Fine structure of the small intestinal epithelium of bolti fish in Egypt [tilapia nilotiza]

ABSTRACT

The ultrastructure of the epithelial lining of the small intestine of Tilapia nilotica was studied using transmission electron microscopy. The surface epithelium comprised 4 cell types absorptive, goblet, clear and enteroendocrine cells. The absorptive enterocytes represented the predominant cell type. They were cylindrical in shape and their luminal plasmalemmae were thrown into symmetrical parallel microvilli from which microfilamentous bundles extended to the underlying terminal web zone. The latter, showed organelle-paucity and it contained pinocytotic vesicles emanating from the intermicrovillar spaces. The supranuclear cytoplasm, subjacent to the terminal web, was rich in mitochondria, ribosomes, profiles of endoplasmic reticulum and vesicular elements. The nucleus occupied the middle or the lower third of the cell and it exhibited a highly euchromatic character. The infranuclear cytoplasm was particularly rich in mitochondria and some electron-dense microbodies. The goblet cells were insinuated amongst the absorptive ones but their luminal surfaces were devoid of microvilli. Abundance of membrane-bounded granules of different electron-density and peripheral profiles of rough endoplasmic reticula were characterising such cells. The clear cells were always situated near the basal membrane but not reaching the luminal surface. The intravesicular fat droplets were a consistent feature in such organelle-deficient cells, the endocrine cells were cylindrical in shape, with their bases resting on the basal lamina and apeces reaching the lumen. Their cytoplasm was packed with spherical granules of different electron-density