Blood Flow in veins

The average pressure in the veins is about 2 mm Hg which is insufficient to return blood to the heart particularly from the lower limbs (against gravity). Venous return therefore requires assistance from:

1. The skeletal muscle pump
2. The thoracic pump

One structural modification which assists blood flow in veins is the presence of valves. These are pocket-like foldings of the tunica intima and ensure that blood flow in veins is in one direction ( towards the heart ). The number of valves increases towards the periphery.