Three or four times each day, the circular muscles in large parts of the transverse and descending colon undergo several strong peristaltic contractions, called mass movements. Each mass movement contraction extends over 20 cm of the colon and propels the colon contents a considerable distance toward the anus. Mass movements are stimulated by irritation or distention of the colon, local reflexes in the enteric plexus, and intense parasympathetic stimulation. The gastrocolic and duodenocolic reflexes are local reflexes that can stimulate mass movements( figure 21.25, steps 1 and 2 ) The gastrocolic reflex is initiated in the stomach and the duodenocolic reflex is initiated in the duodenum. The ehought or smell of food, distention of the stomach, and the movement of chyme into the duodenum can stimulate these reflexes. Mass movements are most common about 15 minutes after breakfast. They usually persist for 10-30 minutes and then stop for perhaps half a day.