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Lecture

PHGY210- Lecture 26- Dr. Wechsler.docx

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Department
Physiology
Course
PHGY 210
Professor
Ann Wechsler
Semester
Winter

Description
Lecture 26- Wednesday, March 10 , 2010th Lower Esophageal Sphincter No visible enlargement of curcular muscle. Anatomically insignificant, functionally very important. Closure= myogenic Relaxation= Neurogenic- Local release of NANC PICTURE AT SLIDE 56 LES – lowermost 4 cm of the esophagus, straddling the diaphragm. When swallowing is not occurring, the sphincter is in a state of tone, and its walls are in firm apposition. The tone is largely myogenic, but under neural and hormonal influences. Relaxation of the LES is reflex, initiated during swallowing and mediated by vagal efferent fibres releasing ACh, which activate inhibitory enteric neurons which release a NANC transmitter, causing muscle tone decrease. Note: the LES has an intrathoracic segment (subject to –ve pressure) and an intraabdominal segment (subject to +ve pressure), and the pressures within these segments vary with phases of respiration. The presence of an intraabdominal segment of the LES assists the sphincter in maintaining an effective barrier between the stomach and esophagus: if the intraabdominal pressure is raised, the pressure of both the terminal segment and the intragastric contents is raised equally, so that there is no effective change in the gradient of pressure between stomach and esophagus. PICTURE AT SLIDE 59 LES Characteristics 1. INTRINSIC PHYSIOLOGIC SPHINCTER 2. Assisted by presence of an INTRAABDOMINAL SEGMENT Incompetent LES- sphincter fails to close “Heartburn” (PYROSIS): burning sensation, radiating upwards in the chest towards the neck, due to acid reflux into esophagus PICTURE IN SLIDE 62 Motor Functions of the Stomach 1. Temporary Storage- 1-3 L of contents in the course of a single meal 2. Physical Disruption and Mixing of Contents- Semi Liquid Consistency= CHYME 3. Propulsion into Duodenum- Regulated Proximal Region- Thin walled Distal Region- Thick walled Large doses of Gastrin will have an effect on LES, but only in very large doses. Therefore Gastrin does not play a role in modulation of LES. Progesterone has been known to relax the sphincter. Accomodation of a Meal Intergastric pressure= -5 mmHg When you take in a meal, only the proximal region expands. Increase in volume not accompanied by any significant increase in intragastic pressure called Receptive Relaxation. This receptive relaxation is restricted to the proximal stomach only. Receptive Relaxation Receptive Relaxation is part of the deglutition r
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