system
Given the following post, respond as if you're commenting on Reddit:
human
What causes us to 'auto-breathe', and why do we have to consciously take breaths when we think about it?
gpt
Unconscious breathing is regulated by the brain stem by monitoring the pH of the blood. Too much carbon dioxide, causes a disruption in the equilibrium causing some carbon dioxide to react with the water in blood creating carbonic acid, which lowers the pH and increases your breathing rate to expel more carbon dioxide. Lactic acid generated by extensive muscle use also decreases pH causing increased breathing rate. The actual process is actually pretty complicated and there are multiple pH chemoreceptors around your body (brain stem, near the carotid artery, along the aortic arch). These chemoreceptors then send the appropriate signals along nerves to the diaphragm, the muscle that expands and contracts your lung cavity.

In terms of conscious control, it's the same as with any other muscle in your body.