You know what I mean. Normally most of the time if you have “the urge” you can hold it a really long time pretty much without any conscious effort. However if you hold it long enough eventually you’ll get to a point where you simply cannot contain it anymore: it’s urgent and you’ve got about 90 seconds to get to a restroom, a bush, a fire hydrant, or whatever your preferred waste receptacle may be because it’s going to come out no matter what.
What is the mechanism behind this? Is it because your body is trying to put more liquid into your bladder so room must be made, or is it just your brain sending an urgent “evacuate” order, i.e. is it primarily physical, psychological, or both?
Essentially. The kidneys never stop producing urine and feeding it into the bladder, and your bladder can only stretch so far before something has to give. When that happens, urine leaves through the path of least resistance which is normally the urethra. Think of a water balloon with two necks on it. You’re pinching one neck shut while someone with a hose fills it from the other neck. Fairly soon there’s a point where the balloon feels full and tight but the pressure isn’t really bad–you could keep filling it for a while. But eventually there comes a point where no matter how tightly you pinch the neck of that balloon, the water is just too pressurized for you to hold it back any longer, and out it comes. Your bladder has stretch receptors in it that send signals to your brain telling you how close you are to that point.
But keep in mind that that point is flexible. Stretch receptors send signal, saying we’d like to void. Brain/circumstances override it due to no bathroom nearby, involved in movie that can’t be paused, etc. Receptors back off, tolerate it a bit longer. Get stretched further, hit a new stretchpoint, re-send signal.
Also proximity to a commode can also trigger the urge. Urgency not so great, get closer and closer to urinal/toilet, the urge becomes almost overwhelming the closer you get. Often, patient ends up starting to pee just before they get there.
Urinary retention can also be a problem. Get stretched too far, the bladder muscle becomes too atonic to squeeze the urine out real quick. And if you’re a guy with a big prostate, suddenly emptying your bladder becomes a huge difficulty.
Which begs the question: WHY does that urge become so, well, URGENT just by walking toward the toilet? It’s annoying as hell. I mean, you need to go but you don’t NEEEEEEEED to go, so you head to the bathroom and start fumbling with clothing, and the bladder’s proximity sensor goes WHEEEEP WHEEEEP WHEEEEP and you’re doing the pee-dance trying to hold it in long enough to sit down on the damn toilet! (us girl-types, that is, I can’t speak for those with “outdoor plumbing”, so to speak).
As I recall, this has been discussed elsewhere on the board and it’s because there are actually two sets of reflexes and muscles involved. One set is the voluntary set that you consciously decide to release. The other is not consciously controlled; it is what keeps you from messing yourself when you aren’t paying attention or are asleep, but when it “thinks” it is time to go it releases and suddenly your voluntary muscles are doing all the work. Therefore it suddenly feels much harder to hold in, because it is.
Related to this, why is it that sometimes when you’re “desperate”, when you do let fly it’s clear that your bladder wasn’t actually that full at all, as you only pee a small amount, whereas other times you can be not that desperate and produce a pint or more? What’s that all about?