Activity in the muscularis mucosae moves the villi which aids absorption by ensuring that the epithelial cells are frequently brought into contact with fresh material. There are multiple pacemakers in the small intestine. Different segments contract at different times so that the chyme is shunted back and forth. This action aids mixing and ensures that fresh material is continually brought into contact with the absorptive surfaces. Too rapid a transit through the gut can result in a serious loss of water and salts - with obvious cardiovascular effects.
Peristalsis is more frequent in the duodenum and jejunum than in the ileum.
Consequently chyme travels more slowly in the ileum than in the duodenum. The presence of fats in the chyme slows the movement of food along the intestine. The ileum projects a little way into the caecum so that, inthe presence of a pressure gradient, material can pass readily from the small to the large intestine but cannot easily pass in the opposite direction. The remainder of the large intestine is called the colon which leads to the rectum. In the large intestine there is a complete layer of circular muscle but there are only strips of longitudinal muscle, called taeniae coli.