They are replaced by epithelial cells along the lateral walls of the villi, which differentiate from stem cells. At the beginning of differentiation, the cell undergoes several more divisions, so that the number of differentiating descendants of one stem cell increases many times. At the tip of the villi, the cells last no more than one day, then they die and are rejected.
Few cells as a result of division fall to the very bottom of the crypt. Intestinal epithelium forms villi protruding into the intestinal cavity. After division, apparently by accident, one of the cells is closer to the edge of the crypt - it enters the path of further, terminal differentiation. Between the villi in the wall of the intestine are recesses - crypts, near the bottom of which stem cells are located and divide. They differentiate into specific Pennet cells. Differentiated cells of several types line the surface of the villi, come into contact with food, promote its digestion and absorb soluble food substances. The same cell, which after dividing the initial stem cell accidentally appears near the bottom of the crypt, retains its slightly differentiated character, that is, it remains the stem.