Gastric secretion is brought about by duodenal distension and the presence of protein digestion products, i.e. peptides and amino acids. The presence of acid, fat digestion products and hypertonicity in the duodenum and proximal jejunum inhibit gastric acid secretion and gastric emptying. Acid in the duodenum causes secretin release, which inhibits gastrin release by G cells and inhibits the response of parietal cells to gastrin. Fatty acids in the duodenum release two hormones, cholecystokinin (CCK) and gastric inhibitory peptide (GIP). Cholecystokinin inhibits acid secretion by parietal cells. Gastric inhibitory pep-tide suppresses gastrin release and also directly inhibits acid secretion by parietal cells.
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