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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]
The gastric chief cell (also known as a zymogenic cell or peptic cell) is a cell in the stomach that releases pepsinogen [1] and chymosin.Pepsinogen is activated into the digestive enzyme pepsin when it comes in contact with hydrochloric acid produced by gastric parietal cells. [2]
A gastric chief cell, peptic cell, or gastric zymogenic cell is a type of gastric gland cell that releases pepsinogen and gastric lipase. It is the cell responsible for secretion of chymosin (rennin) in ruminant animals and some other animals. [ 1 ]
It is produced in the stomach by gastric chief cells in its inactive form pepsinogen, which is a zymogen. Pepsinogen is then activated by the stomach acid into its active form, pepsin. Pepsin breaks down the protein in the food into smaller particles, such as peptide fragments and amino acids.
Chyme slowly passes through the pyloric sphincter and into the duodenum of the small intestine, where the extraction of nutrients begins. Gastric juice in the stomach also contains pepsinogen. Hydrochloric acid activates this inactive form of enzyme into the active form, pepsin. Pepsin breaks down proteins into polypeptides.
Water is a very minor source of hydrogen ions in comparison to carbonic acid. Carbonic acid is formed from carbon dioxide and water by carbonic anhydrase. The bicarbonate ion (HCO 3 −) is exchanged for a chloride ion (Cl −) on the basal side of the cell and the bicarbonate diffuses into the venous blood, leading to an alkaline tide phenomenon.
The enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water to form carbonic acid. This acid immediately dissociates into hydrogen and bicarbonate ions. The hydrogen ions leave the cell through H + /K + ATPase antiporter pumps. At the same time, sodium ions are actively reabsorbed [citation needed].
Gastric chief cell Parietal cell. Chief cells (zymogen cells/peptic cells) – They are found in the basal regions of the gland and release proenzymes or zymogens – pepsinogen (precursor to pepsin), and prorennin (precursor to rennin or chymosin). [10] Prorennin is secreted in young mammals (childhood stage). It is not secreted in adult mammals.