Intestinal Motility and Laxative Action

Abstract

The coordinated contractions of the smooth muscle of the intestine cause chyme to mix with intestinal fluids and to move aborally. Waves of contractions in the small intestine cause rhythmic segmentation, which rapidly mix the luminal contents. These nonpropulsive movements are accompanied by peristaltic movements, waves of contraction and relaxation that push the intestinal contents toward the colon (Weisbrodt 1987). Colonic motility also has seg-menting-type movement; contraction and relaxation of the interhaustral rings, which churn the semi-liquid fecal material. By slowing down this process (colonic motility), absorption of water and electrolytes takes place until semi-solid feces (100–250 g per day) are formed in the most distal part of the colon. Retrograde contractions cause aberrant or slow transit, while the postprandial motor activity encourages movement of the intestinal contents towards the rectum.