ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Venous system. Computer-enhanced engraving of the venous system in the human body. Veins carry deoxygenated blood back to the heart from the rest of the body. Unlike arteries, veins rely on valves and muscular body movements to push the blood along. The average adult has about five litres of blood in the body. Original illustration from "De Humani Corporis Fabrica" (1543) by Andreas Vesalius.
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