Stomach, pyloric valve and upper part of small intestine, called the duodenum

Your stomach is a muscular sac about the size of a small melon that expands when you eat or drink. It holds as much as a gallon (3.8 liters) of food or liquid. Once your stomach breaks down the food, strong muscular contractions known as peristaltic waves push the food toward the pyloric valve. This valve leads to the upper portion of your small intestine, a segment known as the duodenum.