Ultrastructural mechanisms of transendothelial transport in blood vessels

: The author describes a series of structural aspects of transendotheliumiumial transport on the basis of literary data, printed in journals and coming from well known foreign laboratories. He reports data on three types of endothelium--uninterrupted, fenestrated and interrupted. He indicates the ways of transfer of lipid-soluble substances and ultrastructural devices for transfer of water and water-soluble substances. These devices are divided into two groups-universal (vesicular structures, intercellular slits), which are characteristic of the three types of endothel and specific (fenestra and pores), characteristic of fenestrated and interrupted endothel respectively. The author presents a series of actual questions about vesicular transport-nature and movement of micropinocytotic vesicules, structure, permeability and orientation of transendothelial canals. He describes data on possibility of intercellular slits as sites for passive transport of water and water-soluble substances. He indicates distribution and structure of binding complexes between endothelial cells, limiting permeability of intercellular contacts. The structure and permeability of fenestra and pores are presented as sites of passive transport, but those of the pores-for active passage of cellular elements as well. Various ultrastructures, connected with endothelial permeability, are surveyed as morphologic equivalents of the small or large pores by the physiological theory of pores.