Food then passes down the esophagus to the stomach. Because both food and air pass through the pharynx , it is important to prevent food from getting into the lungs. During swallowing the larynx is pulled upward . This causes a flap of tissue called the epiglottis to cover the opening to the trachea and prevent food from entering the trachea. In the stomach , additional liquid, called gastric juice is added to the food.
Gastric juice contains enzymes and hydrochloric acid.
The major enzyme of the stomach is pepsin, which initiates the chemical breakdown of protein. The pH of gastric juice is very low, generally around pH 2. The combined activities of enzymatic breakdown, chemical breakdown by hydrochloric acid, and mechanical processing by muscular movement result in a thoroughly mixed liquid called chyme . Chyme eventually leaves the stomach through a valve known as the pyloric sphincter and enters the small intestine . The first part of the small intestine is known as the duodenum.