Veins and Their Control

Abstract

THAT the venous system contains the greater part of the circulating blood volume and functions as the reservoir of the circulatory system has been evident for years. We are now aware that the veins are not a system of passive tubes; the smooth muscle in their walls can be activated by the sympathetic nerves and by circulating substances. Venoconstriction raises the pressure in the venous reservoir and consequently raises cardiac filling pressure. Since filling pressure is a prime determinant of cardiac function, the venous system has a major role in the regulation of cardiac output. Recent data indicate that the . . .