The low pressure in the veins is therefore a problem for the return of blood to the heart. And it's even more complicated for leg veins due to longer journey and real gravity.

Fortunately, nature has done things right.

Our veins are equipped with valves every 4 to 5 cm that force the blood back to the heart and prevent it from going down (this corresponds to anti-reflux valves). Other mechanisms also facilitate venous return. Compression of plantar arch and contraction of the calf muscles push blood upward. The respiratory movements also facilitate the work.

Some figures

• Our body contains about 5 liters of blood
• Every day, our heart pumps 8,000 gallons of blood
• It beats an average of 70 times per minute
• And each contraction expels about 75 ml of blood into the aorta
• Some 100,000 km of blood vessels carry blood throughout the body... That is more than two times around the earth, if they were placed end to end!