Internal lining of the small intestine is a good example of epithelium that specializes in absorbing nutrients and allowing them to pass from the intestinal cavity to the blood.
The high absorption capacity of the intestinal epithelium is due to the fact that its cells have, in the membrane, the free edge (ie, the edge facing the intestinal cavity), many thin, elongated projections that resemble glove fingers called microvilli. .
Calculations of the membrane area constituting microvilli show that they increase the surface area of each cell five hundred times compared to the area of cells that have the smooth edge. The same kind of calculation leads us to conclude that the human small intestine has an absorption surface of over 300 m2, equivalent to the area of a 20 m long and 15 m side sports court.
THE mitosis It is a frequent process in epithelial cells, which are short-lived and need to be constantly renewed. The speed of this renewal varies from epithelium to epithelium. The most rapidly renewing cells are from the intestinal epithelium: within 2 to 5 days they are replaced by new cells. The slowest renewing ones are the pancreas cells that take 50 days to replace.
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In the skin, epidermal renewal occurs on average every 30 days. In the scalp, a dysfunction may occur where peeling of the epidermis occurs every 3 or 4 days, forming the dandruff.