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

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.