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peristalsis:see digestive systemdigestive system,
in the animal kingdom, a group of organs functioning in digestion and assimilation of food and elimination of wastes. Virtually all animals have a digestive system. In the vertebrates (phylum Chordata, subphylum Vertebrata) the digestive system is very complex.
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a wavelike contraction that propels the contents of tubular organs, for example, the intestine, stomach, and ureters, caudally in animals or in a downward direction in man. Peristalsis is the result of many coordinated contractions of the longitudinal and transverse muscles in the walls of a tubular organ. A single peristaltic wave takes the form of a circular constriction around the lumen that moves along the length of the organ. The walls of the organ are always slightly relaxed before the arrival of the constriction, so that the wave appears to push the contents in the direction in which it travels. Peristaltic waves follow each other continuously at a fixed rhythm and rate. In man, for example, the peristaltic rhythm of the stomach is 3 waves/min, with each wave moving at the rate of 0.5 cm/sec; intestinal peristalsis occurs at the rate of 6 waves/min.
Peristalsis is conditioned by the ability of smooth muscles to contract automatically and by the functioning of nerve plexuses in the muscles. The autonomic nervous system and humoral factors regulate peristalsis. Furthermore, the central nervous system, including the cerebral cortex, may participate in the regulation of peristalsis. This was experimentally demonstrated in animals by inducing changes in peristaltic patterns using conditioned reflexes. Observations on humans show that anger and pain inhibit peristalsis, whereas fear sometimes intensifies it; these observations are taken as further evidence that the cortex may have a role in peristaltic control. However, peristalsis is well indicated in isolated parts of the intestine. Medications and the physical and chemical properties of foods also affect peristalsis.