PHGY 210 Lecture Notes - Lecture 5: Spasm, Duodenum, Digestion

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Published on 27 Nov 2015
School
McGill University
Department
Physiology
Course
PHGY 210
Professor
Phgy 210
March 18, 2015
Digestion Lecture 5
Vomiting
Vomiting results from the action of the diaphragm and abdominal muscles to increase
intraabdominal pressure - GIT is mostly passive
"anti-peristaltic" waves moving upwards
Upper gastrointestinal tract (upper stomach, esophagus) are free of contractions
Distal stomach and upper duodenum are contracted in spasm
If there is an increase in intraabdominal pressure, contents will move in the path of least
resistance, i.e. upwards
Diaphragm is lowered, pressure is increased (could cause projectile vomiting)
Regulation of vomiting
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Phgy 210
March 18, 2015
Impulses from vomiting can originate anywhere in the body
But they end up in the vomiting center
There is a widespread autonomic discharge that causes nausea, retching, and emesis - the three
stages of vomiting
o Emesis is the actual expulsion of contents of upper GIT: individual takes a deep breath,
closes glottis, contracts abdominal muscles, exerting pressure on gastric contents
o Emesis is completed with the reversal of thoracic pressures from -ve to +ve, as the
diaphragm is displaced upwards, forcing esophageal contents to be expelled through the
mouth
At the same time, upper GI tract relaxes, and pyloric antrum and duodenum go to spasm
There is contraction of abdominal muscles and diaphragm
Vomiting response to circulating emetic agents
o e.g. bacterial toxins
o They do not act directly on the vomiting center, they work on the chemoreceptor trigger
zone (CTZ) which is distinct from the vomiting center
o It lies outside the blood-brain barrier
o CTZ is capable of responding to these agents and it will send impulses to the vomiting center
o If CTZ is destroyed but vomiting center is intact, can no longer respond to these agents
o Destroying the vomiting center but not the CTZ will not give rise to any vomiting
Upper Small Intestine
1. Neutralization
o Chyme can be hypotonic, isotonic, hypertonic
o Becomes isotonic by the end of the duodenum
o Remains isotonic for the rest of the transport in the intestinal tract
2. Osmotic equilibration
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Document Summary

Vomiting results from the action of the diaphragm and abdominal muscles to increase intraabdominal pressure - git is mostly passive. Upper gastrointestinal tract (upper stomach, esophagus) are free of contractions. Distal stomach and upper duodenum are contracted in spasm. If there is an increase in intraabdominal pressure, contents will move in the path of least resistance, i. e. upwards. Diaphragm is lowered, pressure is increased (could cause projectile vomiting) Impulses from vomiting can originate anywhere in the body. But they end up in the vomiting center. At the same time, upper gi tract relaxes, and pyloric antrum and duodenum go to spasm. There is contraction of abdominal muscles and diaphragm. Vomiting response to circulating emetic agents: e. g. bacterial toxins, they do not act directly on the vomiting center, they work on the chemoreceptor trigger zone (ctz) which is distinct from the vomiting center.

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