The veins of the lower leg can be divided into two groups – superficial and deep. Since the distal parts of the lower limb, i.e. the leg and feet, are the furthest points from the heart compared to any other part of the body, blood has a longer distance to travel bac to the heart.
The pressure of blood in the arterial system drops significantly in the feet as energy is lost along the path of flow. Coupled with the counteracting force of gravity, the leg veins work along with the leg muscles to return blood back to the heart. These leg veins have also developed valves to assist in this process.
The key to returning blood to the heart from the legs lies in joint effect of the musculovenous pump and the venous valves in the veins of the leg.
Musculovenous Pump of the Leg
The superficial veins drain most of the blood from the feet and may empty it directly into the femoral vein although it passes most of the blood into the deep veins via the perforating veins. The deep veins are under the continuous effect of the contracting muscles of the leg which function as a pump, known as the musculovenous pump of the lower limb. This propels blood up the leg until it can empty into large veins like the femoral vein and then travel back to the heart via the iliac veins and inferior vena cava.
The superficial veins are also influenced by the musculevenous pump although not to the extent as the deep veins. Being stationary (sitting, lying flat or even standing at one spot for long periods of time) means that this musculovenous pump cannot work as efficiently to move blood in the leg veins.
Vein Valves in the Leg
Venous valves are designed to prevent the backflow of blood traveling up a vein back to the heart. These valves are flaps (cusps) of the inner lining of the vein (endothelium) that fill up with any blood that attempts to flow away from the heart. This occludes that segment of the vein thereby preventing any blood from flowing backwards.
Essentially these venous valves make the flow of blood unidirectional (in one direction i.e. towards the heart).When these valves are compromised, the blood in the leg does not return back to the femoral vein as efficiently. Depending on the extent of valvular insufficiency, blood may pool in the lower parts of the leg and engorge the veins of the leg.
Superficial Leg Veins
The two major superficial veins of the leg are the great saphenous and small saphenous veins. The great saphenous vein runs along the front inner (anteromedial) part of the leg and thigh until it joins the femoral vein. The small saphenous travels up the back of the lower leg (posterior aspect). During its course, both the great and small saphenous veins freely communicate with each other via smaller collateral channels (anastamoses). Sometimes an accessory saphenous vein will also be present when the multiple tributaries from the small and great saphenous veins unite.
Great Saphenous Vein
This vein is a conjunction of the dorsal vein of the great toe and the dorsal venous arch of the foot. It travels up the leg, in front of the inner ankle protruberance (anterior to the medial malleolus), and ascends all the way up the lower limb on the inner aspect leg and thigh (anteromedial aspect). At the height of the upper thigh, it enters through the saphenous opening of the fascia lata and empties into the femoral vein.
Picture from Wikimedia Commons
The great saphenous vein also receives blood from the :
- anterior and lateral cutaneous veins
- superficial circumflex iliac vein
- superficial epigastric vein
- external pudendal vein
There are some 10 to 12 venous valves in the course of the great saphenous vein. Most of these valves exist in the part of the vein that runs through the lower leg and is located just inferior to where a perforating vein communicates with the great saphenous vein. These perforating veins allow blood to move between the superficial and deep veins of the leg.
Small Saphenous Vein
The small saphenous vein begins on the outer part of the foot (lateral aspect) by the joining of the dorsal vein of the little toe with the dorsal venous arch. It passes behind the the outer ankle protruberance (lateral malleolus) and runs up the back of the lower leg. The small saphenous penetrates the deep fascia, travels up between the heads of the gastrocnemius muscle and empties into the popliteal vein in the popliteal fossa (behind the knee).
Picture from Wikimedia Commons
The small saphenous is in continuous communication with the great saphenous vein via collateral channels. In addition, perforating veins carries blood from the small saphenous vein into the deeper leg veins where it is pushed up the leg by the action of the leg muscles (musculovenous pump of the lower limb).
Deep Leg Veins
The deep veins of the lower limb run alongside major arteries of the leg as it passes superiorly (upwards towards the heart). The deep veins are constantly receiving blood from the superficial veins. There are three main deep veins in the lower leg :
- anterior tibial vein which receives blood from the dorsal venous arch
- posterior tibial vein and fibular vein (also known as the peroneal vein) which form from the medial and lateral plantar veins
These three veins (anterior tibial, posterior tibial and fibular) drain into the popliteal vein in the popliteal fossa (behind the knee). The popliteal vein in turn drains into the femoral vein of the thigh.
Perforating veins of the thigh carry blood from the thigh muscles and drains into the deep vein of the thigh, which is also known as the profunda femoris vein. This also terminates in the femoral vein, which in turn becomes the external iliac vein.
The deep veins of the leg lie between the extensive muscles of the lower leg and thighs. This allows the blood within these veins to be propelled upward by the contraction of these muscles (musculovenous pump of the lower limb). Even the pulsations of the arteries of which the deep veins of the leg run along with helps to propel blood in the veins. The deep veins receive most of the blood from the superficial leg veins, although the great saphenous empties its contents directly into the femoral vein. An occlusion within the deep veins of the leg can therefore impede blood returning from the legs.