Question: If you stand on you head in space, does the blood trail downwards towards your head?

Jonathan Scott answered on 7 Oct 2015:

Hi Georgie-May

Great question. No it doesn’t. When you stand on your head on Earth, blood and fluids move towards your head because of the effects of gravity – when you stand up normally blood and fluid move towards your feet for the same reason, but your body has several very clever systems for ensuring that this doesn’t happen too much and that some blood and fluid remains in the upper half of your body (and your brain).

In space, you don’t experience the effects of gravity, so you don’t have any body weight and the blood and fluid also weigh nothing. So, no matter how you position yourself, the blood and fluid isn’t ‘pulled’ in any direction.

However – and this is a big however – because you do not experience the effects of gravity in space, the larger amount of fluid that is normally in the lower half of your body moves slightly towards your upper half – it distributes itself more evenly thoughout your body. This is called a ‘fluid shift’ and you can actually see it in the faces of astronauts – their faces become ‘puffy’ and sometimes they can look quite different to how they do on Earth. This fluid shift may also have some other effects on the body, because it increases the pressure inside your head – we still have lots to learn about this.