JEANETTE ENGQVIST / SCIENCE PHOTO LIBRARY JEANETTE ENGQVIST / SCIENCE PHOTO LIBRARY
Skeletal-muscle pump. Computer illustration demonstrating how movement of the lower leg helps to pump blood (red) back up the body through the veins. A collection of muscles around the deep veins of the lower leg compress the veins during movement of the leg. This squeezes the blood through the veins, which is prevented from returning by the one-way valves (white arrows) in the veins.
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