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 expanding 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 involved in tight junctions by having enterocytes of various sizes. The microvillus length changes throughout the incubation and posthatch period with differences between the crypt and villus tip. The microvillus length on the villus tip increases after hatch, whereas the crypt microvillus length remains static. Across the intestinal segments, the microvillus length is longest on the villus tip and shortest on the crypt at day of hatch in all 3 species. The observations made in cellular structure, mitochondria and nucleus location, and lipid droplets are similar to reports by other researchers, but this is the first report of those observations in both duck and turkey. The tight junctions appear to be ensconced by day of hatch with little change in cell perimeter in the next 24 h. Potential for embryonic enterocytes exist with the appearance of a goblet cell originating along the basolateral membrane and extruding the enterocytes at day of hatch.