Venous return flow
In contrast to the arteries, the veins have a low pressure. This means that the blood from parts of the body that lie below the heart level cannot be pumped back to the heart against gravity as easily. To facilitate this venous return, all large veins below the heart level have venous valves.
Venous valves are folds of the innermost layer (tunica intima, endothelial layer), which are additionally supported by collagenous fibrous tissue. The venous valves can prevent a reversal of the direction of blood flow, since venous valves only allow the blood to pass in one direction at a time, namely back to the heart. If blood flows in the opposite direction to that in which it should flow (standstill), the venous valves inflate like small valve sails, lie close together and thus close the vein.
The contraction of muscles allows venous blood to be pumped to the next venous valve level. This is because many veins are fused with muscles. If the muscle now tenses, contracts and becomes thicker as a result, the sheath of the muscle (fascia) that surrounds the muscle and is fused with the veins becomes tense. This exerts pressure on the blood-filled vein and since the venous valves only allow one direction of blood flow, the blood flows further back to the heart.
Other pumping mechanisms of the veins
Many everyday movements of our body promote the venous return flow of blood. When running and walking, the pressure of the occurrence at each step forces the blood out of the veins of the blood towards the heart. Frequently, arteries and veins also lie directly next to each other. The pressure pulse in the arteries causes compressions in the veins, which also pushes blood back to the heart. The heart also plays a decisive role in venous return flow.By shifting the valve plane in the heart with every heartbeat, the heart sucks venous blood into the right chamber (right ventricle, ventriculus dexter) with little force.
