The Need To Pee

When ya gotta go ya gotta go. Or do you?

In the late 16th century, Tycho Brahe was one of the most renowned astronomers in Europe, celebrated for his meticulous observations of the stars and planets. His fame brought him into the company of royalty and nobility, who often sought his presence at various banquets and courtly gatherings.

On one such occasion in 1601, Brahe was invited to a lavish dinner hosted by a nobleman in Prague. The banquet was, by all reports, as sumptuous as you might think, with tables laden with the finest foods and wines, and the most esteemed notables of the region in attendance. Tycho, ever the dignified guest, was seated among them. As the hours wore on, he began to feel an increasingly urgent need to relieve himself.

In that era, and especially in such refined company, it was considered improper to excuse oneself from the table before the meal had concluded. Tycho, not wishing to offend his host, decided to endure the discomfort. 

Eventually, the banquet came to a close, and Tycho, in considerable pain by this point, finally made his way home. But by then, it was too late. Despite the best efforts of his physicians to see to his ailing kidneys, Tycho's health rapidly declined. On October 24, 1601, Tycho Brahe passed away. The cause of his death was likely a bladder or kidney infection, exacerbated by the pressure and strain of that fateful evening.¹

The world’s most famous urination. Photo by Andre Morales Kalamar on Unsplash

Taking out the Trash

As the body’s cells carry out their normal everyday duties, their activities produce substances which are not useful or, worse, toxic. On this list are products such as creatinine and uric acid, an especially vexing product to those of us afflicted with gout. Similarly, digesting food leads to unusable and, again, potentially toxic bits, including ammonia. And then sometimes we poison ourselves with various chemicals that have some pleasant effects—whisky is my personal poison—but  must eventually be removed from the body.

The first phase of the process to eliminate these harmful substances occurs in the kidneys. Nephrons are specialized structures whose function is to filter. Nephrons separate the good stuff from the bad stuff. This bad stuff is then combined with water to produce what would be Brahe’s undoing, urine.

This liquid, with lots of stuff that needs to be gotten out of the body, is stored in a muscular sac, commonly known as the bladder. We use the word “the” to refer to it, but a bladder, generally, is really just a bag to store stuff in that uses compression to get whatever is in the bladder out. Some fish have swim bladders that hold gas that can be inflated or deflated to control buoyancy.

Like most creatures, humans don’t go around just emptying their bladders willy-nilly; we don’t bother emptying it until a reasonable amount of fluid has accumulated. While there are of course individual differences, your average bladder can hold between 300 and 500 milliliters. As you might have guessed from the Brahe case, the process to encourage emptying it kicks in well before it’s full.

Muscle Measurement

For this measurement, unlike some of the others I have discussed, it’s possible to understand what’s going on all the way down to the cellular level.

Embedded inside the bladder wall are specialized cells called “mechanoreceptors.” As the bladder fills with fluid, the walls stretch, just like the rubber does when you blow air into a balloon. As the walls stretch, the cell membrane of the mechanoreceptor is deformed, allowing ions (sodium and calcium) into the cell. For those of you who remember your introductory psychology class, you know that these charged ions generate an action potential—a signal—to the cell or cells down the line. And, voila, the increasing volume of liquid causes stretching, creating  an action potential. In this case, the signal goes from the bladder to the spinal cord and on up to the brain.

A properly functioning bladder and nervous system will produce this signal as the bladder starts to get full. It should be clear that because of the way these mechanoreceptors work, they are measuring how much fluid is in the bladder because the stretch of the wall is reliably correlated with the amount of fluid, in the same way that a balloon’s sides get increasingly stretched out as you add more and more air.

A similar principle is at work when it comes to the stomach. One of the cues that gives rise to the feeling of satiety, the opposite of hunger, is how much is in the stomach. As the walls expand, hunger decreases and satiety increases. This is why bariatric surgery works: with a smaller stomach, patients feel less hungry after eating a smaller amount of food.

Motivation

So, that’s more or less how fluid enters the bladder and accumulates. How does it get out? As you go about your day, there is a little muscle ring² that is, by default, kept nice and tight. This muscle, sitting astride the tube that goes from your bladder to the outside world, prevents liquid from escaping, just like pinching the neck of a balloon when you pause to take a breath.

And, just like a balloon, if you loosen the ring, the stuff inside is squeezed to the outside. If you don’t loosen the ring even when the bladder gets fuller and fuller, bad things can happen, just as adding more air to a balloon will eventually cause it to pop. As the volume of liquid increases, the signal that starts all the way back with the mechanoreceptors motivates you to relax that little muscle ring, letting some air out of the balloon, in our analogy. That feeling of a full bladder motivates you to pee, getting rid of the fluids that contain waste products and toxins.

Now, a consequence of the fact that under normal conditions the little muscle tube is kept tight is that there are a number of situations in which matters loosen up, even without instructions from the brain.

Perhaps most straightforwardly—but not in Brahe’s case—a very full bladder can lead to involuntary excretion. Research suggests that as the muscles of the bladder expand further and further, the spinal cord takes the decision, as it were, to loosen up the muscle loop. The fact that Brahe was able to suppress this reflex illustrates that there can be conflict between what one wills, voluntarily, and the action of other parts of the nervous system. In this case, Brahe³ “won” that battle but, well, lost the war.  

Also straightforwardly, death causes the relaxation of muscles, which in turn leads to involuntary urination.

A number of other stimuli can have this effect. It is true, as is sometimes portrayed in films, that overwhelming fear or anxiety can do so. As a general matter, great psychological stress can activate or deactivate muscles that under normal circumstances would be under voluntary control.

The Costs and Benefits of Voluntary Control

DALL-E renders the night in question.

Brahe’s story raises a question about voluntary control. In this case, it seems like the fact that we can, with sufficient willpower, suppress a motivational signal being generated by the body is something of a Bad Thing. Why are we able to fight our evolved motives, even to the point of causing death?

This question is, to my mind, a deep one, and I won’t pretend to answer it definitively here.

Life is, in a word, complicated. At any given moment, the costs and benefits of urinating depend on a wide array of factors. For us humans, many of those factors are social: there are society rules and norms that produce costs if one urinates in a time or place that is moralized.

Most of the time, then, feeling the motivation but being able to decide whether or not to act on it is a very Good Thing. By being able to weigh many different competing motivations—excreting waste versus violating a norm—we can make better decisions.

This flexibility is often very important. As you exercise, the motivation to stop doing so rises. Everyone—especially those of us who do CrossFit—is familiar with this sensation. It is, to be sure, to our benefit that we can choose to continue even when our muscles are asking us to stop. Because of this, we can give our muscles the sort of challenge they need to grow and, if we are being chased by a bear, we can continue to run despite the discomfort.

In the case of eliminating wastes, there are probably any number of occasions when one feels the need to pee, but other matters take precedence. One might be in one’s residence, which is best kept free of toxins and so forth. One might be trying to avoid being tracked, in which case waiting until the danger has passed might be a good idea.

Humans have a tremendous array of motives because we’re so complicated. In particular, we are deeply social creatures and our choices can have important effects on how others view us. Therefore, it might not be surprising that we have so many different conscious experiences and so many actions under our voluntary control. As the number of motives expands, the greater the need to weigh the urgency of one motive over another.

And that, my friends, is why consciousness evolved.

That is, how does the brain figure out, exactly, which is more important, conforming to a norm or peeing? Is there a common mental currency that allows the brain to say it’s this important to be polite but that important to pee, and right now this is bigger than that? Does every sensation have to be converted to some common mental currency so that good decisions can be made? Is the strength of our feelings that common currency?

Great questions.⁴

POSTSCRIPT

As promised, here are the results of the polls regarding household conflicts. According to the eye-test, people are actually fairly good at predicting how much conflict with partners is about living space. Huh.

1. A similar tragedy occurred in 2007. Jennifer Strange died competing in a contest called “Hold Your Wee for a Wii” in which participants competed to drink the most water without urinating. Her family would subsequently win a law suit over the incident. 

2. This is called the urethral sphincter, which I feel like is the sort of phrase that belongs down here, in a footnote.

3. I recognize that this is an odd phrasing. Cases such as this one illustrate the value of the modular view of the mind. Intuitively, we identify the “person” with the modules that are associated with voluntary action. The modules that motivate peeing are just as much Brahe as the modules that were working in the opposite direction. I wrestle with this in Hypocrite and in this paper.

4. See, for example, work by Bernard Baars—Global Workspace Theory—and the late Daniel Dennett—especially Consciousness Explained.