An enterocyte is a type of cell that absorbs water and nutrients from the digestive tract. As an example of what is called a columnar cell, it is tall and narrow in shape, with a "brush" border made of tiny protrusions which project into the space inside the gut. Enterocytes originate inside intestinal glands, or crypts, in the small intestine and colon. In the small intestine, they produce and secrete digestive enzymes, which bind to their brush borders and help break down sugars and proteins, making them smaller and easier to absorb. Enterocytes in the large intestine absorb water and electrolytes.
The wall of the small intestine is arranged into finger-like projections called villi. After being formed inside crypts at the bottom of the villi, enterocytes migrate all the way to the tips, maturing as they go. At the tips of the villi, cell death occurs and the enterocytes are sloughed off into the gut. The life cycle of an enterocyte lasts for only a few days, and in the small intestine the resulting rate of renewal of the lining is more rapid than for any other body tissue. In the colon, there are no villi, but there are crypts where enterocyte formation takes place.
Enterocytes are simple columnar epithelial cells, which are shaped like elongated boxes. As intestinal absorptive cells, they are found in both the large and small intestine. Each enterocyte has an oval nucleus situated in the lower part of the cell. At the top of the cell, the brush border, which is made of tiny protrusions called microvilli, greatly increases the surface area available for absorption of nutrients or water from the gut.
Digestive enzymes known as peptidases and disaccharidases are produced by each enterocyte. These attach themselves to the microvilli on the top of the cell, breaking down proteins and sugars from the gut into smaller particles that are more easily absorbed. In the colon, enterocytes absorb water and electrolytes, and although they also have microvilli on their upper surfaces, these do not contain digestive enzymes.
Substances pass from the gut into enterocytes and from there they move out into the fluid that surrounds the cells, known as interstitial fluid. An enterocyte has a number of active transport systems it uses to pump substances across its cell membrane and into the cell. Once they reach the interstitial fluid, nutrients are able to pass into tiny blood vessels called capillaries, which connect to the general blood circulatory system.