A hormone produced by G cells in the lateral walls of the antrum gastric mucosa.
G cells are flasked-shape cells containing gastrin granules, and a narrow apical mucosal surface with microvilli.
The microvilli have mediating receptors that respond to gastric content changes.
G cells produce gastrin in response to stomach stretching occurring after food enters it, and also after stomach exposure to protein.
Also found in pancreatic islets in utero.
Gastrinomas, gastrin producing tumors, occur in the pancreas.
Gastrin is found in the anterior and intermediate lobes of the pituitary gland, the hypothalamus, medulla, and vagus and sciatica nerves.
Gastrin has both macro and micro heterogeneity, and the various gastrins or inactivated primarily in the kidney and small intestine.
Its principal physiologic actions are stimulation of gastric acid and pepsin secretion and stimulation of the growth of stomach, small and large intestine mucosa.
Gastrin is an endocrine hormone and therefore enters the bloodstream and eventually returns to the stomach where it stimulates parietal cells to produce hydrochloric acid (HCl) and Intrinsic factor (IF).
May stimulate gastric motility.
Stimulates insulin secretion after protein intake, but not after a carbohydrate meal.
Functions of gastrin from the pituitary gland and peripheral nerves are unknown.
Secretion is affected by stomach contents, vagal nerve activity, and blood-borne factors.
Secretion is increased by the products of protein digestion in the stomach, particularly amino acids, which act directly upon G cells.
Acid in the antrum inhibits gastrin secretion, by direct action on G cells and by release of somatostatin, a relatively potent inhibitor of gastric secretion.
Acid acts as a negative feedback loop regulating gastrin secretion: increased secretion of gastric and increases acid secretion, and the acid then feeds back to inhibit further gastrin secretion.
Secretion is chronically elevated in pernicious anemia, as acid secreting cells of the stomach are damaged.