Venous return = arterial outflow (William Harvey, 1628)

Hold 60 - 70% of body's blood volume

Blood pooling occurs below heart level

Valves in deep muscle and cutaneous veins

CNS control of venomotion

Usually collapsed above heart level

Flat when empty; pressure approximately zero until x-section is circular, then pressure increases sharply

Capacity for venomotor tone is reduced by bed rest, alcohol, fatigue, etc.

Pulse, retrograde from the heart, in systemic veins