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Cephalic, Oral and Esophageal Phases of a response to a meal


Objectives • Identify cephalic, oral and esophageal phases • What is salivary secretion? • What are the ionic mechanisms of salivary secretion? • What is the swallowing reflex? • What is the motor activity during esophageal phase?


Composition of Generic Ham Sandwich • Bread- whole wheat: g/Slice Fat 2g Na+ 160 mg Carbohydrates 21g “sugars” 2g • Ham- sliced g/2slices fat 1.5g Na+ 640 mg Protein 9g CHO 1g • Yellow mustard g/5ml Na+ 60 mg Protein 0.2g


What is digested and absorbed from the Ham sandwich? • Carbohydrates: Complex (to be hydrolyzed into monomeric sugar: 22 g • D-glucose & Fructose: 2 g • Protein: To be hydrolyzed into free amino acids: 9.2 g • Fat: 3.5 g

Total Na+ : 760 mg


Cephalic phase • Activation of GI tract in readiness for a meal • Stimuli – cognitive • Olfactory, visual • Auditory- classic conditioning exps of Pavlov • Pairing auditory stimulus to presentation of food; auditory stimulus alone-salivary secretion


Cephalic phase (cont’d) • Activation of dorsal motor nucleus in brainstem • Region where cells bodies of Vagal preganglionic neurons arise • Activation of the nucleus leads to increased activity in efferent fibers passing to GI tract of vagus nerve • Efferent fibers activate postganglionic motor neurons.


Cephalic phase (cont’d) • Increased parasympathetic outflow enhances Salivary secretion Gastric acid secretion Pancreatic enzyme secretion Gallbladder contraction Relaxation of sphincter of Oddi (the sphincter between bile duct & duodenum


Cephalic phase (cont’d) • Salivary response is mediated by the 9 th cranial nerve • Remaining responses via vagus nerve


General structure of Salivary gland


Saliva • Produced by 3 pairs of salivary glands • 99.5% H20, 0.5% electrolytes and protein (amylase, mucin or mucus, [a glycoprotein] lysozyme, lipase) • Function: Begins digestion of carbohydrates Mucin provides lubrication Antibacterial - lysozyme


Salivary secretion as f(x) flow rate


Acinar secretion • Primary secretion by acinar cells in the end pieces & modified by duct cells as saliva passes through ducts • 1O secretion is isotonic (comparable to plasma) • Secretion driven by Ca2+-dependent signaling, opens Cl- channels in apical membrane (Na+, H20 follow)


Ion transport for secretion of amylase and electrolytes from salivary acinar cells


Acinar secretion (cont’d) • Water movement is through Aquaporin 5 water channels • Duct cells reabsorb Na+ and Cl- and secrete K+ and HCO3 into lumen • Final ductal secretion is alkaline and hypotonic • HCO3 secretion directly stimulated by hormones


Two-stage model of salivary secretion


Acinar secretion (cont’d) • Water movement is through Aquaporin 5 water channels • Duct cells reabsorb Na+ and Cl- and secrete K+ and HCO3 into lumen • Final ductal secretion is alkaline and hypotonic • HCO3 secretion directly stimulated by hormones


Metabolism and blood flow of salivary glands • Max rate in humans= 1ml/min/g of gland • Glands producing their own wt in saliva/min • High rate of metab & blood flow- both proportional to rate of saliva production • Blood flow to secreting salivary gland is 10X equal mass of contracting skeletal muscle • Stim of parasympathetic nerves increases blood flow by dilating vasculature of glands • VIP and acetylcholine from parasym-vasodil


Control of Salivary Secretion


Swallowing • Motility associated with pharynx and esophagus • Sequentially programmed all-or-none response • Most complex reflex in the body • Initiated voluntarily but can’t be stopped once begun


Timing of motor events in pharynx and upper esophageal sphincter during a swallow


Swallowing (cont’d) • Tip of tongue presses palate • Moves bolus upward and backward • Bolus forced into pharynx- where it activates touch receptors that initiate reflex • Pharyngeal phase (< 1 sec) • Soft palate is pulled upward and palatopharyngeal folds move inward toward one another.


More swallowing • These movements prevent reflux of food into nasopharynx and open a narrow passage (so bolus moves into pharynx) • Vocal chords pulled together and larynx is moved forward and upward against epiglottis • Prevents food entering trachea and opens UES


Protection of airway: UES and LES


More swallowing • These movements prevent reflux of food into nasopharynx and open a narrow passage (so bolus moves into pharynx) • Vocal chords pulled together and larynx is moved forward and upward against epiglottis • Prevents food entering trachea and opens UES


Changes in pressure along esophagus during swallowing


Pharyngeal stimulation induces neural reflex to relax LES


Swallowing • The UES relaxes to receive the bolus • The superior constrictor muscles of pharynx contract to force bolus deeply into pharynx • Peristaltic wave is initiated with contraction of pharyngeal superior constrictor muscles • Wave moves toward esophagus • this forces bolus through relaxed UES • Reflex action causes UES to constrict


Esophageal Phase • UES and LES serve two main functions • Propel bolus away from mouth • Protect airway during swallowing and esophagus from acid secretion of stomach • Stim of pharynx by bolus produces reflex relaxation of LES and most proximal part of stomach


Peristalsis in the Esophagus


Definition Homeostasis Homeo: “the same” stasis: “to stand or stay” Maintenance of a relatively stable internal environment.


Alterations in LES- bad • Failure of the LES to constrict after swallowing can lead to gastroesophageal reflux disease (GERD) • Commonly known as heartburn or indigestion • Pain fibers in esophagus activated by acid from stomach • Continual reflux leads to esophageal erosion= treated by acid inhibitors


Oropharyngeal Stage of Swallowing


Readings • Sherwood/Kell/Ward: Human Physiology:From Cells to Systems Chpt 14. • Silverthorn Chapter 21 p 689-698, 708711.

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