endoteelille

Endoteeli, or endothelium in English, is the thin cellular layer lining the interior surface of blood vessels, lymphatic vessels, and heart chambers. It forms a continuous monolayer between the bloodstream and surrounding tissues, acting as a dynamic interface that regulates exchange and vascular function.

Endothelial cells sit on a basement membrane and vary in structure across tissues. In most vessels they form a continuous lining; in fenestrated capillaries of the kidney and intestines, and in discontinuous endothelium of the liver, spleen, and bone marrow, endothelial gaps increase permeability. A surface coat called the glycocalyx covers many endothelial cells and participates in barrier function and mechanotransduction.

Functions include regulation of vascular tone by releasing relaxing and contracting factors such as nitric oxide and endothelin; control of coagulation and fibrinolysis; modulation of inflammation through adhesion molecules and cytokines; and mediation of leukocyte trafficking. The endothelium also supports angiogenesis and the exchange of nutrients, gases, and waste between blood and tissues.

Endothelial cells arise from mesoderm and form vessels through vasculogenesis and angiogenesis, with maintenance guided by shear stress. Dysfunction or injury to the endothelium is associated with cardiovascular diseases, diabetes, hypertension, and inflammatory states, and therapies often target endothelial health and nitric oxide signaling.