Expression of Digestive and Absorptive Function in Differentiating Enterocytes

The intestinal epithelium is a labile tissue capable of changing its properties rapidly in response to alterations in its immediate environment. These changes have been classified recently according to whether they take place in a con­ tinuous or discontinuous manner. Discontinuous events occur at birth and at weaning; continuous events occur throughout the life of the animal (34). I would like to begin this review by suggesting that this type of division is to some extent artificial. The main problem that is always faced by an intestine is how to make nonfunctional cells differentiate within a strictly limited and often variable period of time. The mesenchyme plays an essential role in enabling the enterocyte to achieve this end. This basic drive to differentiate is further influenced by hormones, and much has already been written about this aspect of development. This review concentrates instead upon more recent work that shows the prime importance of mesenchyme in laying down basic rules for enterocyte development. Comparisons are also made between different aspects of normal enterocyte development measured at the cellular level.