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PHGY210- Lecture 25- Dr. Wechsler.docx

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PHGY 210
Ann Wechsler

Lecture 25- Monday, March 8 , 2010h GIT Structure, Functions, Regulation -Motility: There are sertain regions in which the musculature is striated (eg the pharynx, upper 1/3 of the esophagus, external anal sphincter, mouth). From below the upper 1/3 of the esophagus to the internal anal sphincter is smooth muscle enteric innervation. Propulsion (Flow) in the Gut: Based on:  Establishment of gradients of pressure results from the coordinated contraction of the muscular elements of the wall of the GIT (mostly smooth muscle) o Segmentation: rings of contraction which divide the gut into sausage like sections. Very effectice mixing movement mixing contents back and forth. o Peristalsis: analogy: taking a tube of toothpaste, squeezing it down so that toothpaste comes out of the tube you are acting like a peristaltic wave.  Variations in resistance o Normally very little or no resistance. o Used to be thought that sphincters regulate the flow of contents through tubes. One way valves control movement from one organ to another, close to prevent reflux back into the organ it came from. -Normally, flow is slow, aboral and meets little/no resistance. Phases of Deglutition (swallowing) pages 590-593 -Is accomplished through a complex series of highly coordinated muscular movements aimed at building up pressure, temporarily sealing off of compartments to prevent dissipation of pressure, and decreasing resistance. -All of deglutition occurs with the mass of food you ingested moving from the oral cavity into the stomach.  Oral phase  pharyngeal phase  esophageal phase Oral Phase: -Transport of bolus (masticated, insalivated mass of food) from anterior to posterior portion of mouth. This involves a series of reflexes coordinated in DEGLUTITION CENTRE in medulla oblongata -Transport from anterior mouth to pharynx. -Voluntary control. Cortical vs Medullary Centres see picture above -“Voluntary” (ability to initiate) -Deglutition Center (“involuntary” reflexes coordinate movement) -Cortical Center to Medullary Center Pharyngeal Phase: Under involuntary control, consists of a) a series of protective reflexes, initiated by stimulation of afferent fibres in the pharynx, organized in Deglutition Centre, closing off nasal, oral, and laryngeal cavities, preventing misdirection of the bolus. Simultaneously, respiration is briefly inhibited. b) transfer to esophagus, as pharyngeal muscles contract and Upper Esophageal Sphincter relaxes. -Where the respiratory and digestive systems cross. -What needs to happen:  Passages into the nose, mouth, trachea blocked  Apnea  added measure of safety, stop breathing.  UES (upper esophageal sphincter) relaxes  Pharynx muscles contract  Epiglottis covering the glottis  secondary process, not that important Upper Esophageal Sphincter -Corresponds to muscle- Cricopharyngeus. Must be activated neurally by the Somatic Fibres of the Vagus Nerve are what innervates it. -CLOSURE of the sphinct
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