peristalsis

(per-i-stal′sĭs )

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[ peri- + Gr. stalsis, contraction]
A progressive wavelike movement that occurs involuntarily in tubular structures of the body, esp. the alimentary canal. It is characteristic of tubes possessing longitudinal and circular layers of smooth muscle fibers.
Peristalsis is controlled reflexively by distention of the walls of the tube. The wave consists of contraction of the circular muscle proximal to the distention with relaxation of the region immediately distal to the distended portion. The simultaneous contraction and relaxation progress slowly for a short distance as a wave that causes the contents of the tube to be forced onward.

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