water is a hypotonic to blood plasma. Drinking water without supplementing electrolytes will cause hypotonic hydration.

4. B Feedback: Ketoacidosis is a metabolic disorder associated with elevated fatty acid metabolism with an increase in production of ketoacids. The elevated ketoacids can result in metabolic acidosis.

5. A Feedback: Harold’s blood lab results would most likely show decreased HCO3−; caused by the primary disturbance and decreased PCO2 caused by compensation.

Answers to “Can You Synthesize What You’ve Learned?”

1. Aldosterone causes the retention of Na+ and water, as well as the secretion of K+ in the kidneys. Thus, blood concentration for Na+ would be elevated, blood concentration for K+ would be low, and blood pressure would be increased (due to the retention of higher than normal levels of Na+ and water).

2. The primary disturbance is metabolic alkalosis (due to vomiting and loss of H+). High level of CO2 in the blood would indicate respiratory compensation. The pH of her blood is within the normal range; hence, compensation is adequate.

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Chapter 26 Answers to “What Did You Learn?”

1. The primary difference between mechanical digestion and chemical digestions is that mechanical digestion occurs when ingested material is physically broken down into smaller units by chewing and mixing without changing its chemical structure, whereas chemical digestion breaks down large molecules into smaller molecules by breaking chemical bonds.

2. The gastrointestinal tract (also called the digestive tract) forms a continuous tube that includes the oral cavity (mouth), pharynx (throat), esophagus, stomach, small intestine, and large intestine, and ends at the anus.

Accessory digestive organs assist in the digestion of food and include: salivary glands, liver, pancreas, teeth, tongue and gallbladder.

3. Substances must cross the epithelium of the mucosa before being absorbed into either the blood or lymphatic capillaries.

4. A muscular sphincter closes off the lumen at some point along the GI tract, and in so doing it can control the movement of materials into the next section of the GI tract.

5. Peristalsis is an alternating contraction sequence of muscle layers for the purpose of propelling ingested materials through the GI tract. Mixing is a back-and-forth motion that occurs at any point in time within different regions of the GI tract but lacks directional movement. It is for blending ingested materials with secretions.

6. Intraperitoneal organs are within the abdomen and completely surrounded by visceral peritoneum. They include the stomach, most of the small intestine (jejunum and ileum), and parts of the large intestine (transverse colon, sigmoid colon). Retroperitoneal organs lie outside of the parietal peritoneum directly against the posterior abdominal wall, so only their anterolateral portions are covered with the parietal peritoneum.

7. The greater omentum extends inferiorly from the inferolateral surface (greater curvature) of the stomach and covers most of the abdominal organs.

8. Yes. Autonomic interactions of the CNS that help regulate digestive system processes are described as long reflexes.

9. Gastrin (released from the stomach), and both secretin and cholecystokinin (released from the small intestine) are the three primary hormones that participate in the regulation of the digestive processes.

10. The upper gastrointestinal tract structures include the oral cavity and salivary glands, pharynx, esophagus, and stomach (as well as the duodenum).

11. A bolus is a wet mass formed when ingested materials mix with saliva in the oral cavity. The tongue manipulates and mixes ingested materials during chewing and helps compress the partially digested materials against the palate to assist in mechanical digestion. Teeth are responsible for mastication which is the chewing, tearing and grinding of food as it gets mixed with saliva. Salivary glands produce saliva, which is composed of water and a mixture of solutes. Saliva moistens ingested food, initiates the chemical breakdown of starch, acts as a watery medium into which food molecules are dissolved so taste receptors may be stimulated, cleanses oral cavity structures, and helps inhibit bacterial growth.

12. The mucosa of the esophagus is lined by a nonkeratinized, stratified squamous epithelium rather than a simple columnar epithelium. This epithelium serves to protect the gastrointestinal wall from abrasion as the bolus is swallowed. The muscularis layer is unique in that it contains a blend of both skeletal and smooth muscle. The superior one-third of the esophageal muscularis consists of skeletal muscle to ensure that the swallowed material moves rapidly out of the pharynx and into the esophagus before the next respiratory cycle begins. The middle one-third of the esophageal muscularis has an intermingling of both skeletal and smooth muscle cells, and the distal one-third contains only smooth muscle.

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13. The three phases of swallowing are the (1) voluntary phase, (2) pharyngeal phase, and (3) esophageal phase. In the voluntary phase of swallowing, the bolus of food is pushed by tongue against hard palate and then moves toward the oropharynx. In the pharyngeal phase, as the bolus moves into the oropharynx, the soft palate and uvula close off nasopharynx, and the larynx elevates so the epiglottis closes over the laryngeal opening. In the esophageal phase, peristaltic contractions of esophageal muscle push the bolus toward the stomach.

14. There are five secretory cell types in the stomach: surface mucous cells, mucous neck cells, parietal cells, chief cells, and G-cells. 1) Surface mucous cells continuously produce an alkaline mucin that helps prevent ulceration of the stomach lining upon exposure to both the high acidity of the gastric fluid and gastric enzymes. 2) Mucous neck cells produce an acidic mucin that helps maintain the acidic conditions in the stomach resulting from the secretion of hydrochloric acid by parietal cells. Both types of mucous cells have lubricating properties to protect the stomach lining from abrasion or mechanical injury. 3) Parietal cells produce both intrinsic factor which is involved in absorption of vitamin B12 in the small intestine and hydrochloric acid which activates pepsinogen into pepsin, kills microorganisms that enter the stomach, denatures proteins, and helps breakdown plant cell walls and animal connective tissue. 4) Chief cells produce and secrete pepsinogen, an inactive precursor of the protease pepsin. Chief cells also produce gastric lipase which assists in fat digestion. 5) G-cells secrete gastrin, a hormone that regulates gastric secretions and motility.

15. The gastric reflex is initiated as food enters the stomach. Baroreceptors in the wall of the stomach detect increased distension in the stomach wall, and chemoreceptors detect both protein and an increase in pH of gastric contents. Proteins buffer H+ and increase pH. Increased nerve signals are relayed along sensory neurons to the medulla oblongata, which results in increased nerve signals relayed to the stomach. An increase in stomach motility and an increase in secretory activity of gastric cells results.

16. The small intestine (except the duodenum), the large intestine, and accessory organs (liver, gall bladder and pancreas) comprise the organs of the lower gastrointestinal tract.

17. Increased surface area in the small intestine results from: 1) circular folds (plicae circulares), which are inward folds of the mucosa and submucosa that line the lumen of the small intestines; (2) villi, which are small, fingerlike projections of the mucosa; and (3) microvilli, which are extensions of the plasma membrane of the simple columnar epithelial cells lining the small intestine.

18. Segmentation mixes chyme with secretions in the small intestines through a ‘back-and-forward’ motion.

19. Blood that is deoxygenated and nutrient rich enters the liver in the hepatic portal vein while blood that is oxygenated enters the liver in the hepatic artery. They merge within the hepatic sinusoids of the liver lobules.

20. The liver does not produce digestive enzymes. It secretes bile, an alkaline fluid that assists with the mechanical digestion of lipids.

21. Pancreatic juice contains water, bicarbonate ions, and a mix of digestive enzymes. The bicarbonate neutralizes acid from the stomach. The digestive enzymes break down nutrients into smaller chemical structures. The enzymes include: amylase to digest carbohydrates, lipase to digest lipids, several inactive proteases that when activated digest proteins, and nucleases to digest nucleic acids.

22. Chyme will pass through the ileocecal valve to enter the cecum. From there it will be moved through the ascending colon, right colic flexure, transverse colon, left colic flexure, descending colon, sigmoid colon, rectum, and then through the anal canal before being eliminated from the body.

23. The bacterial flora (termed the indigenous microbiota) of the large intestines are responsible for the chemical breakdown of complex carbohydrates, proteins, and lipids that remain in the chyme after it has passed through the small intestine. Bacteria also produce B vitamins and vitamin K, which are then absorbed from the large intestine into the blood.

24. The large intestine absorbs water and electrolytes (primarily Na+ and Cl-) and vitamins B and K that are produced by bacterial flora.

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25. Starch breakdown begins in the oral cavity. It is catalyzed by salivary amylase synthesized and released from the salivary glands. Salivary amylase breaks the chemical bonds between glucose molecules within the starch molecule to partially digest the starch molecule. The longer the salivary amylase acts the greater the digestion of the starch molecule. When the bolus is swallowed, the low pH in the stomach inactivates the salivary amylase. Pancreatic amylase is synthesized and released by the pancreas into the small intestine. It further digests starch into shorter strands of glucose molecules (oligosaccharides), maltose (disaccharide of glucose), and glucose. Brush border enzymes in the small intestine then complete the breakdown process; the enzymes dextrinase and glucoamylase digest oligosaccharides into maltose, while maltase digests the disaccharide maltose into glucose monomers.

26. Pepsinogen is released from chief cells of the gastric mucosa, and is then activated by the low pH in the stomach into pepsin. Trypsinogen, released from the pancreas, is converted to trypsin, its active form, by the enzyme enteropeptidase. Trypsin then activates additional molecules of trypsinogen to trypsin, as well as chymotrypsinogen into chymotrypsin, and procarboxypeptidase into carboxypeptidase. This mechanism of storing proteases in an inactive form until they are needed is to protect cells (and the pancreatic ducts) from digestion by these enzymes.

27. Bile salts act to emulsify lipids. This is a form of mechanical, not chemical, digestion because the lipid droplets are separated into smaller droplets called micelles by the action of the bile but chemical bonds are not broken.

28. Nucleic acid digestion occurs in the small intestines.

Answers to “Do You Know the Basics?”

1. A Feedback: The liver occupies most of the upper right quadrant of the abdomen.

2. B Feedback: Parietal cells are responsible for the formation of HCl (and intrinsic factor).

3. B Feedback: Absorption of digested product(s) is not a regulated process.

4. C Feedback: Retroperitoneal digestive organs include most of the duodenum, the pancreas, ascending and descending colon, and the rectum.

5. A Feedback: Pancreatic juice contains bicarbonate ion from the pancreatic ducts and digestive enzymes from pancreatic acini.

6. C Feedback: The cystic duct is part of the biliary apparatus and it transports bile from the gallbladder to the common bile duct.

7. B Feedback: Protein digestion begins with pepsin in the stomach.

8. B Feedback: Micelles facilitate the digestion and absorption of lipids (including triglycerides) in an aqueous environment.

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9. C Feedback: Most digestive enzymes, with the exception of salivary amylase, lingual and gastric lipase, pepsin, and brush border enzymes, are produced in the pancreas and released as part of the pancreatic juice.

10. C Feedback: With the exception of some complex carbohydrate digestion in the mouth, and some protein digestion in the stomach, most digestion occurs in the small intestines.

11. The GI tract consists of four layers (from innermost to outermost): a mucosa lining the lumen, a submucosa, a muscularis layer, and an outer covering of either serosa or adventitia. The esophagus has the following features in its tunics: 1) A mucosa that is composed of a nonkeratinized stratified squamous epithelium. 2) A submucosa that is thick and composed of abundant elastic fibers that permit distension during swallowing, and houses numerous mucous glands that provide thick, lubricating mucus for the epithelium. 3) A unique muscularis that contains a blend of both skeletal and smooth muscle and is divided into three parts, including a) a superior one-third that is all skeletal muscle in order to rapidly move material out of the pharynx into the esophagus, b) a middle one-third that has intermingling skeletal and smooth muscle fibers, and c) an inferior one-third that has only smooth muscle fibers. (4) An outermost layer that is an adventitia.

12. The two layers of skeletal muscle in the superior one-third of the esophageal muscularis ensure that the swallowed material moves rapidly out of the pharynx and into the esophagus before the next respiratory cycle begins. This is because skeletal muscle contractions occur more rapidly than does smooth muscle contraction.

13. Intrinsic factor is released only by parietal cells. It is required for the absorption of vitamin B12 in the small intestine. All other functions of the stomach (storage, mixing, secretion) may be taken over by the small intestine as shown by the results of gastric bypass surgery.

14. Circular folds of the mucosa and submucosa are inward folds of the mucosal and submucosal tunics that extend toward the lumen of the small intestine. They increase the surface area for absorption and act as ‘speed bumps’ to slow the movement of chyme through the lumen of the small intestine. Villi are small fingerlike projections of the mucosa extending into the lumen of the small intestine. Microvilli are extensions of the plasma membrane of the simple columnar epithelial cells lining the small intestine.

15. Abundant mucus secretion is required to lubricate the undigested material and facilitate its passage through the large intestine.

16. Proteases are produced and stored in an inactive form to prevent the destruction of the proteins in the cells that form these enzymes (and pancreatic ducts for those synthesized by the pancreas).

17. The gallbladder stores, concentrates, and releases bile that is produced by the liver.

18. (1) Mastication is the mechanical digestion in the oral cavity (also called chewing). It requires the coordinated activities of teeth, skeletal muscles in lips, tongue, cheeks, and jaws that are coordinated by the mastication center. (2) Gastric mixing is a form of mechanical digestion in the stomach that changes the semidigested bolus into chyme. Contractions of the stomach’s thick muscularis layer churn and mix the bolus with the gastric secretions, leading to a reduction in the size of swallowed particles. (3) Segmentation is the primary form of mechanical digestion in the small intestine. Muscle contractions cause a “backward-andforward” motion that facilitates the mixing of chyme (that was received from the stomach) with accessory gland secretions (from the liver, gallbladder, and pancreas.

19. Pepsin breaks peptide bonds between amino acid composing proteins. In addition, lingual lipase (produced by intrinsic salivary glands in the mouth) is activated in the low pH of the stomach, and along with gastric lipase (an enzyme produced by chief cells of the stomach) digests approximately 30% of the triglycerides to diglyceride and a fatty acid. Neither of these lipase enzymes requires the participation of bile salts (see next section).

20. Digested fats and lipids are transported by micelles to the epithelial cells that line the small intestine and absorbed across the apical surface of these cells. In the epithelial cells, the lipids are wrapped in proteins to form

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chylomicrons. The Golgi apparatus packages chylomicrons into secretory vesicles, and released basolaterally from the cells by exocytosis. Once in the interstitial fluid, they enter lacteals and are delivered by the lymphatic system to the vena cava.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: The one critical function of the stomach is the production of intrinsic factor. Intrinsic factor is critical for the absorption of vitamin B12 in the small intestines.

2. B Feedback: The gallbladder stores and concentrates bile, which is critical for mechanical digestion of lipid (through formation of micelles).

3. A Feedback: The small intestine is responsible for the digestion and absorption of nearly all nutrients.

4. C Feedback: Insufficient digestive enzymes (which are produced in the pancreas) reach the small intestine if the pancreatic ducts are blocked.

5. A Feedback: Appendicitis results from a bacterial infection in the vermiform appendix. Rupture of the appendix releases these pathogens in the abdominal cavity.

Answers to “Can You Synthesize What You’ve Learned?”

1. In response to an infection the gastrointestinal tract may attempt to expel pathogens by (1) vomiting, which expels stomach contents through the oral cavity and (2) diarrhea, which expels the contents of the large intestine through the anal canal.

2. HCl is not produced in parietal cells; rather it is produced as a result of processes that occur in parietal cells.

Water is split within the parietal cells into a hydrogen ion and a hydroxide ion. The hydrogen ion is pumped into the lumen of the gastric pit by an H+/K+ pump. Hydroxyl ions combine with carbon dioxide to form bicarbonate ions. An exchange occurs as bicarbonate is transported out of the parietal cell (bicarbonate enters the blood), while chloride ion (Cl-) is transported into the parietal cell; Cl- then enters the lumen of the gastric gland. Within the lumen of the gastric gland, Cl- combines with H+ to form hydrochloric acid (HCl).

3. Absorption of fluids, and the subsequent compaction of feces, occurs along the length of the large intestines.

The distal portion of the colon is thought to be exposed to toxins in the fecal matter for longer periods of time, increasing the probability of causing polyps or colorectal cancer.

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Chapter 27 Answers to “What Did You Learn?”

1. Nutrients required by the body include: carbohydrates, lipids, proteins, vitamins, minerals, and water.

2. Macronutrients must be consumed in relatively large quantities. All macronutrients are organic biomolecules.

They include carbohydrates, lipids, and proteins. Micronutrients must be consumed in relatively small quantities and include both vitamins and minerals.

3. RDA is the recommended daily allowance established by the Food and Nutrition Board of the National Academy of Sciences.

4. Sugars include both monosaccharides (glucose, fructose, and galactose) and disaccharides (sucrose, lactose, and maltose). Starch is a polysaccharide polymer of glucose molecules. Both sugars and starch are usually converted to glucose, which is one of the primary nutrients supplying energy to cells.

5. Dietary fiber includes the fibrous molecules (e.g., cellulose) of both plants and animals that cannot be chemically digested and absorbed. Rather it remains within the lumen of the gastrointestinal tract and adds bulk.

This bulk stimulates peristalsis of the large intestine, which facilitates the movement of the GI tract contents and their ultimate elimination as a component of feces.

6. Fat in the diet has two major functions. (1) Triglycerides are a primary nutrient supplying energy to cells.

(2) Fat is necessary for the absorption of fat-soluble vitamins (vitamins A, D, E, and K).

7. Animal proteins (meats, poultry, fish, eggs, milk, cheese, and yogurt) are complete proteins which contain all of the essential amino acids. Plant proteins (legumes, vegetables, and grains) tend to be lacking in one or more of the essential amino acids and thus they are incomplete proteins.

8. A vegetarian is an individual who does not eat meat, fish, or poultry. They must be aware that plant-based protein sources are often individually incomplete. Thus, vegetarians must be sure to obtain the essential amino acids from a variety of complementary protein sources. The balanced food combinations do not need to be eaten in the same meal, but when eaten regularly they may supply the necessary essential amino acids.

9. Water-soluble vitamins dissolve in water: they include both B-complex vitamins and vitamin C. Vitamins A, D, E, and K are fat-soluble. If dietary intake of fat-soluble vitamins exceeds body requirements, the excess is stored within the body fat and may reach toxic levels.

10.Major minerals are needed at levels greater than 100 milligrams per day, and trace minerals are required at less than 100 milligrams per day. Major minerals include calcium, chloride, magnesium, phosphorus, potassium, sodium, and sulfur; trace minerals include chromium, cobalt, copper, fluoride, iodine, iron, manganese, molybdenum, selenium, and zinc.

11.The USDA MyPlate schematic has five food categories: fruits, grains, vegetables, proteins, and dairy.

The largest portion is vegetables.

12.Nutritional labeling may be helpful for those who are interested in eating a healthy diet, those who are meal planning for weight-loss programs, and individuals who are restricting intake of nutrients such as sugar or sodium.

13.During the absorptive state, the concentration of glucose, triglycerides, and amino acids are increasing within the blood as they are absorbed from the GI tract. Insulin is the major regulatory hormone released during the absorptive state, and it results in a decrease in all energy-releasing (glucose, triglycerides, and amino acids) molecules in the blood, an increase in the storage of glycogen and triglycerides, and the formation of protein with body tissues.

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14. During the postabsorptive state, glucagon is the major regulatory hormone that is released. It stimulates (1) glycogenolysis, which increases blood glucose levels and (2) lipolysis, which increases blood glycerol and fatty acid levels.

15. Blood enters the liver lobule through either a branch of the hepatic portal vein or a branch of the hepatic artery.

Blood from both vessels merges within sinusoids of the lobule, as it percolates through hepatocytes, on its way to the central vein at the center of the lobule. (Blood is transported out of the liver by the hepatic veins into the inferior vena cava.)

16. Cholesterol synthesis decreases with a high dietary intake of cholesterol. Newly synthesized cholesterol is either (1) released into the blood as a component of VLDLs or (2) synthesized into bile salts and released as a component of bile into the small intestine.

17. HDLs transport cholesterol from peripheral tissues to the liver.

18. All of the following are specific examples of each of the five major functions of the liver that are presented visually in the figure in the text.

Carbohydrate metabolism: The liver is able to convert other monosaccharides (e.g., fructose and galactose) to glucose, convert noncarbohydrate molecules into glucose by gluconeogenesis, produce glycogen from glucose by glycogenesis, synthesize (and store) glycogen by glycogenesis, and digest glycogen into glucose by glycogenolysis.

Protein metabolism: The liver is responsible for the deamination of amino acids (and formation of urea), transamination of one amino acid for another, and the synthesis of plasma proteins.

Lipid metabolism: Lipid metabolism in the liver includes triglyceride synthesis by lipogenesis, release of fatty acids by digesting triglycerides into glycerol and fatty acids through lipolysis, conversion of acetyl CoA into ketone bodies, as well as cholesterol and bile salt synthesis.

Transport of lipids: The liver produces lipoproteins which transport lipids through the blood. Very low-density lipoproteins (VLDLs) and low-density lipoproteins (LDLs) transport lipids for storage within tissue. High-density lipoproteins (HDLs) transport lipids from tissues to the liver.

Other functions: The liver is also responsible for elimination of bilirubin from blood, detoxification of drugs, hormone catabolism, and storage of vitamins A, D, and B12, as well as storage of numerous minerals such as Fe, Zn, Cu, Mg, and Mn. 19. Glycerol enters the cellular respiration pathway of glycolysis. Beta-oxidation of fatty acids produces acetyl CoA which enters the citric acid cycle. Deaminated amino acids may enter cellular respiration during glycolysis, the intermediate stage, or at specific points in the citric acid cycle (depending upon the specific amino acid).

20. Excess glucose is broken down into acetyl CoA that is synthesized into fatty acids and then combined with glycerol to form triglycerides.

21. Metabolic rate increases with exposure to cold temperatures. The increase in BMR helps increase body temperature.

22. The core body temperature is the temperature of the vital portions of the body, which consists of the head and torso. The temperature of these regions must be kept relatively constant or stable to assure that life is maintained.

23. In response to an increase in body temperature the hypothalamus stimulates sweat glands and causes vasodilation of blood vessels in the skin. Both facilitate the release of heat from the body’s surface.

Answers to “Do You Know the Basics?”

1. D Feedback: Proteins, minerals, and vitamins are all nutrients.

2. C Feedback: B-complex vitamins serve as coenzymes in various enzymatic chemical reactions.

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3. A Feedback: Potatoes contain large amounts of the macronutrient starch, a carbohydrate.

4. C Feedback: Insulin is released during the absorptive state associated with a meal, which facilitates the storage of nutrients.

5. D Feedback: Insulin induces the uptake of amino acids into muscle cells, hepatocytes to form glycogen from glucose (glycogenesis), and the formation of triglycerides from glycerol and fatty acids (lipogenesis).

6. D Feedback: Numerous molecules can be catabolized in cellular respiration, including glucose, deaminated amino acids, and fatty acids.

7. B Feedback: Metabolism increases from the resting to the absorptive state after a meal, interfering with basal metabolic function.

8. D Feedback: The total metabolic rate increases to accommodate the digestion and absorption of nutrients following a meal.

9. A Feedback: Insulin is not released by the liver; insulin is released from the pancreas.

10. B Feedback: Thyroid hormone stimulates the activity of Na+/K+ pumps in neurons. This requires energy from ATP, and increases body temperature.

11. Nutrition is the study of the means by which living organisms acquire the nutrients they need to grow and sustain life.

12. Vitamin C (or ascorbic acid) is required for the synthesis of collagen (an important protein in connective tissue) and (along with vitamins A and K) functions as an antioxidant by removing free radicals (damaging chemical structures that contain unpaired electrons).

13. Nonessential amino acids can be made in the body. Essential amino acids must come from the diet.

14. If dietary intake of fat-soluble vitamins exceeds body requirements (generally caused by excessive intake through supplements), the surplus is stored within the body fat and may reach toxic levels (hypervitaminosis).

15. Minerals are inorganic ions such as iron, calcium, sodium, potassium, iodine, zinc, magnesium, and phosphorous. Examples of their function in the body include: 1) iron binding oxygen to hemoglobin within erythrocytes, 2) calcium required for formation and maintenance of the skeleton, muscle contraction, and blood clotting, 3) sodium and potassium establishing resting membrane potentials within excitable cells and required in the generation of action potentials, 4) iodine needed to produce thyroid hormone; and (5) zinc which has roles in both protein synthesis and wound healing.

16. Nitrogen balance occurs when equilibrium exists between its dietary intake and its loss in urine and feces.

Input of nitrogen must equal output of nitrogen to maintain a nitrogen balance. A positive nitrogen balance occurs when an individual absorbs more nitrogen than is excreted, such as occurs in individuals who are growing, pregnant, or recovering from injury. A negative nitrogen balance occurs when more nitrogen is excreted than is absorbed; this condition might result from malnutrition or blood loss.

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17. The postabsorptive state is the time between meals when the body relies on its stores of nutrients because no further absorption of nutrients is occurring. The major regulatory hormone that is released during this time is glucagon. Glucagon stimulates liver cells to engage in catabolism of glycogen to glucose by increasing glycogenolysis. Glucagon may also increase the formation of glucose from noncarbohydrate sources by stimulating gluconeogenesis. Glucagon also causes adipose connective tissue to break down triglycerides to glycerol and fatty acids by stimulating lipolysis.

18. Lipid is transported by a lipid and protein wrap called a lipoprotein. The liver functions in synthesizing both very-low density lipoproteins (VLDLs) and low-density lipoproteins (LDLs), which transport triglycerides and cholesterol from the liver to peripheral tissues, primarily adipose connective tissue. It also synthesizes the proteins for high-density lipoproteins, which transport lipid from peripheral tissue to the liver.

19. The liver is able to convert monosaccharides (fructose and galactose) into glucose. It can convert noncarbohydrates absorbed from the blood into glucose by gluconeogenesis. Glycogen molecules are formed from glucose by glycogenesis, and then glucose will be released as needed by glycogenolysis. The liver is also responsible for the deamination of amino acids and then the conversion of NH2 to urea which is eliminated by the kidney while the remaining components are oxidized to generate ATP. Amino acids are used to form new proteins, and transamination of one amino acid for another occurs in the liver. Lipid metabolism in the liver includes triglyceride synthesis by lipogenesis, release of fatty acids by lipolysis, breakdown of fatty acids into acetyl CoA (beta oxidation), and conversion of acetyl CoA into ketone bodies, as well as cholesterol and bile salt synthesis.

20. The hypothalamus detects body temperature changes as blood passes through it. In order to retain heat, the hypothalamus will prevent sweating by cessation of stimulation of sweat glands. It will stimulate muscle contraction, causing the body to shiver, and it will constrict peripheral blood vessels, thereby preventing the loss of heat to the external environment. At the same time, the most significant hormonal effect is the release of thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary gland to release thyroid-stimulating hormone (TSH). TSH stimulates the thyroid gland to release thyroid hormone, which will stimulate an increase in metabolic rate of almost all cells, especially neurons. Na+/K+ pump activity in neurons generates heat as a byproduct.

Answers to “Can You Apply What You’ve Learned?”

1. B Feedback: Meat, fish, and poultry contain plentiful essential amino acids. Substitutes such as beans or nuts rarely possess all of the essential amino acids, and must therefore be taken in correct combinations to ensure that all of the essential amino acids are acquired.

2. A Feedback: The hypothalamus is responsible for thermoregulation, which includes initiating sweating and shivering.

3. D Feedback: If dietary intake of fat-soluble vitamins exceeds body requirements, the excess is stored within the body fat and may reach toxic levels.

4. A Feedback: Thyroid hormone is produced by the thyroid gland. It is heavily dependent upon the availability of iodine, and stimulation from the pituitary gland, but it is not associated with liver function.

5. C Feedback: Gluconeogenesis in the liver converts stored molecules, such as fatty acids, into glucose.

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Answers to “Can You Synthesize What You’ve Learned?”

1. The MyPlate schematic presents a visual representation of the proportion of food that must come from a particular food category in order to maintain an appropriate, healthy diet.

2. Meat, fish, and poultry contain plentiful essential amino acids. In a vegetarian diet, these are not available.

Plant substitutes such as beans or nuts rarely possess all of the essential amino acids, and must therefore be taken in correct combinations to ensure that all of the essential amino acids are acquired.

3. Frostbite is damage to superficial cells due to exposure to extreme cold. Damage occurs due to extensive and prolonged vasoconstriction of blood vessels as a result of exposure to extreme cold. This results in oxygen deprivation and tissue death.

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Chapter 28 Answers to “What Did You Learn?”

1. Both the male and female reproductive systems consist of gonads (ovaries in females and testes in males) which produce sex cells called gametes. Gonads also produce sex hormones. Both sexes also have accessory reproductive organs.

2. Gonadotropin-releasing hormone (GnRH) is released from the hypothalamus at puberty. This hormone acts on specific endocrine cells in the anterior pituitary and stimulates them to release the gonadotropins follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

3. The urogenital triangle contains the urethral and vaginal orifices in females and the base of the penis and the scrotum in males.

4. Sex hormones primarily determine whether an individual is female (two X chromosomes) or male (and X and a Y chromosome) although they also contain genes that code for cellular functions. Autosomes contain genes that code for cellular functions and help determine most human characteristics.

5. Gametes must be haploid, so that when they combine during fertilization, one member of each pair of chromosomes that form the diploid embryo is inherited from each parent.

6. 1) Mitosis produces two daughter cells that are genetically identical to the parent cell. In contrast, meiosis produces four daughter cells that are genetically different from the parent cell. 2) Mitosis produces daughter cells that are diploid, whereas meiosis produces daughter cells that are haploid. 3) Meiosis includes a process called crossing over, whereby genetic material is exchanged between homologous chromosomes.

7. Prior to meiosis, the DNA in each chromosome is replicated (duplicated exactly) in the parent cell during interphase. These replicated chromosomes (also known as double-stranded chromosomes) are composed of two identical structures called sister chromatids. Each sister chromatid contains an identical copy of DNA at this point. The sister chromatids are attached at a specialized region termed the centromere.

The term homologous chromosome refers to each matching chromosome (called an autosome) that contains genes which code for cellular functions. The pair is called homologous chromosomes—one is a maternal copy, the other is a paternal copy.

8. Independent assortment occurs during Metaphase I, and it is the random alignment of homologous chromosomes along the center of the cell. Both crossing over and independent assortment ensure genetic diversity in the production of gametes.

9. The process by which maternal and paternal chromosome pairs are separated and move to opposite ends of the cell in Anaphase I is referred to as reduction division. It is necessary to assure that each daughter cell receives only one-half the starting number of chromosomes [only 23 chromosomes of the original 23 pairs].

10. Daughter cells become haploid during Telophase II of meiosis.

11. Collectively, the broad ligament, ovarian ligament, and suspensory ligament are connective tissue cords and sheets that support the uterus and ovary. The broad ligament is an extension of the peritoneum that drapes over the uterus. Each ovary is attached to the posterior aspect of the broad ligament by the ovarian ligament, which is the superior portion of the round ligament of the uterus. The suspensory ligament attaches to the lateral edge of each ovary and projects superolaterally to the pelvic wall.

12. Primordial, primary, secondary and mature follicles are all similar in that they each contain an oocyte that is surrounded by follicle cells. The primordial, primary and secondary follicles each contain a primary oocyte,

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while the mature follicle contains a secondary oocyte. Further, the shape and number of follicle cells differ among the different types of follicles.

13. At birth, all follicles are primordial follicles. After puberty, under the control of follicle-stimulating hormone, a few of the follicles will start to develop into primary, secondary, and eventually vesicular follicles.

14. FSH triggers the development of primordial follicles. LH causes an increase in fluid volume within the antrum near the midpoint of the cycle (and the oocyte is forced toward the side of the follicle), ultimately leading to ovulation which is the release of the secondary oocyte.

15. The follicular phase of the ovarian cycle is typically the first half of the cycle and it involves the growth and maturation of follicles (about 20) from the primordial to the mature stage (usually only one). This is associated with increasing levels of estrogen. Ovulation is the release of a secondary oocyte from the mature follicle. It is induced by a peak in LH secretion and typically it occurs midway through the ovarian cycle. The luteal phase is typically the last half of the cycle. The remaining granulosa cells in the mature follicle become the corpus luteum.

It secretes progesterone and estrogen to stabilize and build the uterine lining for possible implantation of a fertilized oocyte.

16. The infundibulum is the free, funnel-shaped lateral margin of the uterine tube and it possesses fimbriae that surround the ovary and bring the ovulated oocyte into the uterine tube. The ampulla is an expanded region that is typically the site of fertilization. The isthmus conducts the fertilized oocyte from the ampulla to the uterine wall.

The uterine part of the uterine tube extends medially, through the uterine wall and transports the fertilized oocyte into the lumen of the uterus.

17. The perimetrium is a serosa and the outermost tunic. The myometrium consists of three intertwining layers of smooth muscle, which produce the strong muscular contractions associated with childbirth. The endometrium is an intricate mucosa composed of a simple columnar epithelium and an underlying lamina propria filled with compound tubular glands (called uterine glands) that enlarge during the uterine cycle. Two distinct layers form the endometrium: a deeper basal layer adjacent to the myometrium (a permanent layer that undergoes few changes during the uterine cycle) and a superficial functional layer that grows during each uterine cycle and is shed at menses. It is the site of implantation.

18. The vagina is a thick, elongated fibromuscular tube that 1) connects the uterus with the outside of the body and functions as the birth canal, 2) receives the penis during intercourse, and 3) it serves as the passageway for menstruation.

19. The three phases of the uterine cycle are the menstrual phase, proliferative phase, and the secretory phase.

1) The menstrual phase of the uterine cycle (between approximately days 1–5) is characterized by loss of the stratum functionalis (functional layer) of the endometrium. 2) The proliferative phase (between approximately days 6–14) is the time of initial development of the new functional layer of the endometrium. It overlaps the time of follicle growth and estrogen secretion by the ovary. 3) The secretory phase (between days 15–28) is marked by increased vascularization and development of uterine glands in response to progesterone secretion from the corpus luteum.

20. 1) The beginning of the ovarian cycle (the start of the follicular phase with stimulation of follicle development in the ovary) overlaps with the end of the previous uterine cycle (menstrual phase and sloughing of its functional layer). 2) The ovarian cycle continues with the follicular phase up to its mid-point (and then ovulation occurs). This continuation of the follicular phase overlaps with the beginning of the proliferative phase in the uterus and the initial development of its new functional layer. 3) After ovulation: a) the ovary enters the luteal phase in which the remaining follicular cells in the ovary develop into the corpus luteum, and this structure secretes large amounts of estrogen, progesterone and inhibin in order to continue building the uterine lining while inhibiting the hypothalamus and anterior pituitary from further oocyte development, and b) the uterus enters the secretory phase where its vascularization is increased and uterine glands develop.

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21. The external reproductive organs of the female are termed the external genitalia, or vulva. The mons pubis is an expanse of skin and subcutaneous connective tissue immediately anterior to the pubic symphysis. The labia majora are paired, thickened folds of skin and connective tissue that contain numerous sweat and sebaceous glands. The labia minora are paired folds immediately internal to the labia majora. The space between the labia minora is the vestibule: both the urethral opening and vaginal orifice are here. Erectile bodies (bulbs of the vestibule) and paired greater vestibular glands are housed within the vestibule walls; they secrete mucin that acts as a lubricant for the vagina. The clitoris is an erectile body that contains numerous sensory nerve receptors which provide pleasure to the female during sexual intercourse.

22. The suspensory ligaments are fibrous connective tissue bands that suspend the lobes of the mammary glands.

Individual lobes contain smaller compartments called lobules; the secretory units of the lobules, called alveoli, produce milk. The milk drains into tiny ducts, which merge to form large lactiferous ducts that drain milk from a single lobe of the breast.

23. Prolactin is a hormone produced in the anterior pituitary that causes the mammary gland to grow and form more alveoli. It is responsible for milk production. Oxytocin is a hormone released from the posterior pituitary and is responsible for milk ejection.

24. 1) The excitement phase stimulates female reproductive structures including the mammary glands, clitoris, vaginal wall, bulbs of the vestibule, and labia, which all become engorged with blood. 2) During orgasm the woman may experience intense feelings of pleasure, release of tension, and some pelvic throbbing. The vagina and uterus contract rhythmically for many seconds. 3) The resolution phase includes the return of the uterus to its original position and relaxation of the vaginal wall. Excess blood leaves the other reproductive organs.

25. When the testes are exposed to elevated temperatures, the dartos muscle in the scrotum wall relaxes, allowing the testes to move inferiorly away from the body. This movement cools the testes.

26. Seminiferous tubules contain 1) sustentacular cells, which are nondividing support cells, and 2) a population of dividing germ cells that continuously produce sperm beginning at puberty. These germ cells include spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids, and sperm.

27. Interstitial cells produce androgens; the most common one is testosterone. Testosterone inhibits GnRH secretion from the hypothalamus and reduces the sensitivity of the anterior pituitary to GnRH. Sustentacular cells produce inhibin, which inhibits FSH secretion from the anterior pituitary gland.

28. A spermatogonium is a diploid cell that is called a germ cell. It has 46 chromosomes. Mitotic division of a spermatogonium produces a new germ cell and a committed cell called a primary spermatocyte. Meiosis I begins in the diploid primary spermatocyte. Cells called secondary spermatocytes are haploid cells with 23 chromosomes that are produced during meiosis I. Meiosis II originates with the secondary spermatocytes and produces spermatids. The process of spermiogenesis begins with spermatids and results in morphologic changes to produce spermatozoa.

29. The final stage of spermatogenesis is called spermiogenesis. Here the newly formed spermatids differentiate to become anatomically mature spermatozoa (or sperm). During spermiogenesis, the spermatid sheds excess cytoplasm and its nucleus elongates. A structure called the acrosome cap forms over the nucleus. The acrosome cap contains digestive enzymes that help penetrate the secondary oocyte for fertilization. The spermatids elongate and form a tail (flagellum) that is attached to a midpiece (or neck region) which contains mitochondria and a centriole.

30. Sperm leave their site of development (the seminiferous tubule) through a network of ducts that store and transport them. From the seminiferous tubules sperm first pass through the rete testis, a meshwork of interconnected channels within the testes that merge to form efferent ductules. Efferent ductules connect the rete testis to the epididymis. The sperm are stored here until they are fully mature and capable of being motile.

When sperm leave the epididymis, they enter the ductus deferens. The ductus deferens unites with the proximal

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part of the seminal vesicle to form the ejaculatory duct. The ejaculatory duct opens into the prostatic urethra.

The urethra transports sperm to the outside of the body.

31. The accessory glands include: the seminal vesicles, prostate gland, and bulbourethral glands. These glands secrete the components of seminal fluid, which will nourish the sperm as it travels through the reproductive tract.

32. Seminal fluid is a combination of the products of the accessory glands. Seminal fluid combines with sperm from the testes to make up semen.

33. The corpora cavernosa and corpus spongiosum are cylindrical, erectile bodies within the penis. The corpora cavernosa are paired and located dorsolaterally. Each terminates in the shaft of the penis. The corpus spongiosum is a single structure that contains the spongy urethra, and continues within the glans of the penis.

34. Erection occurs when blood enters erectile bodies within the penis and the erectile bodies become rigid.

Ejaculation is the process by which semen is expelled from the penis by rhythmic contractions of smooth muscle in the walls of the urethra.

35. Parasympathetic innervation (through the pelvic splanchnic nerves) is responsible for increased blood flow and thus erection of the penis, while sympathetic innervation from the lumbar splanchnic nerves causes rhythmic contractions of the smooth muscle in the wall of the urethra and is responsible for ejaculation.

36. The sex-determining region Y (SRY) gene is responsible for male phenotypic development.

37. The paramesonephric ducts persist in and form the female duct system. The mesonephric ducts form most of the male duct system.

38. In a developing female the paramesonephric ducts develop and differentiate. The caudal ends fuse and form the uterus and the superior part of the vagina. The cranial parts remain separate and form two uterine tubes.

39. Sustentacular cells secrete anti-Müllerian hormone (AMH), which inhibits the development of the paramesonephric ducts. The paramesonephric ducts degenerate and the mesonephric ducts begin to form the male duct system.

40. Production and circulation of testosterone causes the primitive external structures to differentiate into male structures.

41. The age at which menarche occurs may be affected by genetics, environmental factors, and overall health of the individual.

42. Gametes usually stop maturing in females by their 40s or 50s, and then menopause occurs. A reduction in hormone production accompanies menopause and causes some atrophy of reproductive organs and the breasts. Males do not experience the relatively abrupt change in reproductive system function experienced by females. Men generally do not stop producing gametes like women do following menopause. Additionally, while men experience a reduction in testosterone levels, this reduction is gradual and not as steep or sudden as the estrogen and progesterone drop seen in menopausal women.

Answers to “Do You Know the Basics?”

1. C Feedback: The clitoris and penis are homologues: both contain erectile tissue that stimulates feeling of arousal and sexual climax.

2. B Feedback: High levels of LH cause ovulation.

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3. C Feedback: The cervix is the inferior portion of the uterus that projects into the vagina.

4. C Feedback: An antrum first appears in the secondary follicle.

5. B Feedback: Interstitial cells produce androgens.

6. B Feedback: The testes produce spermatozoa. The components of seminal fluid are produced by accessory glands (seminal vesicles, prostate gland, and bulbourethral glands).

7. C Feedback: Spermatogenesis begins when spermatogonia divide by mitosis to form additional spermatogonia and primary spermatocytes.

8. A Feedback: The epididymis stores sperm until they are fully mature and capable of being motile.

9. D Feedback: High levels of estrogen cause the release of GnRH, which in turn stimulates the release of FSH and LH. 10. A Feedback: The paramesonephric ducts differentiate into the uterine tubes, uterus, and superior part of the vagina.

11. Male and female reproductive systems exhibit the following anatomic similarities: 1) Gonads are their primary reproductive organs (testes in the male and ovaries in the female); the gonads produce sex cells called gametes which unite at fertilization to initiate the formation of a new individual. (2) Gonads produce large amounts of sex hormones that affect maturation, development, and changes in the activity of the reproductive system organs.

(3) Both sexes have accessory reproductive organs with ducts to carry gametes away from the gonads (to the outside of the body in males, and toward the site of fertilization in females).

The anatomic homologues between the male and female reproductive systems include: Male organ homologue Testis

Female organ homologue Ovary

Glans of penis

Clitoris

Scrotum

Labia majora

Common function Produces gametes and sex hormones Contains erectile tissue / stimulates feelings of arousal and sexual climax Protect and cover some reproductive structures

12. The hypothalamus produces gonadotropin-releasing hormone (GnRH), which stimulates the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates follicular development. LH causes ovulation and subsequent development of the corpus luteum (a temporary endocrine gland formed by the remaining follicle cells in the ruptured mature follicle). The corpus luteum secretes estrogen and progesterone to stimulate and support the continuing buildup of the uterine lining and prepare the uterus for possible implantation of a fertilized oocyte.

13. Only primordial follicles are present at birth. It isn’t until puberty that primary follicles, secondary follicles and mature follicles begin to appear. A primary follicle contains a primary oocyte and one or more layers of cuboidal follicle (granulosa) cells. A secondary follicle contains a primary oocyte, many layers of follicle cells, and a small antrum. A mature follicle contains a secondary oocyte, many layers of follicle cells, and a large antrum. It is the mature follicle that will undergo ovulation.

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14. The uterine wall is composed of three concentric tunics: 1) the perimetrium (outer tunic) is a serosa that is continuous with the broad ligament (a sheet of peritoneum that supports the uterus and provides access for blood vessels), 2) the myometrium (middle tunic) is the thick uterine wall formed from three intertwined layers of smooth muscle, and 3) the endometrium (inner tunic) is an intricate mucosa composed of a simple columnar epithelium and an underlying lamina propria filled with compound tubular glands (uterine glands) that enlarge during the uterine cycle.

15. The events and phases that occur in both the ovarian cycle and the uterine cycle are shown in the following table (It is assumed that has a 28-day cycle).

Days 1-5 Ovarian cycle: Follicular phase - GnRH stimulates FSH and LH secretion. Ovarian follicles develop and produce estrogen.

Days 6-12 Ovarian cycle: Follicular phase estrogen and inhibin inhibit the hypothalamus and anterior pituitary, causing a drop in FSH. One follicle continues to mature and produce estrogen

Uterine cycle: Menstrual phase Functional layer of endometrium is shed.

Uterine cycle: Proliferative phase Functional layer of the endometrium is rebuilding.

Days 13-14 Ovarian cycle: Follicular phase The increase in estrogen above threshold stimulates the hypothalamus and anterior pituitary, causing an LH surge. The LH surge induces ovulation Uterine cycle: Proliferative phase Functional layer of the endometrium is rebuilding.

Days 15-28 Ovarian cycle: Luteal phase Corpus luteum forms and secretes large amounts of estrogen, progesterone, and inhibin. These inhibit GnRH, FSH, and LH secretion.

Uterine cycle: Secretory phase progesterone stimulates uterine lining growth. If the oocyte is not fertilized, the corpus luteum regresses and hormone levels drop.

16. 1) GnRH secreted by the hypothalamus stimulates the anterior pituitary to secrete FSH and LH. FSH stimulates sustentacular cells to secrete androgen-binding protein (ABP), which keeps testosterone levels high in the testis. 2) LH stimulates interstitial cells to secrete testosterone. 3) Testosterone stimulates spermatogenesis but inhibits GnRH secretion and reduces the anterior pituitary’s sensitivity to GnRH. 4) Rising sperm count levels cause sustentacular cells to secrete inhibin, which further inhibits FSH secretion.

5) Testosterone stimulates libido and development of secondary sex characteristics.

17. Sustentacular cells provide a protective environment for the developing sperm. They produce androgen-binding protein, which keeps testosterone levels high in the testis, and they release the hormone inhibin when sperm count is high. Inhibin inhibits FSH secretion and thus regulates sperm production.

18. All sperm develop from primordial germ (stem) cells called spermatogonia. 1) Diploid spermatogonia divide by mitosis to produce a new spermatogonium and a primary spermatocyte. 2) Primary spermatocytes (which are diploid) undergo meiosis I to produce two haploid secondary spermatocytes. 3) Secondary spermatocytes complete meiosis II to produce haploid spermatids. 4) Spermatids undergo spermiogenesis, where excess cytoplasm is shed, the nucleus elongates and an acrosome cap forms over the nucleus. The acrosome cap houses digestive enzymes to help penetrate the secondary oocyte for fertilization. As the spermatid elongates, a tail (flagellum) forms from microtubules within the cell. The tail is attached to a midpiece that contains mitochondria and a centriole.

19. Erectile bodies of the penis (two corpora cavernosa and one corpus spongiosum) are composed of a complex network of venous spaces surrounding a central artery. During sexual excitement, blood enters into the venous spaces, they become engorged and the erectile bodies become rigid. The rigid erectile bodies compress the veins that drain blood from the venous spaces; thus, blood remains within the erectile bodies until the sexual

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excitement ceases. Parasympathetic stimulation is responsible for increased blood flow and thus the erection of the penis. Ejaculation occurs at the end stage of an orgasm and is the process by which semen is expelled from the penis. It is due to rhythmic contraction of smooth muscle in the walls of the urethra and is the result of sympathetic innervations.

20. The paramesonephric ducts form most of the female duct system, including the uterine tube, uterus, and superior part of the vagina. The mesonephric ducts form most of the male duct system including the efferent ductules, epididymis, ductus deferens, and the seminal vesicle.

Answers to “Can You Apply What You’ve Learned?”

1. C Feedback: Spermatozoa are extremely sensitive to increases in temperature.

2. C Feedback: Ovulation occurs two weeks (or 10-14 days) prior to the next menstrual cycle. If Luisa has a 35 day cycle, then 14 days earlier would be day 21, and that would be when she ovulates.

3. A Feedback: LH stimulates interstitial cells to produce testosterone, and testosterone stimulates spermatogenesis.

4. B Feedback: Sexually transmitted infections are a leading cause of pelvic inflammatory disease in women, in which the reproductive organs become infected.

5. B Feedback: Follicle-stimulating hormone causes the development of primordial follicles.

Answers to “Can You Synthesize What You’ve Learned?”

1. Jennifer’s son has the characteristics of a child born with Trisomy 21 (Down syndrome). Increased maternal age is associated with an increased risk of having a child with trisomy 21, so Jennifer’s older than average age (44) may be associated with the child’s condition.

2. Two weeks following the previous menstruation is the optimum time for fertilization. This is the time at which estrogen levels peak, causing spike in the release of LH, and subsequent ovulation. Birth control pills contain progestins to inhibit the release of LH, thereby preventing ovulation.

3. Male and female external genitalia do not usually develop until week 20 of development.

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Chapter 29 Answers to “What Did You Learn?”

1. The pre-embryonic period is the first two weeks of development. It begins with fertilization and ends with implantation of the blastocyst in the uterus. The embryonic period is the third through the eighth week of development. Rudimentary versions of major organs appear. The fetal period is the remaining 30 weeks of development during which time the fetus continues to grow and organs increase in complexity.

2. Many sperm lack motility, leak out from the vagina or do not survive its acidic environment. Other sperm are prevented from reaching the secondary oocyte by the muscular contractions that cause “churning” in the uterus.

3. Fertilization involves three events: 1) sperm penetration of the corona radiata, 2) sperm release digestive enzymes from their acrosome (called the acrosome reaction), which permits the penetration of the zona pellucida and entry of the sperm nucleus into the secondary oocyte, and 3) fusion of the sperm and oocyte plasma membranes and nuclei.

4. The morula is the 16-cell stage.

5. The blastocyst has two distinct components: 1) the trophoblast is an outer ring of cells surrounding a fluid-filled cavity, and 2) the embryoblast, or inner cell mass, located within one side of the blastocyst.

6. The syncytiotrophoblast produces and releases a hormone called human chorionic gonadotropin (hCG). It signals the female reproductive system that fertilization and implantation have occurred. Thus the corpus luteum persists for another three months, producing large amounts of estrogen and progesterone that build and support the uterine lining. If the syncytiotrophoblast does not develop, then the uterine lining will degenerate, menstruation will follow and the pregnancy will not be maintained.

7. Significant levels of hCG are continuously produced and released to maintain the lining of the uterus only if implantation has occurred. The presence of hCG in blood or urine would therefore indicate pregnancy.

8. The bilaminar germinal disc consists of a hypoblast and an epiblast layer.

9. The yolk sac develops from the hypoblast, the amnion develops from the epiblast, and the chorion develops from both the cytotrophoblast cells and the syncytiotrophoblast.

10. The placenta is responsible for 1) the exchange of nutrients, waste products, and respiratory gases between the maternal and fetal blood, 2) transmission of maternal antibodies to the developing embryo or fetus, and 3) production of estrogen and progesterone to maintain and build the uterine lining 11. The cells of the epiblast migrate by the process called gastrulation to form the three primary germ layers (the ectoderm, mesoderm, and endoderm) from which all body tissues develop. The process begins with the formation of a primitive streak (a depression on the surface of the epiblast). Cells detach from the epiblast layer and migrate through the primitive streak (a process called invagination) to form a new layer of cells between the epiblast and hypoblast layers. This new, middle layer becomes the mesoderm. Cells remaining in the epiblast layer form the ectoderm while those cells in the hypoblast become the endoderm.

12. Cephalocaudal folding occurs in the head and tail regions of the embryo. The embryonic disc and amnion grow rapidly but the yolk sac does not grow at all. This differential growth causes the head and tail regions to fold on themselves. Transverse folding occurs when the left and right sides of the embryo curve and migrate toward the midline. The sides of the embryonic disc fuse in the midline to form a cylindrical embryo.

13. The ectoderm gives rise to the epidermis of the skin, the nervous tissue and sense organs, the pituitary gland, the adrenal medulla, the enamel of the teeth and the lens of the eye. The mesoderm gives rise to the dermis of the skin, the epithelial lining of the blood vessels, the lymph vessels and serous membranes, the muscle tissue, the connective tissue, the adrenal cortex, the heart, the kidneys and the ureters, the internal reproductive organs, and

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the spleen. The endoderm gives rise to the epithelial lining of the respiratory tract, the GI tract, the urinary tract, the reproductive tract, the tympanic cavity and the auditory tube, most of the liver, the gallbladder, the pancreas, the tonsils, the thyroid gland, the parathyroid glands, and the thymus.

14. During the embryonic period, the embryo is particularly sensitive to teratogens, substances that can cause birth defects or the death of the embryo. Many seemingly benign medications may act as teratogens.

15. The fetal period is characterized by maturation of tissues and organs, and rapid growth of the body. There are increases in both fetal length and weight.

16. 1) The differences between the first and second trimester include: the first trimester sees the development of the zygote into an embryo and then into an early fetus, while the second trimester is marked by growth of the fetus and expansion of maternal tissues. 2) The differences between the second and third trimester include: the second trimester is marked by growth of the fetus and expansion of maternal tissues, while the third trimester is a time of rapid fetal growth and weight gain in which the mother’s body prepares for labor and delivery.

17. Estrogen and progesterone suppress FSH and LH secretion, so the ovarian cycle and additional follicular development is arrested during the pregnancy. They also facilitate uterine development, mammary gland enlargement, and fetal growth.

18. CRH causes the release of aldosterone, which in turn causes the retention of fluids and an increase in blood volume during pregnancy. It is also believed to play a role in the length of pregnancy and the timing of childbirth.

HPL affects maternal nutrition, specifically the metabolism of fatty acid and leaving glucose reserves for the fetus.

It also inhibits the effects of insulin. Oxytocin is involved in uterine contractions and milk expulsion from mammary glands. Prolactin stimulates milk production in the breast and ensures that lactation occurs after birth.

19. The enlarged uterus pushes against the diaphragm and compresses many of the abdominopelvic organs, resulting in some nausea and gastrointestinal ailments, and also impinges on the bladder, causing more frequent urination.

20. Increasing levels of estrogen and progesterone during the first trimester cause the mammary glands to be tender and sore. The areolae and nipples darken in response to melanocyte-stimulating hormone, and mammary glandular tissue grows as additional acini develop under the influence of prolactin.

21. Increased levels of corticosteroids, estrogen, progesterone, and human placental lactogen result in increased insulin resistance in the pregnant mother, and in some cases can lead to gestational diabetes in the mother.

22. Weight gain during pregnancy is also due to 1) growth/enlargement of the fetus, placenta, breasts and uterus, and 2) fluid retention.

23. The cardiovascular system must distribute both respiratory gases and nutrients to the mother and growing fetus during pregnancy. Plasma volume increases by about 50%. Cardiac output increases up to 50% by week 6 of pregnancy (and peaks between weeks 24-28). Both heart rate and stroke volume must increase to support the need for increased cardiac output. Initially there may be an increase in blood pressure, but this drops in the second trimester because of decreases in peripheral vascular resistance and blood viscosity. In the third trimester, abdominal blood vessels are compressed by the increased size of the fetus and uterus, which may impair venous return from lower part of the body and result in the development of varicose veins, hemorrhoids, and/or edema.

24. Increased sensitivity of brainstem chemoreceptors to blood CO2 levels increases the rate of ventilation resulting in decrease in the concentration of blood CO2. Lower blood CO2 levels facilitate the diffusion of gases across the placenta. Increased ventilation and tidal volume levels cause an increase in consumption of oxygen to meet the oxygen demands of both mother and fetus.

25. Progesterone causes smooth muscle relaxation in the ureters that may cause dilation in ureters and renal pelvis.

Both this dilation and the increased urine volume may result in urine stasis (slowing or stopping). Additionally,

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compression of the ureter or kidney can result in problems with urine drainage. Collectively, these factors increase the risk of urinary tract infections (bacterial) during pregnancy.

26. Late in pregnancy estrogen levels increase to counteract the calming influence that progesterone has had on the uterine myometrium. The increased uterine myometrium sensitivity and the increasing levels of oxytocin (caused by estrogen) stimulate production of oxytocin receptors within the uterine myometrium. Collectively, these factors cause the myometrium to become more sensitive in the later stages of pregnancy and contractions begin to occur.

27. The five signs of false labor (known as Braxton-Hicks contractions) have the following characteristics: 1) They tend to be irregularly spaced and do not become more frequent as time passes. 2) They tend to be relatively weak, do not increase in intensity, and may stop entirely if the woman changes position or activity. 3) The pain from these contractions is usually limited to the lower abdomen and pelvic region. 4) The pain from the contractions may stop or change in response to movement. 5) They do not lead to the cervical changes seen in the three stages of labor.

28. The five signs of true labor have the following characteristics: 1) They tend to increase in frequency over time. 2) Contractions increase in intensity as labor progresses. 3) The pain from the contractions tends to radiate from the upper abdomen inferiorly to the lower back (or vice versa). 4) The pain from the contractions does not go away or change in response to movement. 5) The contractions facilitate cervical dilation and expulsion of the fetus and placenta.

29. True labor initiates a positive feedback mechanism that leads to the birth of the fetus. More intense uterine contractions result in the fetus’s head pushing against the cervix. This stimulates stretching and dilation of the cervix. Both the manual stretching of the cervix and the uterine contractions signal the hypothalamus to secrete more oxytocin. Additionally, uterine contractions stimulate the placenta to secrete more prostaglandins. Both result in more intense uterine contractions. True labor intensifies until the fetus is expelled.

30. The three stages of labor are: dilation, expulsion and placental. The dilation stage begins with the onset of regular uterine contractions and ends when the cervix is effaced and dilated to 10 centimeters in diameter. The expulsion stage begins with the complete dilation of the cervix and ends with the expulsion of the fetus from the mother’s body. The placental stage occurs after the baby is expelled: the uterus continues to contract to displace the placenta and remaining fetal membranes (called the afterbirth) from the uterine wall.

31. During the placental stage, uterine contractions prevent bleeding by compressing uterine blood vessels and expel remaining embryonic tissues. Fragments of placenta left in the uterus can lead to extensive bleeding or other postpartum complications.

32. When the neonate takes its first breath, the lungs must inflate and surfactant present in the alveoli must keep the alveoli open.

33. When the neonate takes its first breath, pulmonary resistance drops and the pulmonary arteries dilate. As a result, pressure on the right side of the heart decreases and the pressure is then greater on the left side of the heart 34. Because of the postpartum drop in estrogen and progesterone levels, cyclical hair loss returns.

Chemoreceptors become less sensitive to CO2 levels, thus lowering the respiratory rate, tidal volume, and pulmonary ventilation. Corticotropin-releasing hormone levels decline, possibly contributing to postpartum depression. Prolactin and oxytocin levels drop after birth, but since both are involved in lactation, there will be periodic surges in these hormone levels each time the baby nurses.

35. Excess fluids are lost postpartum through a combination of methods, including: the expulsion of amniotic fluid, increased urination, excessive bleeding and lochia, and profuse sweating.

36. Infant suckling stimulates mechanoreceptors in nipples to send sensory impulses to the hypothalamus. The hypothalamus produces oxytocin that is released from the posterior pituitary. Oxytocin then stimulates myoepithelial cells that surround mammary gland acini to contract. This causes the release of milk from acini.

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Simultaneously, stimulation of the breast causes a decrease in the production of dopamine in the hypothalamus, which triggers the release of prolactin from the anterior pituitary gland. This stimulates milk production.

37. Oxytocin facilitates shrinkage of the uterus postpartum by stimulating uterine contractions. Since breastfeeding stimulates oxytocin release, it also causes uterine contractions 38. We are crossing a Ww individual with a ww individual. Possibilities are: 50% Ww = heterozygous and 50% ww = homozygous dominant.

39. Codominant alleles appear to be equally dominant, and both are expressed in the phenotype.

Example = blood types A and B are codominant, so if both are received from the parents, then the progeny has and expresses both A and B. Incomplete dominance of a trait means that the individual does not express either the dominant phenotype or the recessive phenotype. What is expressed by the individual is incomplete dominance, a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a third phenotype in which the expressed physical trait is a combination of the dominant and recessive phenotypes.

40. All of her male children would be homozygous for the trait and would therefore be colorblind. All of her female children would be heterozygous for the trait and have normal vision.

41. Nutrition has a significant effect upon growth and development. Poor nutrition greatly decreases brain development and growth.

Answers to “Do You Know the Basics?”

1. D Feedback: The trophoblast is an outer ring of cells surrounding the blastocyst cavity that form the chorion.

2. B Feedback: Compaction of cells occurs during cleavage at the 8-cell stage to increase contact between cells to a maximum.

3. C Feedback: Migration of cells from the epiblast forms the three primary germ layers.

4. A Feedback: During implantation, the epiblast and hypoblast are formed from the embryoblast.

5. B Feedback: The endoderm, along with the mesoderm and ectoderm, form the three primary germ layers and so is not an extraembryonic membrane.

6. B Feedback: Blood pressure drops during the second trimester because of a decrease in peripheral vascular resistance that results from both a decrease in blood viscosity and a decreased sensitivity to the hormone angiotensin.

7. A Feedback: Within a few days after giving birth, estrogen and progesterone levels drop, because the uterine lining no longer needs to be maintained for pregnancy prolactin levels drop but may surge each time a baby nurses.

8. D Feedback: Since neither parent has freckles, they are both homozygous recessive for the trait. Therefore, they cannot have children with the dominant allele, thus the children will not develop freckles.

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9. D Feedback: Most human traits exhibit polygenic inheritance.

10. C Feedback: 50% of her gametes will carry the recessive allele.

11. Fertilization is the process by which two gametes (sex cells) fuse to form a new diploid cell containing genetic material derived from both parents. Fertilization involves three phases: 1) Corona Radiata Penetration: sperm that reach the secondary oocyte must use their motility to first penetrate the cell layer covering secondary oocyte. 2) Zona Pellucida Penetration: sperm release digestive enzymes from their acrosome (called the acrosome reaction) to penetrate the zona pellucida, allowing the nucleus of the sperm to enter the secondary oocyte (changes to the zona pellucida occur immediately, preventing entry by other sperm). 3) Fusion of Sperm and Oocyte Plasma Membranes and Nuclei: the sperm and oocyte plasma membranes fuse. Only the nucleus of the sperm enters the cytoplasm of the secondary oocyte. Thereafter, the secondary oocyte completes the second meiotic division and forms an ovum. The nucleus of the sperm and nucleus of the ovum are pronuclei (they are haploid). They fuse to form a single nucleus with a diploid number of chromosomes. This cell is called the zygote.

12. 1) Chordamesoderm: a midline group of mesodermal cells that form the notochord, which is the basis for central body axis and axial skeleton, and induces the formation of the neural tube. 2) The paraxial mesoderm gives rise to the axial skeleton, most muscle, most of the cartilage, the dermis, and connective tissues. 3) The intermediate mesoderm forms most of the kidneys, ureters, and the reproductive system. 4) The lateral plate mesoderm gives rise to the spleen, adrenal cortex, most of the components of the cardiovascular system, the serous membranes of the body cavities, and all the connective tissue components of the limbs. 5) The head mesenchyme forms connective tissues and musculature of the face.

13. During the embryonic period, the embryo is particularly sensitive to teratogens, substances that can cause birth defects of the death of the embryo. Because the embryonic period includes the formation of the primary germ layers and includes organogenesis, exposure to teratogens may result in the malformation of some or all organ systems.

14. The embryonic period is characterized by establishment of the three primary germ layers through the process of gastrulation. Subsequent interactions and rearrangements among the cells of the three layers prepare for the formation of specific tissues and organs, a process called organogenesis. The fetal period is characterized by maturation of tissues and organs, as well as rapid growth of the body.

15. 1) Human chorionic gonadotropin (hCG) is synthesized by the blastocyst to signal the female reproductive system to maintain and build the uterine lining; it remains high in the first trimester and then declines.

2) Estrogen and progesterone are produced in the second and third trimesters of pregnancy; they are responsible for the majority of effects on organ systems (integumentary, skeletal, reproductive, digestive, respiratory, and urinary) in the mother, they suppress FSH and LH secretion to prevent the ovarian cycle/additional follicular development, and they facilitate uterine enlargement, mammary gland development, and fetal growth. 3) Relaxin promotes blood vessel growth in the uterus. 4) Corticotropin-releasing hormone (CRH) causes release of aldosterone in the mother to promote fluid retention and overall blood volume. 5) Human chorionic thyrotropin (HCT) stimulates thyroid gland to increase the mother’s metabolic rate. 6) Human placental lactogen (HPL) affects how the pregnant woman metabolizes certain nutrients (i.e. - more fatty acids, so glucose is left for the fetus). 7) Prolactin stimulates milk production in mammary glands. 8) Oxytocin stimulates uterine contractions and expulsion of milk from mammary glands.

16. 1) The dilation stage begins with the onset of regular uterine contractions and ends when the cervix is effaced and dilated to 10 centimeters in diameter. 2) The expulsion stage begins with the complete dilation of the cervix and ends with the expulsion of the fetus from the mother’s body. 3) The placental stage occurs after the baby is expelled. During the placental stage, uterine contractions prevent bleeding by compressing uterine blood vessels, and they also expel remaining embryonic tissues.

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17. Infant suckling stimulates mechanoreceptors in nipples to send sensory impulses to the hypothalamus. The hypothalamus produces oxytocin which is released from the posterior pituitary. Oxytocin stimulates the mammary acinar cells to contract. Milk will continue to be released from the breast as long as the infant continues to nurse. Once the infant stops suckling, oxytocin levels drop and milk letdown stops. Simultaneously with nursing of the infant, dopamine release is inhibited by the hypothalamus. This inhibition of dopamine secretion stimulates the anterior pituitary to secrete large amounts of prolactin. This prolactin promotes new breast milk production.

18. The pregnant woman retains a great deal of fluid throughout pregnancy, including fluid in the amniotic sac and interstitial spaces, but most additional fluid is due to increased blood volume. Fluids are lost postpartum through: 1) the expulsion of amniotic fluid by the end of the first stage of labor, 2) release of lochia from the uterus - lochia is similar to a menstrual period in that blood and endometrial tissue are expelled from the uterus through the vagina, involving heavy bleeding in the first 5 days (but it may take 4 to 6 weeks to stop the flow), 3) increased urination for about the first week after delivery, and 4) profuse sweating for about the first week after delivery.

19. A dominant-recessive inheritance occurs when expression of the recessive allele is always masked by expression of the dominant allele (example: free earlobes (dominant) vs. attached earlobes (recessive)).

Incomplete dominance occurs when the phenotype of two heterozygous alleles is intermediate between the phenotypes of homozygous dominant or recessive alleles (example - the sickle cell trait: the individual does not have normal hemoglobin AND does not have sickle cell anemia, but some of their erythrocytes are inefficient and may fragment in the blood vessels. In other words, they express an inheritance that is in-between dominant and recessive). Complete dominance is shown when both alleles are expressed (example: an individual with an AB blood group phenotype expresses alleles inherited from both parents, which equals the A and B phenotype together). Polygenic inheritance involves the interaction of multiple genes and this is seen in the variation in height in the population.

20. Sex-linked traits are expressed by genes on the X or Y chromosomes. In order for a female to express a recessive X-linked trait, she must be homozygous for the recessive allele. A heterozygous female will be a carrier, and will not express the recessive phenotype. Males, however, can only carry one copy of the gene because they have only one X chromosome; therefore, they cannot have a dominant allele to mask the expression of the recessive allele. They cannot be heterozygous. An X-linked dominant will be expressed in either males or females. Males cannot be heterozygous for the trait. Females may be either homozygous dominant or heterozygous for an X-linked dominant trait.

Answers to “Can You Apply What You’ve Learned?”

1. D Feedback: Heart rate is usually slightly elevated during pregnancy to accommodate the increased blood volume. Increased insulin resistance results in glucose remaining longer in the blood to provide availability to the fetus. Urine content will also vary due to the presence of waste from the fetus as well as maternal waste.

Finally, weight gain of up to 20 pounds is not uncommon during pregnancy.

2. A Feedback: The crown-rump length of a fetus at 20 weeks should be approximately 19 centimeters.

3. B Feedback: Uterine contractions result in the fetus’s head pushing against the cervix. This manual stretching of the cervix and uterine contractions both signal the hypothalamus to secrete more oxytocin, which stimulates stronger contractions.

4. A Feedback: Oxytocin stimulates the release of milk from breast acini and causes uterine contractions. Infant suckling stimulates mechanoreceptors in nipples to send sensory impulses to the hypothalamus. The

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hypothalamus releases oxytocin through the posterior pituitary, which then has its effect in both the breast tissue and the myometrium of the uterus.

5. C Feedback: Males receive an X chromosome from their mother and a Y chromosome from their father. Therefore, a male with an X-linked trait inherited it from his mother. Since it is a recessive trait, a heterozygous mother is a carrier for the allele. She does express the recessive phenotype because it is masked by the dominant allele.

Answers to “Can You Synthesize What You’ve Learned?”

1. Since most differentiation and organogenesis occurs during the embryonic period of development, that is the point of particular sensitivity and potential exposure to teratogens.

2. Alcohol is a powerful teratogen. Since most differentiation occurs during the first trimester of development, exposure to alcohol can be damaging to the embryo.

3. If their father was homozygous for the autosomal dominant disorder, they will both have inherited one dominant allele, and will therefore have a 100% chance of getting the disorder. If the father was heterozygous, then they each would have a 50% chance of acquiring the dominant allele and subsequently getting the disorder. Since they each have a 50% chance of acquiring the dominant allele from their father, there is a 25% probability that they will both get the disorder since their mother was normal.

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