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Pepsin / ˈ p ɛ p s ɪ n / is an endopeptidase that breaks down proteins into smaller peptides and amino acids. It is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Pepsin is an aspartic protease, using a catalytic aspartate in its active site. [2]
Also, the secretion of secretin is increased by the products of protein digestion bathing the mucosa of the upper small intestine. [22] Secretin release is inhibited by H 2 antagonists, which reduce gastric acid secretion. As a result, if the pH in the duodenum increases above 4.5, secretin cannot be released. [23]
Principal known actions Bombesin: Throughout the gut and pancreas: Stimulates release of cholecystokinin (CCK) and gastrin Calcitonin gene-related peptide: Enteric nerves: Unclear Chromogranin A: Neuroendocrine cells: Secretory protein Enkephalins: Stomach, duodenum: Opiate-like actions Enteroglucagon: Small intestine, pancreas: Inhibits ...
Pepsinogen is a precursor enzyme produced by the gastric chief cells, and gastric acid activates this to the enzyme pepsin which begins the digestion of proteins. As these two chemicals would damage the stomach wall, mucus is secreted by innumerable gastric glands in the stomach, to provide a slimy protective layer against the damaging effects ...
This type of cell also secretes gastric lipase enzymes, which help digest triglycerides into free fatty acids and di- and mono-glycerides. [3] There is also evidence that the gastric chief cell secretes leptin in response to the presence of food in the stomach. Leptin has been found in the pepsinogen granules of chief cells. [4]
Cholecystokinin (CCK) is a unique peptide released by the duodenal "I cells" in response to chyme containing high fat or protein content. Unlike secretin, which is an endocrine hormone, CCK actually works via stimulation of a neuronal circuit, the end-result of which is stimulation of the acinar cells to release their content. [ 14 ]
Prorennin is secreted in young mammals (childhood stage). It is not secreted in adult mammals. Chief cells also produce small amounts of gastric lipase. Gastric lipase contributes little to digestion of fat. Parietal cells ("parietal" means "relating to a wall"), also known as oxyntic cells are most numerous on the side walls of the gastric glands.
The enterocytes in the small intestinal mucosa contain digestive enzymes that digest specific foods while they are being absorbed through the epithelium. These enzymes include peptidase, sucrase, maltase, lactase and intestinal lipase. This is in contrast to the gastric glands of the stomach where chief cells secrete pepsinogen.