Phgy 210 – Gastric System 5
The reverse gradients of pressure are not created by anti-peristaltic waves or
contractile movement. The vomiting results from the action of the diaphragm and
abdominal muscles to increase intraabdominal pressure – GIT is mostly passive.
How is it regulated? Regulation of these reflexes takes place in the vomiting
center, on the flour of the 4
ventricle. Taking it off, no vomiting will ever occur.
Impulses occur from anywhere in the body (distension, irritation of the GIT, UG,
pain, biochemical disequlibrium, psychogenic factors, unequal stimulation of
labyrinth, ie motion sickness for instance). The output, however, is fairly
Widespread autonomic discharge + nausea, also retching
Dilated pupils, cutaneous BV constriction (pale skin), sweating, salivation,
These precede and accompany the expulsion of contents.
EMESIS : Results in the relaxation of the GI tract + spasm of the pyloric
antrum and duodenum, AND contraction of abdominal muscles and
The emetic response can be triggered by chemicals and/or bacteria. They don’t
act directly on the emetic response, however, because of the blood/brain barrier.
The CTZ, however, lies outside the bb barrier and can be stimulated by agents
such as drugs, chemicals and toxins. It can sense these agents and does not
induce vomiting directly, except by sending impulses to the fourth ventricle, then