The colon is divided into four parts, the ascending, transverse, descending and sigmoid colon. On average the colon is 1,5 meters long and its main function is to reassert fluid, electrolytes, and vitamins.
Since the large intestine has no villi or plica circularis the mucosa is smooth. Simple tubular intestinal glands (crypts of Lieberkuhn) extend through the entire thickness of the mucosa. The surface columnar epithelium and the cells lining the crypts are enterocytes, with an oval basal nucleus and apical brush border, the microscopic representation of microvilli. There are also numerous mucous secreting goblet cells recognized by their content of a large mucous globule. The lamina propria with connective tissue and inflammatory cells surround the crypts. A thin smooth muscular layer, the lamina muscularis mucosa marks the border between the mucosa and submucosa.
The submucosa consists of loose connective tissue with blood vessels and nerves. Some solitary lymph follicles are also seen.
The muscular layer (muscularis externa) consists of an inner circular smooth muscle layer, the outer longitudinal muscle layer is not continuous as in the rest of the gastrointestinal tract. It is divided into three thickened muscular bands, called taenia coli.