Anatomy, Arterioles

Excerpt

Oxygenated arterial blood circulates through the body via the vascular tree consisting of sequentially smaller arteries, arterioles, and capillary beds. Nutrients and waste exchange between the blood and body tissues occurs at the capillary bed. Venules serve as exit vessels in the capillary bed of various organs and unite to form veins, which return the blood to the heart. The arteriolar wall consists of 3 layers of cellular and extracellular components. The intima contains endothelial cells on a basement membrane; the tunica media consists of internal elastic lamina and layers of smooth muscle; and the outer adventitia is made mainly of collagen, nerve endings, and fibroblasts. Arterioles contribute to maintaining mean arterial pressure and tissue perfusion as they are the important sites of total peripheral resistance. By increasing or decreasing the diameter, they also play a principal role in regulating blood flow in an organ or tissue-specific manner.