system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a -- and if so, what is the -- "feedback" mechanism from the bladder to the kidneys? (Is there a message like, "Stop already!!"?)

Like normal humans, I wake up in the morning, put on my glasses, and take a humongous morning pee.  It has not been an emergency to get to the bathroom; I am not in pain; etc.

Thing is, I can void nearly the same volume an hour later.

It's almost like, say, at 3ayem the bladder told the kidneys to take a break for a few hours, then later called them back to work to "finish the job" -- which results in the large volume of the second trip.

Is there a special nerve for handling this situation?  Some special fast-acting enzyme that makes it back to the kidneys via the bloodstream?  What?
gpt
No. The kidneys keep making urine regardless of what state the bladder is in. This is necessary because our bodies make waste continuously, so we need to make urine continuously. If there is a distal obstruction impairing urine flow (large prostate, big stones, neurologic injury, etc), the urinary tract dilates and can ultimately rupture. At a cellular level the kidneys do eventually become unable to filter as much urine due to back-pressure, but that's not something the body was actually trying to do, and is Very Bad. This can lead to temporary or permanent kidney failure. Relevant search terms here include obstructive acute kidney injury, hydroureter, hydronephrosis, calyceal rupture, and pelvic urinoma.

The reason you pee a lot in the morning is probably more due to your brain suppressing the urge to urinate overnight, possibly with a contribution from gravity. Standing up can certainly change the distending pressure on the nerves innervating the bladder and generate an urge to urinate.