What Happens to the Human Body in Space?

Gravity keeps our feet firmly planted on the ground. That’s why we can always tell up from down. In a weightless environment, however, these signals that our bodies need for orientation are no longer there.

"We really don’t notice that we’re standing on the ceiling" says Thomas Reiter. "You first have to learn to learn to trust the information your eyes are sending your brain more than your gut feelings. The sensation of gravity simply isn’t present." That’s why all astronauts have problems with orientation the first time in orbit.

But because the human brain is so flexible, astronauts are able to slowly adjust to weightlessness over a few days. Doctors are studying this ability in the hopes that it will teach them more about medical conditions, such as the equilibrium problems experienced by many elderly patients.

Another problem is that after arriving in space, around two litres of the blood and bodily fluids that is usually distributed throughout an astronaut’s legs ends up in his abdominal cavity, chest and head. That makes a whole new set of demands on the body’s circulatory system.

Some of the symptoms that occur resemble those caused by common diseases here on Earth. When astronauts spend long periods in weightlessness, their muscles begin to atrophy and their bones become thin and brittle, especially in the spine and the legs. Unlike the similar condition common with osteoporosis, however, these degenerative conditions are halted when the astronaut returns to the surface.