Endotheelbarrière

Endotheelbarrière, also known as the endothelial barrier, is the selective boundary formed by the endothelial cells lining the interior of blood vessels that regulates the exchange of fluids, solutes, and cells between the bloodstream and surrounding tissues. Its permeability is controlled by intercellular junctions, the glycocalyx coating on the luminal surface, and the underlying basement membrane, with additional support from pericytes in microvessels and astrocytic endfeet in the brain.

Key structural elements include tight junctions comprising claudins, occludin, and junctional adhesion molecules, and adherens junctions formed by VE-cadherin, along with the cytoskeleton. These components govern paracellular and, to a lesser extent, transcellular transport. The barrier also features a glycocalyx layer that modulates interactions with circulating cells and molecules.

Functions of the endotheelbarrière include maintaining vascular tone and fluid balance, restricting random diffusion of large molecules, and coordinating leukocyte trafficking during immune responses. The barrier’s properties vary by vessel and tissue; the blood-brain barrier is highly restrictive, while fenestrated and sinusoidal endothelia in organs like the kidney and liver are more permeable.

Regulation involves chemical mediators such as VEGF, histamine, and inflammatory cytokines, as well as mechanical forces like shear stress. Dysfunction or disruption of the barrier contributes to edema, organ dysfunction, and disease processes such as sepsis, acute respiratory distress syndrome, diabetic retinopathy, and tumor-associated vascular leakage.

Clinical relevance includes strategies to protect or restore barrier integrity and challenges related to drug delivery to protected sites like the brain. Experimental assessment often uses transendothelial electrical resistance and tracer permeability assays.