Asynchronous development of the rat colon.

Mucosal ridge and fold formation, apoptosis and the occurrence of secondary lumina within the epithelium are morphological features associated with the development of the colon. These processes, however, do not occur synchronously in the various segments of the colon. In the caecum and ascending colon of the rat, fold formation, apoptosis and secondary lumina result in the development of villi by day 22 after conception, and by postnatal day 3 in the transverse colon. These villi persist in the rat colon until approximately postnatal day 10. The presence of colonic villi may be correlated with the increased food intake and fluid absorption during this early postnatal period. Villus formation does not take place in the developing descending colon.