[Vascular endothelium--a review. I. General morphology of the vascular endothelium].

The vascular endothelium as a monolayer interposed between blood/lymph and interstitial fluid realizes different functions as continuous circulation of blood/lymph, processes of clotting, fibrinolysis and antithrombotic surface properties, some aspects of defense, inflammation, different synthetic activities, and establishing of exchange pathways and barriers for several substances. This survey will be presented as a sequence of 6 single articles. The 1st one deals with the general morphology of vascular endothelium. Heteromorphism of endothelium means variability of shape and orientation as a result of different functional conditions, mediated by the cytoskeleton. "Contactons" are units of interconnected cells; each cell exhibits 4 zones of different structural and functional specialization: nuclear-, organelle-, peripheric-, and contact zone. Membrane associated structures of the surface are the glycocalix and the subplasmalemmal subcortical layer. Composition and function of these including the plasmalemma itself are explained. Structures formed by the endothelial plasmalemma are vesicles, fenestrations, pores, gaps, and microvilli. Arrangement, function, dynamics, and their relationships to the cytoskeleton are referred including TEM, SEM, and Freeze Etching techniques. Concerning interendothelial contacts, different types of junctions and 4 types of junctional fibrils are described. A short structural description of the basement membrane and of the organelles of endothelium is given. Some new informations of the endothelial cytoskeleton, concerning composition, structure, arrangement, properties, and relationships to other subcellular constituents are presented, completed by impressive SEM-photographs.