Electron Microscopic Study on Capillary Endothelial Cells of the Adrenal Cortex

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Abstract
An experimental study was made on the fine structure and phagocytic activity of the capillary endothelial cells in the adrenal cortex which had been histologically considered as phagocytic and placed into the category of the reticuloendothelial system. The endothelial cells in the adrenal cortex were not phagocytic. The cells showing marked phagocytic activity to injected Fe particles were not the endothelial cells but perivascular histiocytes. The reasons why the phagocytic cells in the adrenal cortex had been mistaken for the endothelial cells were considered as follows: endothelial cells are so thinly flattened with numerous fenestrations and the histiocytes are situated so close to them that light microscopic investigations can scarcely identify the 2 kinds of cells; since neither basement membrane nor collagenous fibers are present in the spaces between the endothdlial cells and the histiocytes, the conventional Ag impregnation method which has been utilized until now has little value in the cell identification. Therefore, the endothelial cells of the adrenal cortex should be excluded from the reticuloendothelial system.