What is Peristalsis?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon
A cow takes part in 'reverse peristalsis' when its digestive tract pulls cud back into the esophagus so that it can be chewed again.
A cow takes part in 'reverse peristalsis' when its digestive tract pulls cud back into the esophagus so that it can be chewed again.

Peristalsis is a series of muscle contractions and relaxations that occur along the course of the intestinal tract to push food and waste products through. In some cases, people can actually feel the contractions as they occur, especially in the case of movements of the large intestine. The basic principles behind this natural process in the body have also been adapted for peristaltic pumps, devices that utilize the same techniques used by the body to push fluids from place to place.

Vomiting is an example of the body overriding the usual muscle movements of peristalsis.
Vomiting is an example of the body overriding the usual muscle movements of peristalsis.

The way in which peristalsis works is fairly simple. When food or water enters the gastrointestinal tract, the muscles start to compress and relax in a wave-like motion to push the material through. In the case of someone swallowing a bite of apple, when the apple reaches the esophagus, bands of smooth muscle alternate squeezing and relaxing movements. As the muscle squeezes, the apple moves to the area where the muscle is relaxed, which will be further down the esophagus. The muscles further up stay contracted so that the food can't work its way back up, and eventually, the food reaches the stomach.

People can sometimes feel the movements of peristalsis in their large intestine.
People can sometimes feel the movements of peristalsis in their large intestine.

The stomach, in turn, forces its contents into the intestinal tract with peristaltic movements. The small intestines are constantly pushing material along so that it can be further broken down and digested, and to facilitate the expulsion of gas created as a byproduct of digestion so that the gas does not build up. By contrast, the large intestine goes through only two or three periods of big contractions every day, which are designed to push fecal material out of the anus.

Peristalsis begins with the esophagus.
Peristalsis begins with the esophagus.

This system is designed to prevent reverse peristalsis, in which food goes in the opposite of the desired direction. The body can sometimes have a wayward attitude, however, especially when it comes to getting rid of things which it deems harmful. Vomiting, for example, is caused by intense contractions of the abdominal muscles which push food back up through the esophagus, overriding the usual muscle movements.

The large intestine goes through two or three periods of big contractions every day, designed to push fecal material out of the anus.
The large intestine goes through two or three periods of big contractions every day, designed to push fecal material out of the anus.

People may sometimes refer jokingly to vomiting as “reverse peristalsis,” although this terminology is technically incorrect. Ruminants like goats and cows, however, do engage in this practice when they regurgitate cuds to chew on. In these animals, the digestive tract creates a vacuum that pulls partially-digested cuds into the esophagus, and then the animal uses muscle contractions to move the cud into the mouth so that it can be chewed again.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments

anon997779

w0wpow3r, ruminants such as cattle and goats eat grasses and other plants made largely of cellulose. Cellulose is extremely difficult to digest, so ruminants swallow the cellulose-heavy foodstuffs, let them sit in the rumen for a while to ferment (yes, ferment), then regurgitate it for further chewing. This is done several times a day, necessitating reverse peristalsis. Frequently and consistently forcing food up a pipe designed only for downward transit would undoubtedly cause damage to the esophagus.

Mind you, though, my field of expertise is accounting, so my understanding of this subject may be imperfect.

anon249565

@Belle1984: Based on the article, I think the difference is that vomiting is merely caused by intense contractions of the ab muscles, rather than systematic peristaltic movement of the esophagus.

The ab contractions "override" the esophogeal muscle that would ordinarily prevent food from coming out of the stomach.

belle1984

@w0wpow3r - One instance may be for cats, when they need to get rid of hairballs. They probably use reverse peristalsis to do so.

But I also don't quite get the difference between "reverse peristalsis" and "vomiting". It sounds like the same thing, just that vomiting is involuntary.

w0wpow3r

Why would an animal need to use reverse peristalsis? If the food is already chewed, isn't it already digestible?

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    • A cow takes part in 'reverse peristalsis' when its digestive tract pulls cud back into the esophagus so that it can be chewed again.
      A cow takes part in 'reverse peristalsis' when its digestive tract pulls cud back into the esophagus so that it can be chewed again.
    • Vomiting is an example of the body overriding the usual muscle movements of peristalsis.
      Vomiting is an example of the body overriding the usual muscle movements of peristalsis.
    • People can sometimes feel the movements of peristalsis in their large intestine.
      People can sometimes feel the movements of peristalsis in their large intestine.
    • Peristalsis begins with the esophagus.
      Peristalsis begins with the esophagus.
    • The large intestine goes through two or three periods of big contractions every day, designed to push fecal material out of the anus.
      The large intestine goes through two or three periods of big contractions every day, designed to push fecal material out of the anus.