gastric juice(redirected from Digestive juices)
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gastric juice,thin, strongly acidic (pH varying from 1 to 3), almost colorless liquid secreted by the glands in the lining of the stomach. Its essential constituents are the digestive enzymes pepsinpepsin,
enzyme produced in the mucosal lining of the stomach that acts to degrade protein. Pepsin is one of three principal protein-degrading, or proteolytic, enzymes in the digestive system, the other two being chymotrypsin and trypsin.
..... Click the link for more information. and rennin (see rennetrennet,
substance containing rennin, an enzyme having the property of clotting, or curdling, milk. It is used in the making of cheese and junket. Rennet is obtained from the stomachs of young mammals living on milk, especially from the inner lining of the fourth, or true,
..... Click the link for more information. ), hydrochloric acid, and mucus. Pepsin converts proteins into simpler, more easily absorbed substances; it is aided in this by hydrochloric acid, which provides the acid environment in which pepsin is most effective. Rennin aids the digestion of milk proteins. Mucus secreted by the gastric glands helps protect the stomach lining from the action of gastric juice. Gastric secretion is stimulated by a number of hormones and chemical substances, by the presence of food in the stomach, and by a number of psychological factors, such as the smell of a favorite food. A decrease or total absence of gastric juice secretion may be a congenital abnormality or a concomitant of advanced age. Certain cells of the stomach lining secrete a substance known as intrinsic factor, which is necessary for the absorption of vitamin B12; absence of this substance results in pernicious anemia, or B12 deficiency (see vitaminvitamin,
group of organic substances that are required in the diet of humans and animals for normal growth, maintenance of life, and normal reproduction. Vitamins act as catalysts; very often either the vitamins themselves are coenzymes, or they form integral parts of coenzymes.
..... Click the link for more information. ).
a complex digestive juice secreted by various cells of the gastric mucosa; it is a colorless, slightly opalescent fluid. It contains the following enzymes: pro-teases (pepsins, rennin, gastricsin, and gelatinase), which accomplish the initial stages of protein decomposition; and a small quantity of lipase, which mainly decomposes emulsified fats. It also contains hydrochloric acid (concentration in humans is 0.4-0.5 percent) and mucus.
Hydrochloric acid activates enzymes and facilitates the decomposition of proteins, causing their denaturation and saturation; it conditions the bactericidal properties of gastric juice (inhibits the development of putrefactive processes in the stomach), and stimulates the secretion of gastric hormones. Hydrochloric acid in gastric juice is partly in a free state and partly bound (with proteins). The total acidity of gastric juice in man after a test breakfast is 40-60 conventional units; free acidity is 20-40 units. In some dysfunctions of the stomach, the hydrochloric-acid content of the gastric juice may increase or decrease to the point of complete absence (so-called achylia). Mucus, whose composition includes mucoproteins, protects the walls of the stomach from mechanical and chemical irritants. Gastric juice contains Castle’s intrinsic factor, which facilitates absorption of vitamin B12.
The secretion of gastric juice is determined in the first, compound-reflex phase of secretion by the appearance, odor, and taste of food; in the second, neurohumoral, phase, it is determined by chemical and mechanical stimuli to the gastric mucosa. Up to two liters of gastric juice is secreted by a human being every 24 hours. The quantity, composition, and properties of gastric juice vary according to the type of food in the stomach, and also when there are diseases of the stomach, intestine, or liver. Gastric juice is tested in humans by means of probing the stomach after the application of various natural and pharmacological stimuli; in animals it is tested by means of an artificially formed isolated stomach, according to a method perfected by I. P. Pavlov. Gastric juice obtained from animals is used internally in treating some diseases of the digestive organs.
V. G. KASSIL’ and IA. O. OL’SHANSKII