Which causes antral gastrin release?
Correct Answer: Antral distension
Description: Gastrin is produced by cells called G cells in the antral poion of the gastric mucosa.G cells are flask-shaped, with a broad base containing many gastrin granules and a narrow apex that reaches the mucosal surface. Microvilli project from the apical end into the lumen. Receptors mediating gastrin responses to changes in gastric contents are present on the microvilli. Other cells in the gastrointestinal tract that secrete hormones have a similar morphology. Gastrin is typical of a number of polypeptide hormones in that it shows both microheterogeneity and microheterogeneity. Microheterogeneity refers to the occurrence in tissues and body fluids of peptide chains of various lengths; microheterogeneity refers to differences in molecular structure due to derivatization of single amino acid residues. preprogastrin is processed into fragments of various sizes. Three main fragments contain 34, 17, and 14 amino acid residues. All have the same carboxyl terminal configuration. In large doses, gastrin has a variety of actions, but its principal physiologic actions are stimulation of gastric acid and pepsin secretion and stimulation of the growth of the mucosa of the stomach and small and large intestines (trophic action). Gastrin secretion is affected by the contents of the stomach, the rate of discharge of the vagus nerves, and bloodborne factors. Atropine does not inhibit the gastrin response to a test meal in humans, because the transmitter secreted by the postganglionic vagal fibers that innervate the G cells is gastrin-releasing polypeptide rather than acetylcholine. Gastrin secretion is also increased by the presence of the products of protein digestion in the stomach, paicularly amino acids, which act directly on the G cells. Phenylalanine and tryptophan are paicularly effective. The acid in the antrum inhibits gastrin secretion, paly by a direct action on G cells and paly by release of somatostatin, a relatively potent inhibitor of gastric secretion. The effect of acid is the basis of a negative feedback loop regulating gastrin secretion. Increased secretion of the hormone increases acid secretion, but the acid then feeds back to inhibit fuher gastrin secretion. In conditions such as pernicious anemia in which the acid-secreting cells of the stomach are damaged, gastrin secretion is chronically elevated.REF: GANONG&;S REVIEW OF MEDICAL PHYSIOLOGY, KIM BARRETT, HEDDWEN BROOKS, SCOTT BOITANO, SUSAN BARMANTWENTY THIRD EDITIONPAGE NO:443
Category:
Physiology
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