The leg veins are blood vessels (conduits through which blood flows) that run through the entire leg or part of the legs. The veins are the blood vessels that are responsible for the flow of deoxygenated blood from the tissues of the body to the heart. The veins in the legs are classified into two major groups: superficial veins and deep veins.
Superficial Veins of the Leg
The great saphenous vein and the small saphenous vein are the two main superficial veins of the leg. Both these veins communicate with each other through channels or branches known as anastomoses. The branches of the great saphenous vein and small saphenous vein may also join to form an accessory saphenous vein in some cases. These superficial veins also pass blood to the deep veins of the legs via the perforating veins.
Great saphenous vein
The great saphenous vein is formed in the foot by the joining of the dorsal venous arch and the dorsal vein of the big toe. This superficial vein runs up the anteromedial part of the leg to join the femoral vein in the inner part of the upper thigh region. Before joining the femoral vein, the great saphenous vein courses through the saphenous opening in the fascia of the upper thigh.
Blood from the external pudendal vein, superficial epigastric vein, superficial circumflex iliac vein, and the anterior and lateral cutaneous veins also drain into the great saphenous vein. To prevent the backflow of blood, the great saphenous vein contains around 10-12 valves. Many of these venous valves are located just below the level of the perforating vein in the lower leg.
Small saphenous vein
The small saphenous vein also begins in the foot region. It is formed by the convergence of dorsal venous arch and the dorsal vein of the little toe on the lateral side of the foot. After its formation, the small saphenous vein runs behind the lateral malleolus and travels up the back of the lower leg by penetrating the deep fascia. It runs between the heads of the gastrocnemius muscle, eventually reaching the region behind the knee (also known as popliteal fossa), where it empties into the popliteal vein. The small saphenous vein also communicates with both the great saphenous vein and the deep veins of the leg.
Deep Veins of the Leg
There are three major deep veins that run alongside the major arteries in the lower limb. The deep veins of the leg also receive blood continuously from the superficial veins. The blood from the deep veins ultimately drains into the popliteal vein that lies behind the knee region.
The popliteal vein, in turn, drains blood into the femoral vein in the thigh region. The blood from the thigh muscles is carried by the perforating veins that drain into the profunda femoris vein of the thigh. The profunda femoris also drains into the femoral vein.
Anterior tibial vein
Anterior tibial vein originates and receives blood from the dorsalis pedis vein in the foot.
Posterior tibial vein
The posterior tibial veins receive blood from the lateral and medial plantar veins.
The fibular veins drain blood from the lateral compartment of the leg into the posterior tibial vein.
How does blood flow in the leg veins?
The long distance between the heart and the tissues of the legs make returning the blood to the heart a difficult endeavor. The flow of blood towards the heart is also counteracted by the effects of gravity, which pulls the blood downward into the limbs.
To counter the effects of gravity, two special mechanisms work in the venous system of the legs to make the blood flow towards the heart possible. These two systems are the pumping action of the muscles in the leg and the presence of venous valves.
The blood from the feet is collected by the superficial veins and emptied into the deep veins and the femoral vein. The deep veins are located beside the arteries of the leg. These veins also pass between the muscles of the legs. The contraction of the muscles in the lower leg (e.g., the gastrocnemius muscle) during leg movements pushes the blood up through the veins.
This effect is referred to as the musculovenous pump. For the musculovenous pump to work effectively, one must move frequently throughout the day. Sedentary activities like sitting, lying down or standing in one spot for a long time can cause pooling of the blood in the veins of the lower limbs.
Apart from the muscular contractions in the lower leg, the pulsatile flow of blood through the adjacent arteries in the legs also aid blood flow through the veins of the lower leg.
Valves are flaps of tissue that are located inside the veins. These valves are designed to open only in one direction, thereby preventing any backward flow of the blood. When the valves in the veins of the legs become weak, they are not able to prevent the backward flow of blood. This condition, known as valvular insufficiency, leads to pooling of the blood in the veins of the lower leg. This causes the appearance of engorged and tortuous veins known as varicose veins.
The veins of the legs are responsible for the flow of deoxygenated blood from the limb tissues to the heart. Any condition that impairs the return of the deoxygenated blood from the legs to the heart is referred to as venous insufficiency. The most common cause of venous insufficiency is dysfunction of venous valves. Incompetence of the venous valves in the leg causes backward flow of blood (also referred to as venous reflux).
Venous blood flow towards the heart could also get hampered due to the presence of some blockage in the veins (such as the presence of a blood clot). Venous insufficiency causes pooling of the blood in the veins of the lower limbs. Over time, the flow of blood through the veins of the legs becomes sluggish. This is referred to as venous stasis.
The sluggish movement of blood in the veins of the lower limbs further increases the chance of blood clot formation. A breakaway clot resulting from such a condition can be potentially lethal as it can cause pulmonary embolism. The two most common conditions associated with venous insufficiency are varicose veins and formation of blood clots (or thrombus) in the leg.
Varicose veins refer to engorged and tortuous veins that are a result of pooled blood. It is caused mainly by inactivity. A thrombus or blood clot can cause both partial and complete obstruction to blood flow in the veins of the legs. Blood clot in the deep veins of the legs is referred to as deep vein thrombosis.