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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.
In the mouse, the rectum is particularly short. The mucosa and submucosa of the rectum form longitudinal folds. The rectum has a well-developed muscularis mucosae, a thick muscularis interna, and a thin muscularis interna.
In the 4X micrograph of the rectum a Peyer’s patch is visible. The 10X and 20X micrographs present, in increasing detail, the mucosa and the well-developed muscularis mucosae. The 40X micrograph offers details of the crypts of Lieberkühn containing many Goblet cells and, in the inset, the thick muscularis interna and thin muscularis externa.
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