After being swallowed, the food enters the stomach through the Lower Esophageal Sphincter, or LES. The upper stomach, or fundus relaxes as the stomach fills with food. This allows a person to eat more food. As the stomach fills with food, it releases acid. The acid helps break down the food and kill bacteria. Then, the stomach starts to contract and relax. This grinds up the food into smaller pieces.

When the food is ground up into small enough pieces, it empties or leaves the stomach through a muscular ring called the pyloric sphincter. The pyloric sphincter opens up to let food pass from the stomach to the small intestine where nutrients are digested and absorbed.