Physiology, Peristalsis

Excerpt

Two types of movements occur in the gastrointestinal (GI) tract; peristalsis and segmentation. Peristalsis is the involuntary contraction and relaxation of longitudinal and circular muscles throughout the digestive tract, allowing for the propulsion of contents beginning in the pharynx and ending in the anus. Swallow-induced peristalsis is termed primary peristalsis, while peristalsis evoked by distension of the esophagus is termed secondary peristalsis. While peristalsis propels contents forward, segmentation is the mixing of these contents, both of which play an essential role in allowing for the absorption of water and nutrients.

The GI tract is innervated by the enteric nervous system (ENS), a division of the peripheral nervous system, which controls the GI system independent of any central nervous system (CNS) input. The ENS consists of two networks of nerves, the myenteric plexus (Auerbach plexus) and the submucosal plexus (Meissner plexus). The myenteric plexus is situated between the longitudinal and circular muscles of the GI tract and contains the pacemaker cells of the GI tract and the interstitial cells of Cajal (ICC). The myenteric plexus and ICC mediate the process of peristalsis by alternating between distal relaxation and proximal contraction of the muscles.