The systemic blood vessels are defined here as those large vessels supplying and draining regions of the body which include several different organs and tissues. As such, they include the aorta, carotid, subclavian, major splanchnic, and iliac arteries, as well as the caval, brachiocephalic, jugular, subclavian, large abdominal, and iliac veins. Although these vessels serve primarily as major conduits carrying blood to and from the heart, they have a number of other important functions. For example, the elastic nature of the walls of the aorta and the proximal segments of the major distributing arteries have a “Windkessel” effect, stretching to accommodate blood ejected from the left ventricle and recoiling to force blood into the smaller arteries when the aortic valves close. Furthermore, the balance of distribution of the cardiac output to different regions of the body is determined, in part, by the relative diameters of large supplying arteries such as the external carotid or superior mesenteric arteries. Finally, variation in the capacitance of the large systemic veins can actively affect venous return.