[The morphological bases of transcapillary metabolism in the adrenal cortical layer]

Capillaries of the cortical substance in the white rat adrenals have been studied by means of electron microscopic and tracing methods. Two types of interendothelial contacts-the adhesive and occlusive have been described. Owing to the identification of the open and close micropyknocytic vesicles, it has been stated that the vesicular transport through endothelium takes place simultaneously in both directions. Transendothelial canals occur rather seldom. Molecules of ferritin get into them. Fenestrae occupy the greater part of the endothelial cells. Position and size of the fenestrae are described, as well as the structure of their diaphragm. The fenestrae have been stated to be permeable for molecules of ferritin. Owing to their structural peculiarities and the experiments on ferritin administration, the interendothelial contacts are identified as structural equivalents of small pores, previously described by physiologists, and the micropyknocytic vesicles, transendothelial canals and fenestrae-as structural equivalents of large pores. At some small areas, the endothelium can be interrupted, evidently, as consequence of certain rearrangements of the fenestrated area resulted from an increased transcapillary transport.