ABSTRACT
The primary purpose of the venous circulation is to return blood to the heart for reoxygenation and recirculation. Understanding volume and pressure relationships is essential for understanding normal and abnormal venous function. The enormous capacity of the venous reservoir plays a major role in the maintenance of cardiovascular homeostasis by accommodating volume shifts. Regulation of venous tone is an important aspect of volume accommodation and works in concert with arterial control mechanisms that effect changes in the distribution of cardiac output. Venous return is defined as the rate of blood flow toward the heart, which in homeostatic circumstances must equal cardiac output. Venous return is enhanced by negative and neutral intra-abdominal and intrathoracic pressures. Venous return from the dependent lower extremity is achieved by active pumping of the calf muscle assisted by competent venous valves. Understanding the normal venous circulation requires mastery of complex hemodynamic and physiologic concepts.
