The endothelium

The adult human body contains at least one trillion endothelial cells, which weigh more than 100 g and cover a surface area of more than 3000 square meters

Think of the endothelium not only as an inert blood container but as a vast endocrine gland. It stretches over the entire vascular tree with a surface area of about 400 square metres, of which most are in the capillaries. Its weight in an adult is about 1 ·5 kg and it contains an estimated 1 ·2 trillion endothelial cells

it has become evident that the endothelium is by no means a passive inner lining of blood vessels. This 'organ' with a large surface (approximately 350 m2) and a comparatively small total mass (approximately 110 g) is actively involved in vital functions of the cardiovascular system, including regulation of perfusion, fluid and solute exchange, haemostasis and coagulation, inflammatory responses, vasculogenesis and angiogenesis.

The endothelial lining of blood vessels presents a large surface area for exchange of materials between blood and tissues, and is critically involved in many other processes such as regulation of blood flow, inflammatory responses and blood coagulation. It has long been known that the luminal surface of the endothelium is lined with a glycocalyx,

The endothelial cell reacts with physical and chemical stimuli within the circulation and regulates hemostasis, vasomotor tone, and immune and inflammatory responses. In addition, the endothelial cell is pivotal in angiogenesis and vasculogenesis. Endothelial cell injury, activation or dysfunction is a hallmark of many pathologic states including atherosclerosis, loss of semi-permeable membrane function, and thrombosis. Cell facts: (1) Endothelium consists of approximately (1-6) x 10(*13) endothelial cells forming an almost 1 kg organ. (2) They uniquely contain Weibel–Palade bodies, 0.1 μm wide, 3 μm long membrane-bound structures that represent the storage organelle for von Willebrand factor (vWF). (3) The endothelial cell is not only a permeability barrier but also a multifunctional paracrine and endocrine organ. It is involved in the immune response, coagulation, growth regulation, production of extracellular matrix components, and is a modulator of blood flow and blood vessel tone.