The cardiovascular system of the leg and foot includes all of the blood vessels that provide blood flow to and from the tissues of the lower limb. These blood vessels supply vital oxygen and nutrients to support cellular metabolism in the lower limb while transporting carbon dioxide and metabolic wastes back to the trunk to be removed from the body. Large volumes of deoxygenated blood are stored in the veins of the lower limbs as a reservoir for the rest of the body. Blood flow also helps to maintain the homeostasis of body temperature by delivering hot blood from the trunk to the tissues of the extremities.
Oxygenated blood from the heart passes through the aorta as it descends through the thorax and abdomen and into the pelvis. In the pelvis, the aorta splits into the left and right common iliac arteries that descend toward the legs. The common iliac arteries further divide into the internal and external iliac arteries, with the external iliac artery being significantly larger than the internal iliac. Several branches of the external iliac artery extend into the abdominal, groin, and pelvic regions, but the bulk of its blood continues onward into the leg, where it becomes known as the femoral artery.
In the thigh, the femoral artery carries blood to the skin and muscles through several smaller branches that spread throughout the femoral region. As the femoral artery descends through the thigh, it enters the popliteal region in the posterior of the knee and becomes known as the popliteal artery. Several branches of the popliteal artery spread through the tissues of the knee to provide blood to this region, but most of the blood flow continues into the lower leg.
In the lower leg, the popliteal artery divides into three major branches: the anterior tibial artery, posterior tibial artery and fibular (peroneal) artery. Each of these arteries delivers blood to the leg and continues into the foot, with the posterior tibial and fibular arteries forming the plantar arteries and plantar arch that supply blood to the bottom of the foot and toes. The anterior tibial artery forms the arcuate artery and its many branches to supply blood to the top of the foot. A vast network of anastomoses forms between the arteries in the foot to provide redundant connections in case a blood vessel becomes blocked.
Deoxygenated blood returning from the tissues of the feet is collected by many veins that join to form the dorsal venous arch on the top of the foot and the deep plantar venous arch of the sole of the foot.
Blood from the dorsal venous arch passes into three major veins in the leg: the small saphenous, great saphenous, and anterior tibial veins. The great saphenous vein ascends through the leg and thigh on the medial side, collecting blood from tissues in these regions. On the lateral side, the small saphenous vein ascends through the leg collecting deoxygenated blood before passing posterior to the knee. The anterior tibial vein forms a small network anterior to the tibia and collects blood from the tissues of the shin.
The plantar venous arch sends its blood into the leg through the medial and lateral plantar veins into the posterior tibial vein, which ascends along the leg posterior to the tibia. The posterior tibial vein collects blood from the posterior leg and merges with the fibular vein that drains blood from the lateral side of the leg. In the popliteal region posterior to the knee, the small saphenous, anterior tibial, and posterior tibial veins join with several smaller veins of the knee to form the popliteal vein.
In the femoral region, the popliteal vein continues to receive blood from the tissues of the thigh and becomes the femoral vein. The femoral vein ascends parallel and lateral to the great saphenous vein; these merge along with many smaller veins at the groin to form the external iliac vein. Blood passing through the external iliac vein continues onward into the common iliac vein and inferior vena cava, which returns it to the heart.
Blood flowing through the veins of the lower limbs is under very little pressure and must fight the pull of gravity to return to the heart. To combat this blood flow problem, veins contain many one-way valves, which permit blood to flow only toward the heart. Muscular contractions within the feet and legs exert pressure on the veins to push blood through the valves and toward the heart. When the muscles relax, the valves prevent the blood from moving away from the heart. Sometimes the valves in the legs become worn out, allowing the blood to collect and ballooning the walls of the vein. This phenomenon is known as a varicose vein.