Peristalsis is the contraction of muscles in the gastrointestinal tract that allows food and digestive contents to flow from one digestive organ to the next. peristalsis begins in the esophagus, where it helps move swallowed food toward the stomach. Peristalsis continues in the stomach, small intestine, large intestine, and rectum assisting in the passage of partially digested food, fluids, and waste items through the digestive tract.