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Lecture 20

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McGill University
PHGY 210
Ann Wechsler

Lecture 20 Vomiting: No anti-peristaltic waves in the upper tracks. Decrease resistance to upward flow and increase pressure in the stomach. The distal stomach (including sphincter) goes into spasm, this forces food up. The proximal stomach and esophagus are completely passive, no movement. The increase in the pressure is due to the descent of the diaphragm and the contraction of the stomach. Vomiting is then a result of the diaphragm and the abdominal muscles to increase inner pressure while the GIT is mostly passive. Regulation of Vomiting: pharyngeal stimulation, distension/irritation, cardiac ischemia, pain, motion sickness, psychogenic factors and even biochemistry of ingested items could trigger vomiting. The afferent impulses go to the medulla vomiting centre. This creates an efferent output. No vomiting without afferent going and efferent leaving the medulla. Tachycardia, then bradycardia, clammy hands due to vasoconstriction, this all leads to nausea, which then leads to small amount of retching. This is because the constrictions are not synchronized. Retching is the exchange of food between stomach and esophagus. Toxic materials act on an intermediate centre, known as the CTZ, the chemoreceptor trigger zone, which is outside the blood-brain barrier. However, this still requires the vomiting centre to cause a response. Upper Small Intestine Neutralization, osmotic equilibration, digestion and absorption. The small intestine is in reality the site where effective mixing takes place, slowly propelled while digestive juices are used on the chyme. Frequency of contraction is governed by the BER (ECA), the basic electrical rhythm. The ERA spikes are once again phase locked and are initiated by stretching of Ach. The intestinal BER is not uniform in the entirety of the intestine, it decreases from the proximal to the distal intestine. From 12 per minute in the duodenum to 8 per minute in the ileum. The smooth muscle responds more in the proximal region of the small intestine than in the distal region. The thickness of the small intestine is greater in the proximal region than in the distal region. The most common type of contraction in the s.i. after a meal is segmentation. This creates multiple ring
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