Peristalsis in Intestine for Digestion
Gastrointestinal Peristaltic Waves, Intestinal Motility & Absorption
Peristalsis is a series of wavelike contractions occurring in the smooth muscle layer of the gastrointestinal tract. It is a physiological process that results in intestinal motility and propulsion of ingested food along the intestines for absorption of nutrients.
Peristalsis and Digestion
Peristalsis, a reflex propulsive movement, occurs along the length of the gastrointestinal tract, from the esophagus to the rectum. It starts as a ring-like constriction initially which later moves forward along the intestines. It can be compared to compressing a distended tube by putting one’s fingers around it and then moving the fingers along the tube, in the process moving the contents of the tube in the same direction.
It occurs in any tube like structure in the human body which contains smooth muscle fibers. So this process occurs in the gastrointestinal tract, bile duct, ducts of various glands and the ureters.
In the gastrointestinal tract, it helps propel food to be digested along the intestines. In the process, it also helps spread the food particles along the intestinal wall for effective digestion and absorption.
Peristalsis – Stimulus and Mechanism
The stimulus for peristalsis is distension or expansion of the gut. When it fills up with food to be digested, the gut wall stretches. This stretching acts a reflex mechanism that stimulates the circularly arranged smooth muscle in the wall of the gut, about 2 or 3 cm before the point of distension. The smooth muscle contracts as a result, its circular arrangement causing the contraction to form a ring-like constriction of the intestine. This contraction then moves along the length of the gut.
Any physical or chemical irritation to the lining of the intestine can also initiate peristalsis.
Peristalsis and the Myenteric Plexus
These stretch reflexes are brought about by a network of nerve fibers, called the myenteric plexus, located within the layers of the gut wall. Active participation of this plexus is required for effective peristalsis.
Peristalsis – Direction of Movement
The myenteric plexus is also important in governing the direction of movement of peristalsis. Once peristalsis starts, the movement can occur in both directions, but the effective direction is oral to anal.
When the peristaltic contraction appears, the part of the gut away from it (towards the rectum, that is) actually relaxes, so that it receives the food being pushed. This, along with the fact that the contraction starts 2 to 3 cm before the distension, ensures that the peristaltic wave travels towards the rectum.
The rate of contraction varies from 2 to 25 cm per second.
Peristalsis and Vomiting
When the upper part of the gastrointestinal tract becomes excessively distended or irritated, an anti-peristaltic wave may be initiated, causing the contractions to travel backwards towards the oral cavity, resulting in vomiting.
Peristalsis in the small intestine is usually weak. However, intense irritation of its lining in infectious conditions can lead to powerful and rapid peristalsis, resulting in diarrhea. Some drugs may also cause diarrhea by chemical stimulation of the gut mucosa.
Peristalsis, a series of wavelike movements of the intestines, is a physiologic process responsible for intestinal motility, propulsion of food and its absorption.
Sources:
Ganong, William F. “Review of Medical Physiology” (McGraw Hill; 22nd edition, 2005)
Watch a movie showing peristalsis in the esophagus.
Peristalsis in Intestine for Digestion
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Peristalsis in Intestine for Propulsion of Food
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