Stomach

The stomach is a J-shaped organ that lies between the esophagus and the small intestine in the upper abdomen. The stomach has 3 main functions: to store the swallowed food and liquid; to mix up the food, liquid, and digestive juices produced by the stomach; and to slowly empty its contents into the small intestine.

Only a few substances, such as water and alcohol, can be absorbed directly from the stomach. Any other food substances must undergo the digestive processes of the stomach. The stomach's strong muscular walls mix and churn the food with acids and enzymes (gastric juice), breaking it into smaller pieces. About 3 quarts of the gastric juice is produced by glands in the stomach every day.

The food is processed into a semiliquid form called chyme. About 4 hours or so after eating a meal, the chyme is slowly released a little at a time through the pyloric sphincter, a thickened muscular ring between the stomach and the first part of the small intestine called the duodenum.