The main function of the stomach is to chemically and mechanically break down food. It accomplishes this by secreting stomach acid and enzymes to digest food and churning the food by the periodic contraction of the stomach muscles.
When food enters the mouth it is swallowed and enters the esophagus. Food travels down the esophagus and enters the stomach through a muscular valve known as the lower esophageal sphincter. It is broken down by stomach acid and churned into a substance known as chyme. Then, the food travels through the pyloric sphincter and passes into the small intestine where it can be further digested.