What is the role of Stomach in human body?

The stomach serves both to digest food and to hold it so that it can be gradually released into the small intestine. Food stays in the stomach two to three hours. The muscular walls of the stomach churn food until it is a semiliquid mixture called chyme.

Glands in the walls of the stomach release pepsinogen and hydrochloric acid through tiny openings called gastric pits. The pepsinogen is converted to pepsin at low pH conditions, which is maintained by the presence of hydrochloric acid in the stomach. Pepsin serves as the initial step in the breakdown of protein, and hydrochloric acid kills bacteria that enter the stomach along with the food. A protective mucus lining is secreted by the stomach to stop the action of pepsin, so the stomach does not digest itself, since hydrochloric acid could also eat away and damage the stomach wall. Bacterial infections and other conditions can interfere with mucus production, leading to ulceration of the stomach lining.

Chyme is released from the stomach in spurts into the duodenum, the closest or proximal part of the small intestine, through an opening controlled by relaxation of a circular muscle called the pyloric sphincter. At the opening from the esophagus to the stomach, the cardiac sphincter prevents reflux of chyme into the esophagus, where it could cause the discomfort known as heartburn.