BIOL 221 Study Guide - Final Guide: Internal Anal Sphincter, External Anal Sphincter, Stratified Squamous Epithelium
11 Feb 2020
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Numerous goblet cells located in the mucosa secrete mucus that helps make passage of the chyme easier. The mucosa has simple columnar epithelium until the distal end of the anal canal where it changes to stratified squamous epithelium. The submucosa is thinner with less lymphatic tissue than in the small intestine. The longitudinal layer of the muscularis is modified as the teniae coli; the circular layer is normal. This causes the large intestine to form pouch-like structures called hastra (singular = haustrum). The serosa covers most of the large intestine except that parts of the ascending and descending colon and the structures that are in the pelvic cavity. Epiploic appendages are little fat-filled pouches of unknown function that are attached to the serosa. Haustral churning (also called haustral contraction) moves chyme slowly from one haustrum into the next; it occurs based on stretching of the smooth muscle that contracts when it has been sufficiently stretched.
