Properties of endothelium

• Functions as a selective permeability barrier (permeability regulator: filter function).

Large molecules: vesicular transport; passage through intercellular junctions Small molecules: vesicles; junctions; and through cytoplasm

• Forms a blood compatible container with a non-thrombogenic surface, which is achieved by the balance between the prothrombotic and the antithrombotic and fibrinolytic characteristics of the endothelial cell.

• Synthesis/metabolism/secretion of:

Vasoactive (vasorelaxing and vasoconstricting) autacoids: prostacyclins; leu-

kotrienes; nitric oxide; endothelin; angiotensin-converting enzyme. Connective tissue components: laminin, fibronectin, vitronectin. Chemokines: monocyte chemoattractant protein-1.

Adhesion molecules: von Willebrand factor, E-selectin, intercellular adhesion molecule-1, vascular cell adhesion molecule-1.

• Binding and internalisation of lipoproteins: modify low density lipoproteins (LDLs)- LDL receptor; lipoprotein lipase.

• Synthesis of stimulating or inhibitory mitogens, with autocrine and paracrine effects.

• Regulator of vascular tone (regulation of smooth muscle contractility) Smooth muscle relaxation: nitric oxide.

Smooth muscle contraction: endothelin; angiotensin II

• Regulator of haemostasis and inflammation: secretes procoagulant factors and inflammatory mediators:

Platelet adhesion and activation: von Willebrand factor; P-selectin; E-selectin;

platelet-activating factor Coagulation: thrombomodulin; heparin sulphate

Characteristics shared by all endothelial cells

Factor VIII/ von Willebrand factor staining; S

Cell-specific surface lectins; l

Uptake of acetylated LDL; Response to angiogenic growth factors.

Vasoactive endothelial products

Endothelium-derived relaxing factors

Nitric oxide Prostacyclin (PGI2)

Endothelium-mediated vasoconstrictors

Endothelin-I Thromboxane Prostaglandin H2 Oxygen free radicals

Fibrinolysis: tissue type plasminogen activator (t-PA); urinary (u)-PA;

plasminogen activator inhibitor Cytokines: interleukins -1, -6 and -8.

• Forms growth-regulating molecules: platelet derived growth factor; fibroblast growth factor; tissue growth factor beta.

• Forms connective tissue macromolecules (matrix factors): collagen; proteoglycans.

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