ABSTRACT

Endothelium refers to the simple squamous epithelium that is found lining organs, blood vessels and body cavities. This single layer of cells lies on top of a basement membrane, and in small arteries, arterioles and glands it is also in proximity to smooth muscle. The major types include: continuous endothelium; fenestrated endothelium and discontinuous endothelium. Endothelium is a highly sophisticated and cellularly active tissue with essential roles in coagulation, inflammation and vasomotor tone. Endothelial structure varies according to its site and function. The endothelial lining at the alveolar–capillary interface plays an important role in the diffusion of gases and lipid-soluble agents. In the blood–brain barrier the tightly anchored endothelial cells form a relatively impermeable barrier that protects the central nervous system. Endothelium releases several vasoactive substances that are crucial in regulating vascular smooth muscle tone. Vascular endothelium can synthesise several prostaglandins with prostacyclin being the major derivative.