MOLECULAR, CELLULAR, AND DEVELOPMENTAL BIOLOGY Survey of Enterocyte Morphology and Tight Junction Formation in the Small Intestine of Avian Embryos

ABSTRACT The developing villus in the small intestine is covered by a single cell layer epithelium where tight junctions are present between the individual enterocytes. As the incubation period proceeds, the epithelium is ex-panding both in area as well as replenishing epithelial cells. The formation of tight junctions was evaluated in the small intestinal segments of the chicken, duck, and turkey in the final days of incubation and the first few days posthatch. The percentage of enterocyte membrane involved in tight junctions decreased as day of hatch approached followed by an increase in the 3 d after hatch. The rapid increase of epithelial cell proliferation at day of hatch may affect the percentage of cell membrane in-volved in tight junctions by having enterocytes of various sizes. The microvillus length changes throughout the in