Microgravity seems to reshape astronaut anatomy into spheres

Astronauts conduct a lot of scientific experiments in space, sometimes becoming part of those experiments themselves. While the Kelly twins stood out as a big opportunity to study the effects of living in space on the human body, other astronauts routinely gather data on their own bodies, measuring their eyes, hearts and other physiology for signs of change or trouble. Finding these changes hasn’t been hard, as microgravity seems to be rather disruptive to living systems that have had millions of years to get used to the constant pull of the Earth. Sometimes these changes are temporary and cosmetic, such as fluid buildup in people’s cheeks giving them puffier faces, but others found in heart and brain might be a bit more serious.

Relaxed and rounded hearts

Human hearts aren’t heart-shaped, but they’re normally not round either. The slightly oblong muscle, like the rest of the body, has evolved to function with a bit of resistance and also assistance from gravity. After spending time in space, ultrasounds revealed that astronauts’ hearts were becoming more spherical. This is because of how fluids end up getting redistributed in the body, plus because the heart just doesn’t have to work as hard when everything is floating. Giving the heart a rest isn’t great if you’re planning to return home to Earth though, as the reduced effort seems to lead to a loss of muscle mass, leaving a weaker heart to work even harder under normal gravity.

The good news is that this rounded, more relaxed heart isn’t a shock to scientists, who actually predicted this risk before observing it in astronauts. This means that their models for how gravity affects the heart are correct, and that they should therefore be in a good position to help develop exercises and treatments to help astronauts avoid more dangerous scenarios when humans start spending more time in space.

Balled-up brains

Astronaut brains have been found to show some similar reshaping, but for slightly different reasons. Without stronger gravity to pull cerebrospinal fluids down out of the skull on a regular basis, it seems that a build up of fluid may be shifting brains positioning, or even compressing them slightly in unusually full heads. There were also increases in the amount of gray matter in certain regions of astronauts’ brains, specifically around areas that process and control the legs.

At this point, the hypothesis is that people in microgravity are needing basically having to relearn to move with their legs in an environment where you can’t walk. Rather than discrete training times, astronauts’ brains are working on what their legs can do all day long, meaning they’re in a constant state of a flux and attention. There’s no immediate concern for astronauts’ ability to walk at this point, but there is a chance that this rewiring will never be completely undone. Even after returning to Earth, their brains may handle walking slightly differently for the rest of their lives, even if the end result is still a stroll down the street.

All of these changes are of course being monitored not just for the sake of our current astronauts, but also for future generations as well. With the chance for humans to travel to another planet inching ever closer, we need to figure out ways to ensure future explorers’ bodies are ready to cope with the trip.

Source: Astronauts' brains change shape during spaceflight, Science Daily