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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