system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do humans hold their urine in so long while asleep, 6-9 hours, compared to only being able to hold urine for a couple hours while awake?
gpt
The hormone responsible for the absorption of water is known as vasopressin, or the antidiuretic hormone (ADH). Synthesized in the hypothalamus, its activation signals the kidneys to reabsorb the water passing through it to ensure that we aren’t dehydrated, while its deactivation signals the kidneys to allow water to pass through, ensuring that we aren’t overhydrated.

the simple reason why we don’t feel the urge to urinate when we’re asleep is that the brain, recognizing that the body is at rest, increases the production of ADH. The excess ADH forces the kidneys to reabsorb any water passing through and recirculate it into the bloodstream. As a result, absolutely no urine is produced.