GI Phasic Contraction: Segmentation
Segmentation is local movement that is dominant in the small and large intestines. During segmentation, a ring of circular muscle contracts, while the muscle on either side relaxes. Contraction and relaxation waves oscillate along a length of intestine, with contracted areas giving way to relaxation and vice versa, so the activity mixes the luminal contents. Because segmentation elevates luminal pressure in the area in which it occurs, it may help move chyme along the tract. The intensity of these movements varies in different parts of the GI tract. Segmentation is discussed in more detail in a later section.