Where are the veins in the systemic circulation?
In the legs, the veins are split into two main systems. The deep venous system of the legs are the veins that are deep within the muscle of the lower leg and thigh. These veins lie very close to the arteries that supply blood to the leg and foot. They are acted on directly by muscle movement and are the major pump of venous blood out of the leg. Research shows that approximately 90 to 95% of venous blood in the leg is pumped by the deep vein system.
Of course the skin and subcutaneous fat also is living tissue and therefore has venous blood to be removed once oxygen and nutrition has been supplied to it. It only accounts for approximately 5 to 10% of the venous blood from the leg, but when things go wrong it is clear that this is still a significant amount. The veins that drain these superficial structures are called the superficial veins of the legs. These veins lie in a branching network between the skin and subcutaneous fat. Little veins collect blood from the capillaries joining together in a series of junctions, eventually emptying blood into one of the major venous trunks – the Great Saphenous Vein (GSV) or Small Saphenous Vein (SSV) or sometimes into one of the more minor venous systems such as the Anterior Accessory Saphenous Vein (AASV) or perforating veins.
The Great Saphenous Vein (GSV) and the Small Saphenous Vein (SSV) both drain their blood directly into the deep venous system at specialised junctions – the Great Saphenous Vein via the sapheno-femoral junction (SFJ) at the groin and the Small Saphenous Vein via the sapheno-popliteal junction (SPJ) behind the knee. The minor systems such as the Anterior Accessory Saphenous Vein and the perforating veins all drain their venous blood into the deep veins via their own little junctions. Plus the whole of the superficial venous system drains blood from superficial tissues, runs in the superficial fat, and transmits all of its blood into the deep venous system to be pumped back to the heart.