GUT ENDOCRINE CELLS IN INSECTS: THE ULTRASTRUCTURE OF THE ENDOCRINE CELLS IN THE COCKROACH MIDGUT

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Abstract
Endocrine cells in the epithelia of the midgut and enteric caeca of the adult cockroach were examined under an EM. Gut endocrine cells develop in the regenerative cell-mass, the nidus, and are singly intercalated among the columnar cells. They are bowl-shaped, pyramidal or bottle-shaped, standing on the basement lamina and extending toward the luminal side. The fine structures of the basal-granulated cells are principally the same as those reported in the alimentary mucosa of mammals, except that the cells in the insect are mostly closed in type. At least 6 types of endocrine granules were identified: I, round type granules (a) dense and medium-sized (200-300 nm), (b) dense and large-sized (300-400 nm), (c) pale and various-sized (200-400 nm); and II, irregular type granules (a) dense and medium-size (200-300 nm), (b) dense and very large-sized (700-800 nm) and (c) pale and very large-sized (700-800 nm). The endocrine cells were temporarily classified by reference to the granules and at least 4 cell types were identified: the type I-a cell is reminiscent of the human M-cell, the type I-b cell, of the human L-cell, the type I-c cell, of human D-like cell; the type II cells are reminiscent of the EC cells of the human alimentary mucosa. Exocytotic granule release in the basal-granulated cells and nerve-muscle junctions in the longitudinal musculature of the gut also are described.