Are all of your veins like little tiny loops where blood flows through, then back to the heart, or does blood sort of push and pull it’s way back and forth through your body? Basically, how the heck does the cardiovascular system work?
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Many veins, particularly those in the arms and legs, have one-way valves. Each valve consists of two flaps (cusps or leaflets) with edges that meet. Blood flowing toward the heart pushes the flaps open like a pair of one-way swinging doors. If gravity or muscle contractions try to pull the blood backward or if blood begins to back up in a vein, the flaps are pushed closed, so the blood does not flow backward. Thus, valves help the return of blood to the heart—by opening when the blood flows toward the heart and closing when blood might flow backward.
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