Intestinal epithelium

Intestinal epithelium
Simple columnar epithelial cells
Anatomical terminology []

The intestinal epithelium is the layer of cells that forms the luminal surface or lining of both the small and large intestine (colon) of the gastrointestinal tract. It is composed of simple columnar epithelium. It has two important functions: absorbing helpful substances and providing a barrier against harmful substances. Some diseases and conditions are caused by dysfunction in the intestinal epithelium, and some diseases and conditions cause problems with these cells, which then leads to further complications.

The epithelium is part of the intestinal mucosa layer. The epithelium is composed of a single layer of cells. The other two layers of the mucosa, the lamina propria and the muscularis mucosae, support and articulate the epithelium layer. To securely contain of 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 renewal and migration. Renewal relies on proliferative cells (stem cells) that reside at the crypt base of the intestinal glands (epithelial invasions into the underlying connective tissue). After being formed at the base, the new cells migrate upwards and out of the crypt. Eventually, they undergo apoptosis and are shed off into the intestinal lumen. In this way, the total number of cells making up the intestinal epithelium 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 cylindrical tube, is achieved by three anatomical factors: