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11 Surprising Facts About the Circulatory System

Living in space affects the circulatory system

international space station

(Image credit: NASA)

Here on Earth, a person's blood tends to pool in the legs because of gravity (the leg veins have valves that help to maintain blood flow from the legs back up to the heart).

Things are different in space. Blood instead pools in the chest and head (a phenomenon called fluid shift), causing astronauts to have stuffy noses, headaches and puffy faces. This fluid shift also causes the heart to enlarge so it can handle the increased blood flow in the area surrounding the organ.

Even though the body has the same amount of fluid as before, the brain and other body systems interpret the fluid shift as a sudden increase in overall fluid. In response, the body uses several different processes to get rid of excess fluid, resulting in an overall reduction in circulating blood volume.

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Joseph Castro
Joseph Bennington-Castro is a Hawaii-based contributing writer for Live Science and Space.com. He holds a master's degree in science journalism from New York University, and a bachelor's degree in physics from the University of Hawaii. His work covers all areas of science, from the quirky mating behaviors of different animals, to the drug and alcohol habits of ancient cultures, to new advances in solar cell technology. On a more personal note, Joseph has had a near-obsession with video games for as long as he can remember, and is probably playing a game at this very moment.