Abstract
The vascular endothelium, a monolayer of endothelial cells (EC), constitutes the inner cellular lining of arteries, veins and capillaries and therefore is in direct contact with the components and cells of blood. The endothelium is not only a mere barrier between blood and tissues but also an endocrine organ. It actively controls the degree of vascular relaxation and constriction, and the extravasation of solutes, fluid, macromolecules and hormones, as well as that of platelets and blood cells. Through control of vascular tone, EC regulate the regional blood flow. They also direct inflammatory cells to foreign materials, areas in need of repair or defense against infections. In addition, EC are important in controlling blood fluidity, platelet adhesion and aggregation, leukocyte activation, adhesion, and transmigration. They also tightly keep the balance between coagulation and fibrinolysis and play a major role in the regulation of immune responses, inflammation and angiogenesis. To fulfill these different tasks, EC are heterogeneous and perform distinctly in the various organs and along the vascular tree. Important morphological, physiological and phenotypic differences between EC in the different parts of the arterial tree as well as between arteries and veins optimally support their specified functions in these vascular areas. This review updates the current knowledge about the morphology and function of endothelial cells, particularly their differences in different localizations around the body paying attention specifically to their different responses to physical, biochemical and environmental stimuli considering the different origins of the EC.
Highlights
The vascular endothelium is the inner-most structure that coats the interior walls of arteries, capillaries and veins
endothelial cells (EC) are polarized cells: their luminal membrane is directly exposed to blood constituents and circulating cells, while the basolateral surface is separated from surrounding tissues by a glycoprotein basement membrane which is secreted and anchored to their cell membrane by EC themselves
Studies could show that endothelium-derived hyperpolarization factor (EDHF) appears to become the predominant endothelium-dependent vasorelaxation pathway, in the absence of the endothelial
Summary
The vascular endothelium is the inner-most structure that coats the interior walls of arteries, capillaries and veins. Endothelial cells (EC) were described to anchor to an 80-nm-thick basal lamina (BL). Both EC and BL constitute the vascular intima, establishing a hemocompatible surface, estimated a total combined surface area of 3000–6000 m2 in the human body, comprising 1 to 6 × 1013 EC [1,2]. From their first description in 1865 until the early 1970s, this monolayer was regarded as a mere inert barrier separating blood cells from the surrounding tissue.
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