The stomach has longitudinal, vertical and diagonal muscles that contract the stomach in churning movements that mix the food. Stomach contents are mixed about every 20 minutes. Churning, mixing and addition of stomach acid convert food to a nutrient broth called acid chyme . The passage of acid chyme into the small intestine is regulated by the pyloric sphincter at the bottom of the stomach. The pyloric sphincter relaxes at intervals and permits small quantities of chyme to pass.
Gastric secretion is controlled by nerve impulses and the hormone gastrin .
The stomach epithelium contains three types of secretory cells.