Introduction

Figure 1: Schematic representation some of the receptors on the endothelial cell and substances secreted that have vasomotor effects. In the left upper corner the selectins which play a role in leucocyte rolling, and adherence. In the right upper corner the receptors that stimulate NO release. In the right lower corner a synopsis of substances secreted by the endothelial cell with vasomotor functions. And in the left lower corner members of the immuno-globulin superfamily ICAM-1,2 and VCAM-1 that play a role in leucocyte adherence and transmigration.

The endothelium is a widespread organ, covering an area of about 1000 m². The cells of the endothelium cover the internal surface of the blood vessels, heart, aorta, arteries, arterioles, capillaries, venules and veins. The endothelium was formerly thought of as a fairly inert layer of cells whose main function was a barrier between blood and interstitium to trans-vascular diffusion of liquids and solutes. Other functions discovered for the endothelium include, control of the mechanics of blood flow by secretion and modification of vasoactive substances with contraction and relaxation of smooth muscle, regulation of coagulation, leucocyte adhesion and vascular smooth muscle cell growth. Some of the receptors expressed on and substances secreted by endothelial cells are shown in figure 1.

Dysfunction of the endothelium is present when there is an inappropriate alteration with respect to preservation of organ function. Manifestations of endothelial dysfunction include changes in; leucocyte endothelial interaction, vascular permeability, vasomotor functions and apoptosis and necrosis. The main clinical areas where endothlelial dysfunction appears to play an important role are, ischaemia-reperfusion, endotoxemia, diabetes, immunological rejection and dyslipidaemia.