system
Given the following post, respond as if you're commenting on Reddit:
human
Why do animals (including us humans) have symmetrical exteriors but asymmetrical innards?
gpt
Most of our asymmetry is due to just two organ systems: the GI tract and the heart. The concept that best explains the shape of both of these systems is the idea that a long organ that has to fit in a small body does so by being wound up.

The heart could be composed of a linear arrangement of a pump, the lungs, and then a second pump. In some organisms like the worm, the heart is a linear pump. However the human body cannot accommodate a linear arrangement and thus we have what is effectively a tube curled up on itself.

The GI tract is the same story. It would be hugely long if a linear, thus it has to be wound up inside of us. There is no symmetrical way to wind it up. Many organs like the pancreas and the liver actually bud off of the GI tract during development so the asymmetry of the GI tract explains the asymmetry of many of the other abdominal organs. However those organs not involved in the GI system like the ovaries in the kidneys tend to be relatively, although not perfectly, symmetrical. Likewise the lungs are not perfectly symmetrical because the left lung must accommodate the heart.

The one interesting thing about this whole conversation is that the direction that things rotate in the human body during development is due to tiny molecular motors called "cilia". If there is a genetic defect in just a single protein that composes the cilia, the cilia are no longer able to guide the process and there is a 50/50 chance that the organs will rotate the "wrong" way. This leads to the inversion of all symmetry in the human body called "situs inversus". This leads to occasional moments of extreme confusion for doctors, seeing as patients often don't even know they have reversed symmetry.