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The large intestine consists of the cecum, the colon, and the rectum, which share the same wall structure formed by, from inside to outside, a mucosa, a submucosa, a muscularis interna, a muscularis externa, and a serosa. The mucosa of the large intestine, comprising simple columnar epithelium and a lamina propria, forms deep cavities, the crypts of Lieberkühn, and, unlike the small intestine, lacks villi. The epithelium contains absorptive enterocytes with apical microvilli and many oval, mucous goblet cells. Deep in the crypts the epithelium contains enteroendocrine cells with granules in the cell portion facing the lamina propria. Large lymphoid aggregates, Peyer’s patches, occur in the submucosa throughout the intestines; M cells form part of the epithelium covering the Peyer’s patches.
The colon of the mouse has long crypts of Lieberkühn and a poorly developed muscularis mucosae. The colon consists of an ascending, a traverse, and a descending portions. The ascending colon contains more mucus than the descending colon and its mucosa forms transverse folds. The mucosa and submucosa of the descending colon form longitudinal folds. The descending colon is enveloped in serosa almost to the anus, which makes the mouse susceptible to “rectal” prolapses.
The 4X micrograph is a cross section of the colon, demonstrating its folded mucosa. The 10X and 20X micrographs display the mucosa in increasing detail. The goblet cells and the simple columnar epithelium are shown close-up in the 40X micrograph.
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