in Digestion and Absorption (Digestive System and Nutrition) by

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Smooth muscles of the GI tract produce two kinds of motility, called (1) peristalsis and (2) segmentation.

The functions of peristalsis and segmentation are different.

Peristalsis - Propels the contents of the lumen onward, one way motion, moves food through a sphincter into the stomach, symmetrical contraction and relaxation of muscles, occurs in all parts of the GI

Segmentation - Contractions move chyme in both directions, greater mixing, smooth muscle contract and relax in seemingly random fashion.

Segmentation mixes the contents of the lumen (back-and-forth mixing of the contents of the lumen). Segmentations are localized mixing contractions in the small intestine that swirl the chyme in one section of the intestine but do not move it along the tract.