Chapter 35: Disorders of the Bladder and Lower Urinary Tract

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Welcome back to The Deep Dive.

We're here to tackle those tricky pathophysiology concepts and, well, make them stick.

You asked for a deep dive into the lower urinary tract.

So today we're shifting focus downstream from the kidneys, really digging into the bladder.

Exactly.

You know, the kidney does the complex work of making urine, but the bladder, that's our essential storage tank.

Its job sounds simple, hold urine, then empty completely when told.

Sounds simple, but it's definitely not always straightforward.

Oh, absolutely not.

When things go wrong, maybe with the structure or more often the nerve control, you get these major issues, blockages, infections, incontinence, and that can actually back things right up, potentially damaging the kidneys.

So our mission today, Unpack Chapter 35, will cover the anatomy that really intricate neural wiring,

the big three problem categories, obstruction,

neurogenic issues, and incontinence, plus the key signs you need to watch for.

Yep.

Think of it like understanding a really sophisticated tank is the problem of the plumbing or is it faulty wiring?

Okay, let's start with the basic structure.

If you had to picture the bladder,

what are the, say, three key parts to keep in mind?

Right.

First, there's the main body, that's the big storage area.

Then you've got the neck, which kind of funnels down toward the urethra.

Okay.

And crucially, inside at the base, there's the trigonal.

It's the smooth triangular zone defined by where the two ureters enter and the urethra exits.

And those ureter openings,

they don't have valves.

That seems risky.

It sounds like it, but the way they enter the bladder wall means as the bladder fills and pressure rises, they get naturally compressed shut.

So that prevents urine from backing up towards the kidneys, which would be really dangerous.

Ah, clever design.

And the muscle itself needs to be both stretchy and strong, right?

That's the detrusor muscle.

It's essentially this powerful network of smooth muscle making up most of the bladder wall.

It's the muscle that does the work of emptying the muscle of the urethra.

And the lining.

Inside that is the urothelium.

It's a specialized lining, what we call transitional epithelium, the key thing.

It's basically impermeable.

It shields the body from urine's contents and can stretch incredibly thin when the bladder is full.

Okay.

So for continence, for holding it in, you mentioned a kind of dual lock system, involuntary and voluntary.

Precisely.

You've got the internal urethral sphincter first.

It's really just a continuation of that detrusor muscle down at the bladder neck.

It's involuntary smooth muscle.

But the main backup, the one we control, is the external sphincter.

That's a ring of voluntary striated muscle supported by the pelvic floor muscles.

That's our conscious hold it control.

Okay.

Now the wiring.

This always gets interesting.

Why does the body use the fight or flight system, the sympathetic nerves, just to store urine?

It seems counterintuitive.

Well, it's all about efficiency and coordination.

Storing urine is handled by the sympathetic system coming from the T11 to L2 spinal segments.

It does two things at once.

It uses beta 2 receptors to relax the detrusor muscle wall, letting the bladder fill without pressure building up.

And simultaneously, it uses alpha 1 receptors to contract the internal sphincter and the trigone area.

So wall relaxed, door locked shut.

That's storage mode.

Got it.

And then when it's time to go, the signal changes.

Completely.

The go ahead comes from the brain, specifically the pontine micturition center, and it flips the switch to the parasympathetic system originating down in S1 to S4.

And that does the opposite.

Exactly.

Emptying needs the wall to squeeze and the door to open.

So the parasympathetic nerves release acetylcholine, which hits M3 muscarinic receptors on the detrusor, making it contract powerfully.

M3, okay.

Yeah.

M2 receptors play a role too, but mostly by inhibiting those sympathetic relax signals we just talked about.

So you have these systems working in tandem, one for storage, one for emptying.

And connecting that involuntary process to finding a restroom is the somatic system, our conscious control.

Right.

That's the pudendal nerve, also from the S2S4 region, controlling that voluntary external sphincter in the pelvic floor.

It allows us to consciously override the emptying reflex.

Amazing coordination.

It really is.

The pontine micturition center in the brainstem is like the master coordinator.

It ensures the detrusor only contracts after the external sphincter relaxes.

It gets signals up from stretch receptors saying we're full and signals down from the higher brain saying, okay, safe to go now or hold on.

Understanding this detail really clarifies why so many common medications can mess with bladder function, sometimes unexpectedly.

Oh, absolutely.

Think about it.

Many common cold medicines have alpha -adrenergic agonists.

They constrict blood vessels for sure, but they also tighten that internal bladder sphincter.

Result?

Difficulty urinating, maybe retention.

Right.

And even more frequently, lots of antidepressants, antipsychotics, even some antihistamines, have anticholinergic effects.

They block that parasympathetic signal needed for emptying.

The detrusor just can't contract properly.

It can lead to significant, even dangerous urinary retention.

So if someone comes in saying they have to strain, or they're going all the time, or the stream is weak, how do we figure out what's actually happening inside?

What's the first objective measurement?

The most basic and crucial one is the post -void residual volume, the PBR.

It directly tells us how well the bladder is emptying.

How do you measure it?

Either with a quick ultrasound bladder scan right after the person voids, or sometimes with a catheter, we're looking for how much urine is left.

And what's normal versus concerning?

Ideally, you want less than 50 ml left.

That's good emptying.

If we see more than say 200 ml consistently, that's definitely inadequate emptying.

Retention is a real concern then.

Okay, but the PBR just says if there's a problem, not really why.

To get the details, like is the muscle weak or is there a blockage?

Right.

We need more advanced tests, right?

Eurodynamics.

Exactly.

Eurodynamics gives us the deeper picture.

It usually involves three key assessments, flow, pressure, and muscle activity.

Okay, walk us through them.

First is ureflometry.

Pretty simple, actually.

It just measures the speed of urine flow in ml per second while the person voids, often into a special commode that weighs the urine.

It gives a baseline of how effective the stream is.

And the second.

Systometry.

This is really the core test.

Think of it like a stress test for the bladder.

We fill the bladder slowly with sterile water or saline through a small catheter while measuring the pressure inside the bladder.

What key things does systometry tell us?

Several critical things.

It measures the bladder's true capacity, normally around 400 to 500 ml.

It tells us when the person first feels the urge to void, usually around 100 to 200 ml.

Right.

And crucially, it checks for abnormal pressure rises during filling or uninhibited contractions, signs of an overactive or poorly compliant bladder.

It confirms that, for continence, the pressure inside the urethra must stay higher than the pressure inside the bladder during filling.

High pressures during filling are a major red flag for kidney risk.

Makes sense.

And the third part looks at the voluntary control.

Yes, that's sphincter electromyography, or EMG.

We place small sensors, usually sticky patches, to record the electrical activity of those striated muscles, the external sphincter and pelvic floor.

It helps us see if those voluntary muscles are contracting and relaxing appropriately during filling and voiding.

For instance, are they relaxing when the person tries to void, or are they inappropriately contracting, fighting against the bladder?

It's often done during systometry for the full picture.

Okay, let's shift to the problems themselves.

First up,

mechanical issues, obstruction, and stasis.

So the plumbing's blocked, urine gets produced fine, but it can't get out.

Right.

And that retention is a huge risk infection.

Stones and that dreaded backflow vesicoretoral reflex damaging the kidneys.

What are the usual culprits for these blockages?

Well, congenital things exist, but mostly we're talking about acquired causes.

In men, number one is definitely an enlarged prostate, BTH.

But in both men and women, you can see urethral strictures, often from past infections or trauma,

bladder tumors blocking the outlet, and one that gets missed a lot, particularly in older folks, fecal impaction.

Really, fecal impaction.

Absolutely.

A large mass of hard stool in the rectum can physically press on the bladder neck or urethra, causing significant outflow obstruction.

It's a really important reversible cause to check for.

Wow.

Now, the chapter describes this interesting way the bladder responds, first compensating, then failing.

Tell us about the compensatory stage.

Yeah, the bladder muscle, the detrusor, it doesn't just give up.

Faced with resistance, it works harder.

It actually hypertrophies the muscle wall thickens, sometimes quite dramatically.

Like any muscle lifting weights.

Exactly.

It generates much higher pressures, maybe 50, even 100 centimeters of water pressure, trying to force urine past the blockage.

Clinically, the stage manifests as urgency and frequency.

The bladder is working over time, becoming kind of hypersensitive.

But it can't keep that up forever.

What happens in the decompensatory stage?

Eventually, the muscle fatigues, it just can't sustain that high pressure.

The contractions become weaker, less effective, and significant amounts of urine start being left behind after voiding that residual volume climbs.

And the symptoms change then?

They do.

Now, the person reports difficulty starting the stream, hesitancy, needing to push or strain, and the stream itself is weak, maybe immittent.

And the structure of the bladder wall itself starts to change too, right?

It's not smooth anymore.

No, it gets really damaged.

That smooth inner surface develops these coarse, interwoven bundles of thickened muscle called trabeculae.

It looks kind of like cords running across the bladder wall.

And that leads to pockets forming.

Precisely.

In between those trabecular ridges, the bladder lining can bulge outwards, forming little pouches called cellules.

If these get bigger, they become diverticula.

And why are diverticula such a problem?

Because they're essentially outpouchings of the lining without any muscle in their walls.

So they fill with urine, but they can't contract to empty.

They become these stagnant pools, perfect breeding grounds for infection and stones.

And all these changes lead to the classic signs of retention we see in chart 35 .1.

Distension, hesitancy, weak stream, frequency, and eventually overflow incontinence.

Alright, let's switch from the plumbing to the electrical system neurogenic bladder.

Here, the problem isn't a physical blockage, but a glitch in the nerve signals controlling the bladder.

Exactly.

It's some kind of disruption in the communication pathway.

It could be the peripheral nerves, the spinal cord, the pons in the brain stem, or even the higher cortical centers.

And it generally manifests in one of two ways.

Failure to store urine or failure to empty it.

And the key seems to be where the neurological damage occurs.

That's the fascinating part.

The location of the lesion often predicts the type of dysfunction.

If the damage is above the level of the sacral spinal cord, spinal cord injury, higher up, stroke, multiple sclerosis, brain tumors, you lose that inhibitory control from the brain.

So the lower reflexes run wild.

Pretty much.

This results in what we call spastic bladder.

It's a failure to store.

The bladder becomes hyperactive, contracting frequently and involuntarily, often with a small capacity.

And there's a dangerous complication mentioned.

Yes, especially with higher spinal cord lesions, like in the neck.

You can get detrusor sphincter dysnergia.

This is where the detrusor contracts forcefully, trying to empty, but the external sphincter also contracts at the same time, instead of relaxing.

Oh, like hitting the gas embrace simultaneously.

Exactly.

It creates incredibly high pressure inside the bladder, which is a major threat for reflex and kidney damage.

It can also trigger autonomic hyperreflexia in susceptible patients, that dangerous spike in blood pressure.

Okay.

So that's spastic bladder from lesions above the sacral cord.

What about lesions at the sacral level or in the peripheral nerves?

That causes the opposite problem.

Aflacid bladder, which is a failure to empty.

This is characterized by detrusor aflexia.

The bladder muscle loses its tone, and the person loses the sensation of fullness.

So it just stretches out?

Yes.

It becomes hugely overstretched, like a floppy bag holding large volumes of urine.

Patients often have difficulty initiating urination and may only empty by straining or have continuous dribbling that overflow incontinence picture again.

Is there a common clinical example of this?

Diabetic neuropathy is a classic one.

The person literally doesn't feel their bladder getting incredibly full, leading to chronic over -distension and eventually poor contractility.

So for both spastic and flaccid bladder, the management goals are similar.

Prevent the bladder from getting dangerously full and prevent infections.

Absolutely.

Preventing over -distension is key to protecting the kidneys.

The cornerstone of management, especially for flaccid bladder and often for spastic bladder too, is intermittent catheterization.

Usually self -catheterization.

Yes.

Patients are taught to catheterize themselves on a regular schedule, maybe every three to four hours, to keep the bladder volume down, ideally below 400 millibarers or so.

Are there other techniques?

For flaccid bladder, some patients can use maneuvers like the creday maneuver, applying manual pressure over the lower abdomen or the Valsalva maneuver straining to help push urine out.

Pharmacologically for spastic bladder, we use anti -mascarinic drugs like oxybutinin to calm down involuntary contractions.

For some milder cases of flaccid bladder, cholinergic drugs like bethanicol might be tried to stimulate contractions, but catheterization is usually more reliable.

Okay, let's talk specifically about incontinence, that involuntary loss of urine.

It's incredibly common.

The chapter breaks down into four main types based on why it's happening.

Let's start with stress incontinence.

Right.

Stress incontinence is leakage that during activities that increase pressure inside the abdomen, things like coughing, laughing, sneezing, lifting, exercising.

And what's the underlying mechanism there?

Is it a weak muscle?

It's mainly about weakened support structures.

Often due to childbirth or aging, the pelvic floor muscles weaken.

This causes the bladder, neck, and urethra to lose their normal position and support.

Specifically, they lose what's called the posterior uretervesical angle or PUV angle.

Can you explain that PUV angle concept simply?

How does losing it cause leaks?

Sure.

Think of it this way.

Normally when you cough, the pressure increase hits both the bladder and the top part of the urethra equally, kind of squishing the urethra closed and preventing leaks.

Okay.

When the pelvic floor support weakens and the bladder neck drops, that equal pressure transmission is lost.

Now when you cough, the pressure hits the bladder more than the urethra, essentially forcing the urethral door open and causing urine to leak out.

Got it.

Mechanical failure due to loss of support.

What's the second type?

Overactive bladder or OAB, also called urge incontinence.

Yeah.

OAB is defined by that sudden, intense feeling of needing to urinate right now, urgency.

It's often accompanied by frequent urination and needing to get up at night, nocturia.

The leakage happens because the person can't get to the toilet fast enough when that strong urge hits.

And what causes that overwhelming urge?

It's caused by involuntary contractions of the detrusor muscle while the bladder is filling.

It shouldn't be contracting then, but it does.

This can be neurogenic due to CNS conditions like stroke or MS that remove the brain's normal inhibition of these contractions.

Or it can be myogenic.

This means the problem is within the bladder muscle itself.

Sometimes long -term issues like bladder outlet obstruction can cause changes in smooth muscle cells, making them hyper excitable and prone to contracting spontaneously.

Okay.

Third type, overflow incontinence.

We touched on this with obstruction and flaccid bladder.

Exactly.

Overflow incontinence is leakage that happens when the bladder is extremely over -distended.

The pressure inside gets so high that it simply overcomes the urethral sphincter's ability to hold back urine, leading to dribbling or constant leakage.

So it's symptom of underlying retention.

Precisely.

The cause is either a blockage preventing emptying, like that enlarged prostate, or a bladder that can't contract effectively, like in neurogenic flaccid bladder.

And remember, again, always consider fecal impaction as a potential cause here too.

Right.

Don't forget that one.

And the last type,

functional incontinence.

Functional incontinence is different because the urinary tract itself might be working perfectly fine.

The leakage occurs because of problems outside the urinary system that prevent the person from getting to or using the toilet effectively.

Like what?

Things like severe arthritis, making it hard to walk or manage clothing.

Cognitive problems like advanced dementia, where the person doesn't recognize the need or know what to do.

Or even just poor vision, making it hard to find the bathroom, especially at night.

Makes sense.

So treatments really have to be tailored to the specific type of incontinence, targeting the underlying cause.

Absolutely.

You can't treat them all the same.

For stress incontinence, behavioral therapies are key, especially pelvic floor muscle exercises, kegels, to strengthen that support system.

For o -aburge incontinence, besides behavioral strategies like timed voiding, the mainstays are anti -muscarinic medications, Oxybutynine, Toltradine, which work by blocking those M3 receptors and calming down the unwanted detrisor contractions.

And for overflow?

Well, you have to address the underlying cause.

If it's prostatic obstruction, medications like alpha blockers, Tamsulosin, can relax the prostate muscle and improve flow.

If it's a non -contracting bladder, intermittent catheterization is often necessary.

We should also touch on bladder cancer.

The chapter notes it's the most common urinary tract cancer, much more common in men, and usually diagnosed later in life, over 55.

What's the main driver behind it?

The etiology is strongly linked to exposure to carcinogens that are concentrated and excreted in the urine, coming into direct contact with that urothelial lining.

Like what kind of carcinogens?

Historically, aromatic amines used in the dye and rubber industries were major culprits.

But today, by far the most significant risk factor is cigarette smoking.

Smokers have a much higher risk.

And the cancer type usually arises from that special lining?

Yes.

The vast majority, around 90%, are urothelial carcinomas, previously called transitional cell carcinomas, originating from that urothelium we talked about earlier.

What's the single biggest warning sign someone should be aware of?

The absolute classic sign, and the most common presenting symptom, is painless hematuria.

Blood in the urine.

Visible blood.

It can be gross, meaning visible to the naked eye, or microscopic, only picked up on a urine test.

A key point is that this bleeding can be intermittent.

It comes and goes, which unfortunately can lead people to delay seeking medical attention.

And treatment depends on how advanced it is.

Very much so.

For superficial tumors confined to the lining, treatment might be endoscopic scraping it off from inside the bladder, sometimes combined with intravysical chemotherapy, where drugs are put directly into the bladder, or immunotherapy, using the BCG vaccine instilled in the bladder.

But for more invasive cancer?

If the cancer has invaded the muscle wall, the standard treatment is often radical cystectomy, complete removal of the bladder.

In men, this usually includes the prostate and seminal vesicles too.

This obviously requires creating a new way for urine to exit the body, like an ileal loop urinary diversion.

Lastly, let's consider age extremes.

The chapter highlights older adults,

where incontinence is very common, but maybe not inevitable.

What changes contribute to this higher prevalence?

Several age -related changes can play a role.

Bladder capacity tends to decrease a bit, the urethral closing pressure might weaken, and the detrusor muscle itself might not contract quite as forcefully, sometimes leading to increased post -void residual volume.

But the crucial point seemed to be about transient causes, things that aren't permanent aging changes.

Exactly, that's a huge clinical takeaway.

A very significant portion of incontinence in older adults isn't due to irreversible bladder problems, but secondary, temporary issues that, if identified, can often be completely reversed.

And the book gives that really helpful mnemonic, right?

Diapers?

Yes, diapers is fantastic for remembering these common transient causes.

Dementia or delirium, eye infection, UTI, atrophic vaginitis or urethritis, P -pharmaceuticals, a big one, P -psychological factors like depression, E -endocrine issues like poorly controlled diabetes causing polyuria, restricted mobility,

and S -stool impaction.

Oh, that covers a lot.

It does.

And identifying and treating one of these, clearing up a UTI, adjusting a medication, treating constipation, can often resolve the incontinence entirely.

It emphasizes looking beyond just the bladder itself.

Good point.

Yeah.

And just briefly on the pediatric side, the key is that matrician starts as a simple reflex.

Right.

In infants, it's largely an involuntary spinal cord reflex.

That conscious cortical control needed for toilet training typically develops around age two to three, allowing them to learn voluntary control over the external sphincter and bladder emptying.

Hashtag tag outro.

Okay, that was a comprehensive run through.

We went from the basic anatomy through that intricate sympathetic parasympathetic control.

The dual nervous systems for storage and emptying.

Right.

Then into diagnostics like PVR and the detailed picture from your dynamic.

Yeah, measuring flow, pressure, muscle activity.

And finally, landing on the core problems.

Yeah.

It really seems to boil down to just a couple of main failure modes, doesn't it?

I think so.

When you distill it all down.

Given how many extremely common drugs, simple antihistamines, cold remedies, antidepressants, antipsychotics, Parkinson's meds have those anticholinergic or adrenergic effects we discussed.

How often might seemingly unrelated symptoms of patient mentions, maybe sudden constipation, blurred vision, dry mouth, actually be subtle, but critical clues.

Clues that perhaps they're experiencing drug -induced urinary retention, something potentially harmful, but also potentially preventable if we connect those dots.

That's a really important point about looking at the whole patient and the side effects of something definitely worth keeping in mind.

Thank you for joining us on this deep dive today.

We appreciate you listening.

We'll catch you next time.