Veins are a critical feature of the body's circulatory system, which is made up of about 60,000 miles of vessels that service trillions of living cells. About 7,200 quarts of blood pass through the heart every 24 hours. While the job of the arteries is to distribute oxygen-rich blood throughout the body, the veins carry oxygen-depleted blood back to the heart, which then pumps it into the lungs to pick up more oxygen. The newly oxygen-enriched blood is then sent back to heart and pumped back out into the body.
There are two main types of veins. Deep veins are the main motorways for blood flow, draining most of the blood, while superficial veins are the ones closest to the skin -- such as the thin blue lines often visible on your hands. There are two main superficial veins. The long saphenous vein runs from the ankles to the groin on the inside of the legs, while the short saphenous vein runs from the ankles to the backs of the knees on the outside of the legs.
By the time blood reaches the veins, the force of the heartbeat is weak, and the blood must struggle against the pull of gravity to move up from the feet to the heart. The muscles in the feet and calves contract and relax as a person walks, and this squeezes the veins to help the blood move up the leg. Also assisting the veins in overcoming the downward pull of gravity are a series of one-way valves inside them, which can open to allow blood to flow up the vein, and then close to prevent it from flowing back down. That's why when we stand up, the blood in the veins doesn't run down into our feet.
What are varicose veins?
Varicose veins appear when the veins near the skin get bigger and the valves controlling blood flow break down. The blood doesn't flow up the vein as efficiently, and can sometimes flow back down, causing uncomfortable pressure. When someone with varicose veins stands up, the veins become more visible or lumpy.