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Concept
Intestinal epithelium
Summary
The intestinal epithelium is the single cell layer that form the luminal surface (lining) of both the small and large intestine (colon) of the gastrointestinal tract. Composed of simple columnar epithelial cells, it serves two main functions: absorbing useful substances into the body and restricting the entry of harmful substances. As part of its protective role, the intestinal epithelium forms an important component of the intestinal mucosal barrier. Certain diseases and conditions are caused by functional defects in the intestinal epithelium. On the other hand, various diseases and conditions can lead to its dysfunction which, in turn, can lead to further complications.
The intestinal epithelium is part of the intestinal mucosa. The epithelium is composed of a single layer of cells, while the other two layers of the mucosa, the lamina propria and the muscularis mucosae, support and articulate the epithelial layer. To securely contain the contents of the intestinal lumen, the cells of the epithelial layer are joined together by tight junctions, thus forming a contiguous and relatively impermeable membrane.
Epithelial cells are continuously renewed every 4–5 days through a process of cell division, maturation, and migration. Renewal relies on proliferative cells (stem cells) that reside at the crypt (base) of the intestinal glands (epithelial invaginations into the underlying connective tissue). After being formed at the base, the new cells migrate upwards and out of the crypt, maturing along the way. Eventually, they undergo apoptosis and are shed off into the intestinal lumen. In this way, the lining of the intestine is constantly renewed while the number of cells making up the epithelial layer remains constant.
In the small intestine, the mucosal layer is specially adapted to provide a large surface area in order to maximize the absorption of nutrients. The expansion of the absorptive surface, 600 times beyond that of a simple cylindrical tube, is achieved by three anatomical features:
Circular folds are transverse folds that slow the passage of the luminal contents and serve to expand the total surface area threefold.
Official source
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