Developmental changes in the ferret ileum during the postnatal period.

The development of the ferret ileum was studied in order to determine the pattern of morphological maturation during the postnatal period. In the newborn, intestinal villi were short, and lined by simple columnar enterocytes with striated borders and small vacuoles. At one week old, the equivalent cell had large vacuoles that were shown on TEM to be related to a tubulovesicular system in the apical region of the cytoplasm. At two and three weeks old, the epithelial cells at the same site showed a more extensive tubulovesicular system, and vacuoles occupied major areas of both the supra- and subnuclear cytoplasm. At six weeks old (weaning), although the enterocytes contained a few small intracellular vesicles, they appeared histologically more mature than in previous stages. At nine weeks and in the adult, the villi were longer and the enterocytes no longer contained vacuoles. In TEM, the epithelial cells had long microvilli, and the apical tubulovesicular system and vacuoles had completely disappeared from the cytoplasm.