This slide shows a cross section of the duodenum (a portion of the small intestine). Note that there are two relatively thick layers of smooth muscle cells that run perpendicular to one another, an outer (thinner) longitudinal layer and an inner (much thicker) circular layer of smooth muscle.  Peristaltic contractions of these two opposing layers of  muscle keep food moving through the gut.

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The address of A/P Lab is:  http://bioweb.uwlax.edu/aplab/      Direct comments or questions to gillis.rick@uwlax.edu