ARTERIAL ANATOMY, PHYSIOLOGY, AND PATHOLOGY Cross-section histological examination of arteries reveals 3 concentric regions: the intima, media, and adventitia (Fig. 1 A). The boundaries of the intima from the luminal to abluminal sides include the endothelium, a surface monocellular layer with extraordinary biochemical properties, a basement membrane, and the final layer before the media, the internal elastic lamina. The intima is normally extremely thin with endothelial cells in alignment with the direction of flow, except in areas of flow disturbance, such as bifurcations or branches. Normal endothelium is an organ system intimately involved in local vascular regulation. Nitric oxide is produced by endothelial cells and is antithrombogenic, antiproliferative, and vasodilating. Normal endothelial cells also have synthetic capability for endothelin, which is a powerful vasoconstrictor and is promitogenic, and for the vasodilator prostacyclin. Numerous surface receptors are present, including low density lipoprotein receptors.