Suppose a person, drank 400ml-800ml of water, and he pees after 6 hours, when he wakes after sleep in the night. Keeping that context I'm concerned, if this could cause kidneys to damage (or fail!).
On searching multiple reliable sources (via Google), conclusion is:
holding your pee can cause your bladder wall to strech and can damage, and may increase risks for kidney disease.
But I'm doubting, that does this just increases risk, or does actually does damage to kidneys?
My career choice (primarily Emergency Medicine) guaranteed that it would be necessary to postpone micturition on a regular basis. A nights-only colleague in our very busy ED would succinctly sum up how busy the night was: a) "Not a wink" (too busy to grab any sleep), b) "Not a bite" (too busy to stop to eat), or c) "Not a pee" (so busy there was no time for a bathroom break.) Since I mostly worked days, which are busier than nights, I often had 12 hour "type c" shifts.
Does one's bladder accommodate? Yes, it does.
The normal adult bladder response to filling at a physiologic rate is an almost imperceptible change in intravesical pressure. During at least the initial stages of bladder filling, after unfolding of the bladder wall from its collapsed state, this very high compliance (Δ volume/Δ pressure) of the bladder primarily results from its elastic and viscoelastic properties. Elasticity allows the constituents of the bladder wall to stretch to a certain degree without any increase in tension. Viscoelasticity allows stretch to induce a rise in tension, followed by a decay (i.e., stress relaxation) when the filling (i.e., stretch stimulus) slows or stops. ...The urothelium also expands but must preserve its barrier function while doing so. ...In the usual clinical setting, filling cystometry seems to show a slight increase in intravesical pressure, but Klevmark elegantly showed that this pressure rise is a function of the fact that cystometric filling is carried out at a greater than physiologic rate and, at physiologic filling rates, there is essentially no rise in bladder pressure until bladder capacity is reached.
"Physiological" means, basically, normal human activity, including heavy fluid consumption. "Filling cystometry" is not "normal/physiological": it's a bladder with a catheter that is filled by forcing fluid into the bladder trough the catheter at a much faster rate than the kidney can produce urine. (It's unpleasant.)
In plain English, the empty bladder is wrinkled and folded upon itself somewhat like a raisin. Think of raisin -> grape. There is basically no change in pressure (which would result in backing up into the ureters/kidney) from fully empty to fully full. At that point, you couldn't hold it in anymore; you'd "leak".
Suppose a person, drank 400ml-800ml of water, and he pees after 6 hours, when he wakes after sleep in the night. ...could (this) cause kidneys to damage (or fail!)
No. If your bladder is small (some people do have smaller bladders than others), you will awaken with an urge to go long before urine backs up into the ureters to the kidney (urine backing up is not normal. It indicates pathology of some kind.) 400 cc is only 13 oz, or a bit more than 1.5 cups. During sleep, the pituitary gland secretes Antidiuretic Hormone (ADH) which decreases the production of urine, one of the adaptions that lets us get a full night's sleep. You probably wouldn't wake up for that. 800 cc, on the other hand, is a (relative) lot of water. You might wake up during the night with the urge to go. I probably would not.
Have you ever noticed that even if you urinate on getting up, you still need to urinate a relatively short time (1-2 hrs) later? That's partly because ADH secretion is turned off.)
Some of what that article stated is true, but not much, and not for the correct reasons. Beware of believing what "sounds true enough" on the internet. Reliable sources will have citations to reputable literature. While this article does have citations (click on 5 Sources), the author has misinterpreted and cherry-picked bits. That's why people with advanced Biology degrees must learn how to evaluate the literature. MDs are even tested on their ability to best interpret papers. PhDs learn by doing it day in and day out. Ask me how I know.
If holding urine back caused kidney damage, I'd be on dialysis and the kidney transplant list right now!
