Origin and renewal of the four types of epithelial cells in the mouse small intestine.

The electron microscope, with or without radioautography, was used to examine the life history of the four cell types of the epithelium of the small intestine: columnar, mucous, argentaffin and Paneth cells. All four are derived from epithelial cells which are rich in free ribosomes and therefore, considered to be immature; they are situated next to Paneth cells at the base of the crypts. Young stages of each cell type are similar to the immature epithelial cells. This resemblance is gradually lost with age as the cells migrated away from the crypt base. Columnar and mucous cells behave in a similar way. Young cells are proliferative; as they mature they migrate up the villi and are lost into the lumen of the intestine. Most young argentaffin cells are not proliferative. Mature cells are also lost from the population via the villous tips. Paneth cells do not proliferate nor migrate but degenerate in situ and are phagocytosed by adjacent immature epithelial cells