The name for the waves of contractions that propel substances along a tract is peristalsis. Peristalsis is a coordinated muscular contraction and relaxation that propels food, digestive juices, and other substances through the digestive tract. It is an important part of the digestive process and helps to move food from the mouth to the stomach, and then through the small and large intestines. The jejunum is a part of the small intestine, the fundus is the upper portion of the stomach, and the pyloric sphincter is a muscular valve that controls the flow of food from the stomach to the small intestine.