Fig. 1.

Radiation kills the crypt clonogenic cells. As successive clonogenic cells are killed, or reproductively sterilized, the cellular output onto the villi is reduced. Impaired cell production with continued upward cell migration leads to gradual villus and crypt shrinkage (blunting) resulting in reduced nutrient absorption and impaired barrier function. If no clonogenic cells remain in a crypt it will die and if sufficient crypts are killed ulcers will form. However, if one or more clonogenic cells remain the crypt will regenerate (B) and restore the blunted villi, ultimately regenerating the villus, with a slight ‘overshoot’ in cell production (C) before homeostasis and normal levels resume. A control crypt and villus is shown in (A). Adapted from Booth and Potten 2001.