Question

why does not the high atmospheric pressure at sea level squash us

Answer 1

it is because our body has adapted to stand up to the pressure by using flow of blood

Answer 2

This is due to the presence of the chest cavity within our bodies which keep the pressure outside and inside the same. And this is regulated by breathing.

For eg. If the pressure outside is higher than inside, we breathe in, thereby leveling the pressure (as air moves from high pressure to low pressure). And when it's higher within our bodies, we breathe out.

That's not the complete description of the mechanism of breathing, just thought it would be cool for you to know. This is how I understand it, feel free to correct me if I' wrong, and rate me if I'm right. Cheers!