Non-return valves in the legs
Veins have crescent-shaped valves at intervals that divide vessels into segments. These valves open as soon as the blood is pressed upwards towards the center of the body against gravity and close in the instant that the blood comes to a "standstill" and would start to flow backwards.
Defective venous valves
Intact valves prevent the blood from pooling in the periphery (particularly when standing) and absorb the forces that act on the veins under stress (walking, jogging and jumping). The communicating veins also possess valves that prevent return flow from the deep to the superficial venous system.
If the functionality of the valves is impaired, or has even been destroyed, by injury or after inflammation, the work performed by the leg muscles sometimes presses the blood towards the heart in the subcutaneous veins instead of in the deep veins. This results in over strain of the superficial venous system. The symptoms of this are stasis and edema, in the long term this can develop into chronic venous insufficiency (CVI).
Once damaged, venous valves remain defective. However, valves that have only lost their function can regain their functionality, at least in part, with consistent compression treatment.
Calf muscle pump - The venous valves determine the direction
Every time the muscles contract, they squeeze the deep veins in the legs together and transport the blood further. Here too, the venous valves determine the direction of flow and stop the blood flowing backwards.
Hiking, climbing stairs, cycling or swimming keep the muscle pump fit and ensure good circulation to the legs.
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The heart as the hub
The heart is the hub between the two circulatory systems in the body. The heart is a so-called "hollow muscle" that is divided into a left and a right side separated from one another by the septum.
In the smaller pulmonary circulation, the deoxygenated blood is transported from the right ventricle through the pulmonary artery into the lungs, where it is enriched with oxygen before it flows along the pulmonary veins into the left atrium. From here, it is pumped through the left ventricle and the aorta into the large somatic circulation.
The widely branching somatic circulation supplies all the organs and regions of the body with oxygen-rich blood. The used blood (low in oxygen) flows back in the veins towards the heart against gravity, where it passes through the superior vena cava and back into the right atrium. From there, the cycle starts all over again.
The two circulatory systems are connected to each other and only function as long as they work in parallel. It is noteworthy that the pressures in the two circulatory systems differ. The fact that the pressure in the vessels of the somatic circulation is higher than in the pulmonary circulation is due to the differing blood volumes.
The heart is about 4-5 inches long and approximately 3.5 to 4.5 inches wide. It can hold about 20 to 40 ounces of blood and weighs on average three-quarters of a pound. The blood volume transported each time the heart muscle contracts at rest (stroke volume) amounts to approximately 2.5 ounces.