The ongoing flow of blood from the heart to the body and back to the heart again is called circulation. Blood vessels carry blood throughout your body. Veins are the vessels that return blood to the heart.
Three Types of Veins
Superficial veins collect the blood just beneath the skin
Perforating veins carry blood from the superficial veins to the deep veins
Deep veins run through the muscles and carry 90 percent of the blood back to your heart
Anatomy of a vein
Veins have cup-like flaps called valves spaced along their inside walls. Valves open upward, so blood can move up the vein. Valves close to keep blood from falling back down the vein.
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