Astronauts are taller in space! On Earth, gravity compresses our spine. When gravity is weak, the space between the vertebrae in our spine is able to expand.

In space, muscles aren't really needed to hold up the body. Over time, they become weaker and deteriorate (worse). Astronauts must exercise everyday to prevent this from happening.

Blood is normally pulled towards our feet by gravity. But in space, the blood and fluid is pulled towards the head giving astronauts puffy faces.

Like our muscles, bones aren't needed much in microgravity. Without exercise, they deteriorate and become weak and brittle.

In space, hearts don't have to work as hard to pump blood around the body. So eventually, they may shrink, which can cause problems for astronauts when they return to earth.

Cosmic radiation, stress, insomnia and trying to re-orient your body's balance system mean the astronaut's brain is constantly adopting while in space.