Gastric juice is a strong acidic liquid which is produced by the gastric glands in the lining of the stomach. It has a pH 1 to 3 in humans, which is close to being colourless. The hormone gastrin is released into the bloodstream and causes gastric glands to secrete gastric juice. The gastric juice main components are digestive enzymes pepsin and rennin (rennin found in babies), hydrochloric acid, and mucus.
Gastric juice 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 B 12 ; absence of this substance results in pernicious anemia, or B 12 deficiency.