ABSTRACT

Throughout the body, the vasculature is lined with a thin, continuous sheet of endothelial cells. This monolayer of tightly adhering cells regulates-in addition to a broad spectrum of other processes-the barrier properties of the vascular wall. The endothelial barrier allows extravasation of water, electrolytes, proteins, monocytes, and leukocytes to supply the surrounding tissues. The balance between barrier function and regulated extravasation results from stringently controlled permeability of the endothelial monolayer, which prevents excessive vascular leak and interstitial edema. Endothelial permeability is regulated at various levels, and is determined by environmental conditions, such as infl ammation and hypoxia, and the location of the endothelium in the body.