The Venous System

The venous system not only serves as a conduit for the return of blood from the capillaries to the heart but also provides a dynamic, variable blood storage compartment that influences cardiac output. The systemic venous system contains more than 75% of the blood volume of the entire systemic circulation. The conduit characteristics of the venous system primarily depend on the anatomy of the system. Valves in the veins of the limbs are crucial for reducing the pressure in dependent parts of the body. The stressed volume is the volume of blood in the vascular system that must be removed to change the computed transmural pressure from its prevailing value to zero transmural pressure. Using plethysmography, a rigid container is placed around the organ, and a servo system functions to change the fluid volume in the chamber to maintain the chamber pressure constant.