I have always assumed that there is a pressure stimulus that asserts itself when the urinary bladder becomes distended from being full of piss. But I have also noticed that another type of stimulus is received when a small amount of urine in the bladder is in a concentrated solution, ie the urine is really dark yellow.
Is there a primary (pressure) and a secondary (concentration) stimulus from the bladder that tells us when to urinate?
Is this a stupid question or is there just no answer? Anyway, bttt for another try.
I am not aware of a concentration stimulus within the bladder. Your personal experience with this phenomenon may not be applicable to the population as a whole.
WAG: It may be that the Squeeze response is what the bladder does, and it is triggered by pretty much any stimulus there.
As the sneeze response is triggered by the nose sensing cold, by tickling, by the sun shining on the surface of the nose, etc.
And tears are triggered by multiple different emotions, physical prodding, heat, cold, etc.
I don’t have an answer, but I have experienced the phenomenon the OP’s referring to, so while it might not be applicable to the population as a whole, he’s not completely alone.
The photic sneeze reflex is triggered by the sun shining on your pupils, actually.
I suffer garage stimulus. This is no joke, I will have no urge to urinate and as soon as I go in to my garage (for any reason) I have an overwhelming urge to urinate. Anyone care to tackle that one?
Jim Mac Millan
I am not a doctor. I am not a biologist.
This website did not mention your issue, but did say, “When the bladder has filled with urine, stretch receptors in the bladder walls send messages to the reflex voiding centre.” Ho hum.
You can read about the, Autonomous Bladder Hypothesis here. “When, alpha beta -MATP (30-3000 nmol/L) or substance P (30-300 nmol/L) was added to resting bladders there were small rises in intravesical pressure (<2 cmH2O).”
It sounds like you’ve somehow been conditioned that way – I can’t go into a bathroom, even to brush my hair, without having to stop and pee. But that makes more sense than the garage…still, the human body is a wondrous and weird thing.
Many people (including me) sometimes have the urge upon entering their home and sometimes any building. The “garage syndrome” appears to be a similar reaction. I don’t know the physiology behind this, however. The cite above stated:
However, it later states that the stimulus is received when the bladder contains 175 ml or so of urine, which is far from being full. The bladder is elastic, and when I was unable to avoid recently due to an enlarge prostate, the ER catheterized 1400 ml. Quite a stretch.
But I don’t know the answer to your question either.
IANAD, but my WAG would be that irritation of the bladder walls from the composition of your urine might cause you to get the urge to pee.
Just wondering if this is always true, or just in the morning? While we often pee upon first waking up, I have found this urge sometimes is delayed. It could just be coincidence when you feel you have to pee a little later, in the garage.
Could this be true in your case?
The stretch-urge curve is not linear. When the bladder is filled to a certain volume (175ml apparently) it will stimulate the stretch receptors. The initial urge is not very strong, and can be ignored if it is not convenient to go to the restroom. Subsequent filling produces stronger and more frequent urges that can still be ignored to a certain degree until the urge is so strong you have to put your beer down and wait in line at the restroom.
Interestingly enough, and you may have experienced some of this barbitu8, the bladder loses its contracability if the muscle is stretched too far. So it is possible to hold it to the point that you can’t urinate. That’s when you get catheterized at the ER.
I have never personally been catheterized, but patients complain that it gives them the constant sensation of having a full bladder. The balloon on the end of the tube (that keeps it from coming out) is only 10-20mL. This supports the theory of irritation causing the sensation.
USCDiver, soon to be doctor
How come, when the bladder is full and you’re dying to go, you will hit a brief plateau when the urge subsides for a brief moment…buying you just a little time. It almost seems as if the urge comes in waves (or irregular intervals). Anyway, do the bladder muscles go through periodic contractions (or spasms) giving the feeling of urgency that comes, relaxes, and returns? Does the urgency come from
the receptors alone? - Jinx
I got instant and great relief from the catheterization at the ER. I was in real agony. I also was catheterized while I was hospitalized a few days prior (which, incidentally, caused the problem with my prostate - it appears that an operation can aggrandize the situation), with a Foley for a couple of days. No sensation of having a full bladder. However, due to the great distension of the bladder, the bladder had lost tone and I was unable to void even after laser surgery for the prostate. It took a few days for the bladder to regain enough tone to contract. (And due to the Foley being in there for about three weeks, I had great irritation of the penis, which is also no fun; compound that with avulsion of my right Achilles’ tendon, those were not the happiest days of my life.)
I really don’t think so. It can be anytime. I see your point about delayed reaction though. I think there is something to be said of another post. When I was a child my parents had a garage full of all kinds of junk. It contained things that most kids would have found fascinating. In hindsight I remember staying out there until I had to go to the bathroom so bad I would have to run to the house. I think I may have found my connection.
Jim
:rolleyes: This should be obvious. It’s because every time you went on a family trip as a kid, you’d all go out to the car and your dad would say: “It’s a long drive, if you gotta pee, go now! I ain’t stoppin’ half-way there!” 
I’ve noticed two relationships regarding bladder contents:
The urge to void (and the difficulty holding it in) is inversely proportional to your distance from the intended receptacle. Thus, if you have been holding it in during your commute home, and your front door is locked, and then your only bathroom is occupied by your teenage daughter, then you are most likely to soil your clothes outside the bathroom door regardless of how long your commute home is. (This relationship also applies to the bowels.)
Beer-induced urine stimulates the need-to-piss response much more strongly after the first bladderful has been voided. You can drink six pints before your first trip to the bathroom, but after that first trip, every glass of beer prompts another trip to the pisser.