Vascular Physiology and Pharmacology

The vascular wall is composed of three layers with three distinct functions. The innermost layer is the endothelium which is in direct contact with the blood and humoral factors. It acts as a barrier to blood-borne materials and as an endocrine organ producing both paracrine and endocrine substances. The function of the major products of the endothelium on vascular wall is discussed. The middle or medial layer is composed of vascular smooth muscle and the tone of this muscle is a major regulator of systemic blood pressure and flow. The major regulators of vascular smooth muscle tone are intracellular calcium and the degree of calcium sensitivity of the contractile elements. Endogenous regulators of these two parameters are discussed. The outermost layer of the vascular wall is the adventitia composed of adventitial fibroblasts and inert connective tissues. This layer provides structural support and acts as an endocrine organ producing various vasoactive factors including reactive oxygen species (ROS) and growth factors. The structure, function, and cellular composition of each layer are discussed.