De La Salle University BIOLOGY SHS General Biology 2 (Lecture) Notes 2. Complete 133 Pages

General Biology 2 (Lecture) Notes 2 Table of Contents Lecture 11: The Integumentary System Lecture 12: The Musculoskeletal System Lecture 13: The Digestive System Lecture 14: The Respiratory Syst em Lecture 15: The Circulatory System Lecture 16: The Excretory System Lecture 17: The Reproductive System Lecture 18: The Nervous System Review #3 Lecture 19: The Endocrine SystemLecture 11: The Integumentary System Meeting 9 (04/15/2021) The Integumentary System ● Refers to the body covering or mostly the skin, the largest organ ● Functions ○ Protects the underlying organs and tissues ○ Maintains body temperature (thermoregulation) ○ Synthesizes Vitamin D2 ○ Stores lipids ○ Detects touch, pressure, pain, and temperature (sensory) ○ Excretes salt, water, and organic wastes ○ Protects the body against infection ● Mammalian skin and its modifications distinguish the mammals as a group ● Mammals’ body is mostly covered with hair ○ Some with reduced coverage ○ Presence of sweat, scent, and sebaceous glands ○ Underneath the skin is a thick layer of fat or adipocytes ● The integumentary system protects your body against infection and extreme temperatures, maintains your balance of fluids, and even synthesizes vitamin D for your own personal use. 2 Layers of the Integument ● For other literature, there are 3 layers of the integument. However, for the lecture, only 2 will be considered. ● Epidermis ○ The layer of skin that we always see ○ On top of the epidermis layer, there are stratified squamous epithelium cells that can be found ○ Thinner ○ Protected by hair ○ Some areas become thickened with keratin ■ Keratin - fibrous protein that also constitute the nails, claws, hooves, and hair ● Dermis ○ Where most biological processes take place ○ Mainly made up of connective tissues ○ Location of nerve endings, blood vessels, and follicles ○ If there is a wound and bleeding ensues, it means the dermis was hit ● Hypodermis ○ Also known as the subcutaneous layer ○ Where fat cells are locatedFigure 11.1. The epidermis and dermis Layers of the Epidermis ● At the top, there are dead cells flaking off at the skin surface. These cells will regenerate. ● The deeper the layer, the younger the cells. ● As the cells go farther and farther from the blood, they become older. ● Stratum corneum ○ Outermost keratinized layer ○ Dry, dead layer helps prevent penetration of microbes and dehydration ○ First line of defense against invaders ○ Provides protection against abrasion for the more delicate, underlying layers ● Stratum lucidum ○ Very thin layer ○ Only appears in certain parts of the body ■ Found only in thick skin of palms, soles, and digits ● Stratum granulosum ○ Grainy in appearance ○ Generate large amounts of keratin ○ Has granular cells ● Stratum spinosum ○ Spiny in appearance due to protruding cell processes that joins the cells via the desmosome ○ The thickest part ○ It is referred to as spinosum because when it is observed under the microscope, it resembles a spine ● Stratum basale ○ Also known as stratum germinativum ■ The germinative layer ■ Composed of germinative (or basal) keratinocytes ■ These cells are actively dividing to provide new cells to replenish lost skin from normal shedding○ The deepest layer ○ Comprised of single layers of cells ○ These are the youngest cells that are being produced. Figure 11.2. The layers of the epidermis Figure 11.3. The layers of the epidermis under a microscopeFigure 11.4. The cells of the layers of the epidermis Cell of the Layers of the Epidermis ● Lamellar granules ○ Make up the stratum granulosum. ○ These granules have a role in keratinization and maintaining the barrier functions of the skin. ○ The lamellar granules contain several types of lipids (ceramides, cholesterol, fatty acids) and hydrolytic enzymes including proteases, acid phosphatases, lipases and glycosidases ● Keratinocytes ○ They are the primary type of cell found in the epidermis, the outermost layer of the skin ○ The main purpose of these keratin-producing cells is to preserve against microbial, viral, fungal and parasitic invasion; to protect against UV radiation; and to minimize heat, solute and water loss. ● Langerhans cells ○ They are part of the immune system, which serve as the defense against foreign invaders ○ They help to protect the body by keeping dangerous microbes from entering your body. ○ Langerhans cells do this in two very different ways: by protecting your skin from infection and also by stimulating allergic reactions. ● Melanocytes ○ Produce melanin ○ Melanin is a dark pigment primarily responsible for skin color ● Merkel cells ○ Make up the stratum basale○ Connected to the nervous system ○ Receives stimulus ○ These cells are thought to function as slowly adapting mechanoreceptors that mediate the senses of touch and hair movement. Parts of the Dermis Figure 11.5. The parts of the dermis ● Hair ○ Aka pili ○ Characteristics of mammals ■ Reduced on humans ■ Exists as few bristles on whales ○ Hair follicle ■ Epidermal structure ■ Lies in the dermis ■ Where hair is actively growing ○ Each hair strand has blood vessels for nutrition ○ Hair grows continuously ■ Rapid proliferation of cells in the follicle ■ Cells in the hair shaft are pushed upwards away from their source of nourishment ● Accumulate keratin and die ○ Hair stops at a certain length ■ Remains in the follicle until new growth pushes it out ○ 2 types of hair in mammals ■ Under hair ● Aka undercoat● Dense and soft ● For insulation ■ Guard hair ● Course and longer ● Protect against wearing ● Provide coloration ● Under water, they become wet and adhere to each other ○ Stages of Hair Growth ■ Anagen - growing phase ● Lasts an average of 3-7 years ● Longest phase ● Transitional phase ■ Catagen - stopped growing, keratinized fully ■ Telogen - dying and molting ■ Extra: Exogen - phase wherein hair falls out ○ 3 Layers of Hair ■ Medulla ● Center of the hair ■ Cortex ● With pigment granules lie outside the medulla ■ Cuticle ● Outermost layer ● Made up of imbricated scales ● Conditioners smoothen the ragged cuticles ○ In most animals, there is periodic molting of the entire coat. ■ Foxes and seal ● Once every summer ■ Most mammals ● Molts twice ● Winter coat ○ White ○ For camouflage ● Summer coat ○ Brown ○ Different mammals have unique hair structures ■ Deer ● Brittle hair is deficient of cortex ■ Wolverine ● Hollow, air-filled airs are deficient of medulla ■ Rabbits ● Scaled to interlock when pressed together ■ Sheep ● Curly hair grows from curved follicles ○ Structural and Functional Adaptation■ Patterns ● Spots, stripes, salt-and-pepper ● Disruptive ● Conceal the animals ● Arrector pili muscle - allows goosebumps or for hair to stand straight when in shock, afraid, or cold. ● Papilla - are specialized mesenchymal cells that exist in the dermal papilla located at the bottom of hair follicles. These cells play pivotal roles in hair formation, growth, and cycling Show Less