Peristalsis is the name for the waves of contractions that propel substance s along a tract. It is a series of wave-like contractions that moves food to different processing stations in the gastrointestinal tract and starts in the esophagus when the boluses of food are swallowed. The wave motion is produced by the longitudinal smooth muscles that line up the esophagus, stomach, small intestines and the colon and is triggered by presence of food.