Chapter 35: Disorders of the Bladder and Lower Urinary Tract

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Welcome to the Deep Dive, where we really try to give you the fastest, most effective way to get a grip on complex source material.

And today, yeah, we're cracking open chapter 35 of Essentials of Pathophysiology.

It's all about the lower urinary tract.

Exactly.

So our mission today is to, well, map out how the bladder works, you know, storing urine versus getting rid of it.

And then we'll chart the big problems, obstruction,

nerve issues, incontinence,

and cancer.

We're basically building you a quick mental map of this whole area.

It sounds simple, but it's actually really delicate balance.

The bladder's core job is storage, yes, but also controlled expulsion.

Controlled being the key word there.

Absolutely.

Because if that control fails, urine backs up.

That's called viscarrital reflux.

And well, that can lead straight to kidney damage.

It's serious stuff.

Okay.

So to get the problems, we need the basics of control.

You mentioned it's like a ballet.

Sort of, yeah.

You've got the main muscle for pushing urine out the detrusor that's involuntary.

And then you have two gatekeepers, the sphincters, one internal, also involuntary, and one external, which is the one you control voluntarily.

Got it.

So it's this mix of the autonomic nervous system doing its thing automatically, and the somatic nervous system giving us conscious control.

That's how we stay continent.

Precisely.

Right.

Let's visualize the bladder itself.

What are the key parts?

Okay.

Structurally, think of it in two main sections, the body, which is the main storage pouch, you could say, and the neck, which funnels down into the urethra, the two bleeding out.

And inside, is it just a smooth bag?

Mostly, but there's a key landmark,

the trichome.

It's a smooth triangular area at the base.

Imagine the two ureters,

tubes in the kidneys, plugging in the top corners,

and the urethra opening the bottom point.

Okay.

But the real workhorse muscle wrapping around almost everything is the detrusor.

It's job,

contract, and empty.

Simple as that, function -wise.

But the control isn't simple.

You mentioned three neural centers, starting with the spinal cord.

Right.

The spinal cord is where the basic reflexes live.

And it's neatly divided, one set of nerves for storage, another for emptying.

Okay.

Let's break that down.

Which nerves do what?

So for storage, think S, for storage, that's the sympathetic nervous system.

The signals travel down the hypogastric nerve, roughly from the T11 to L2 spinal segments.

And what do those signals do?

They tell the detrusor muscle to relax, allowing the bladder to fill, and they tell the internal sphincter to contract, to keep the gate closed.

Make sense.

And for emptying?

Emptying, or peeing P, for pushing peeing, that's the parasympathetic system.

Via the pelvic nerve, originating down in S1 to S4, these signals do the opposite, contract the detrusor muscle strongly.

Okay.

So sympathetic stores, parasympathetic pushes, but what about holding it when you need to?

Ah, that's the final layer, the voluntary control.

That comes from the somatic nervous system, specifically the pudendal nerve, from S2 to S4.

It lets you consciously tighten that external sphincter.

Got it.

So that's level one.

What's the next control center?

Level two is up in the brainstem,

the pontine -micturition center.

Think of this as the coordinator, the conductor of the orchestra.

What's it coordinating exactly?

It makes sure that when the parasympathetic system says, contract the detrusor, the somatic system simultaneously says,

relax the external sphincter.

They have to work together seamlessly.

And if that coordination breaks down, you mentioned spinal cord injuries.

Yeah.

That's where you get a really dangerous condition called detrusor sphincter dysanergia.

The bladder is squeezing hard, but the exit door, the external sphincter, is claimed shut.

Wait, that sounds bad.

Like internal conflict?

What's the immediate danger there?

High pressure.

Extremely high pressure.

It's like squeezing a balloon with the nozzle tied shut.

That pressure can blast urine right back up the ureters into the kidneys.

That's the reflux we talked about.

It causes hydronephrosis kidney swelling and can lead to really severe rapid kidney damage.

It's basically a functional blockage.

Okay, so spinal cord pons.

What's the third center?

The highest level.

Ah, the cortical centers up in the brain.

These give us conscious awareness and the ability to inhibit the pontine center, basically the power to say not now and delay urination until it's appropriate.

Right, the social override.

Exactly.

And knowing this wiring leads us right into how drugs work.

Say you have an overactive bladder.

The detrusor is contracting way too often.

How do you stop that?

You'd want to block the signal telling it to contract, right?

So block the parasympathetic input.

Precisely.

Specifically, clinicians target the M3 muscarinic receptor subtype on the detrusor muscle.

That's the key receptor for triggering contraction.

So anticholinergic drugs are commonly used.

They block those M3 receptors, making the detrusor less likely to contract spontaneously or too strongly.

All right, we understand the normal function and control.

How do we actually measure if things are working correctly beyond just a physical exam?

Well, one of the most basic yet crucial measurements is the post -void residual, or PVR.

How much urine is left in the bladder right after someone tries to empty it.

Okay, and what are the key numbers there?

It tells you a lot about emptying efficiency.

Generally, less than 50 milliliters left is considered good, adequate emptying.

But if someone consistently has more than 200 milliliters left, that's a clear sign of inadequate emptying, and you definitely need to investigate why.

Okay, 50 good, 200 bad.

Got it.

What if you need more detail?

You mentioned urodynamic studies.

Right.

These are the more in -depth tests.

There are three main ones we look at in this chapter.

First is uroflometry.

Flometry.

Measuring flow.

Exactly.

It measures the rate of urine flow during urination.

How fast can the bladder push it out?

It helps assess if there's an obstruction or if the detrusor isn't contracting strongly enough.

Okay, what's next?

Second is systometry.

This one is all about pressure and capacity.

We slowly fill the bladder with sterile water, or saline, and measure the pressure inside as it fills, and also during voiding.

What does that tell you?

A lot, actually.

It can detect those unwanted, uninhibited contractions seen in overactive bladder.

It measures the bladder's total capacity,

and it identifies the point where the person first feels the urge to void normally around 150 to 250 milliliters, and when they feel truly full.

I see.

And the third one?

Third is sphincter electromyography, or EMG.

This looks specifically at the electrical activity of those voluntary muscles, the external sphincter, and the pelvic floor muscles.

Ah, checking if the voluntary part is working with the involuntary part.

Exactly.

It tells us if those muscles are contracting and relaxing appropriately, and crucially, if they're coordinating properly with a detrusor muscle during filling and emptying.

It's key for diagnosing things like that detrusor sphincter dyssynergia we talked about.

Okay, let's move into the problems, the pathophysiology,

starting with lower urinary tract obstruction.

So, the kidneys are making urine fine, but it can't get out properly.

Right, it's retained.

And the causes are usually mechanical blockages, super common.

In men, the number one cause, by far, is an enlarged prostate gland, benign prostatic hyperplasia, or BPH.

Okay.

In both men and women, you can get urethral strictures, which are narrowings of the urethra, often due to scarring from past infections or trauma.

So, when there's a blockage, the bladder doesn't just give up, does it?

No, it tries hard to compensate.

There's an initial compensatory stage.

The detrusor muscle actually gets thicker, it hypertrophies, to generate more force to push past the obstruction.

What does that feel like for the patient?

Clinically, that hypertrophy often leads to urinary frequency and urgency because the thicker muscle can be more sensitive and irritable.

And what's happening inside the bladder during this stage?

If you could look inside, the normally smooth lining starts to look different.

The muscle bundles become more visible, forming coarse ridges called trabeculae.

Trabeculae.

And between these ridges, little pouches of the bladder lining, the mucosa, can push outward.

These are called cellules.

Cellules, like little cells.

Sort of.

But the really important thing is if these couches push all the way through the muscle wall, they form diverticula.

Diverticula.

Why are those so significant?

What's the risk?

Huge risk for infection, and also for stone formation.

Diverticula are like little side pockets that the bladder muscle can't squeeze empty.

Ah, so urine just sits there.

Exactly.

Stagnant urine is a breeding ground for bacteria.

So seeing diverticula tells you the obstruction is likely chronic and the infection risk is high.

But this compensation can't last forever, right?

No.

Eventually, the muscle gets tired.

It enters the decompensatory stage.

The detrusor becomes fatigued.

It can't contract effectively anymore.

So what happens then?

Residual urine volume starts to climb dramatically.

The urinary stream becomes weak, intermittent, maybe just dribbling.

And the hallmark symptom of this stage is overflow incontinence.

Overflow.

Meaning it just spills out.

Pretty much.

The bladder gets so full and overstretched that the pressure inside finally just overcomes the urethral resistance and urine leaks out, but without a proper detrusor contraction.

Okay, that makes sense.

Now let's shift gears from plumbing problems to wiring problems.

Neurogenic bladder disorders.

Right.

Here the issue isn't a physical blockage, but damage to the nerves controlling the bladder.

We usually categorize these based on where the nerve damage, the lesion, is located relative to that sacral maturetion center in the lower spinal cord.

Okay.

What's the first type?

First is the spastic bladder.

Think spastic as in hyperactive.

This results from lesions above the sacral center, often from spinal cord injuries higher up, or things like strokes or multiple sclerosis.

So above the basic reflex center, what does that do?

It means the bladder loses the inhibitory control from the brain and the pons.

So the basic sacral reflex runs wild.

The bladder becomes hyperactive.

It contracts frequently and involuntarily, often with low capacity.

It essentially fails to store urine properly.

It's often a high pressure situation inside the bladder too.

High pressure.

That sounds risky for the kidneys again.

Very risky.

And there's another specific danger with lesions high up, particularly in the cervical spinal cord,

autonomic hyperreflexia.

Oh, right.

You mentioned that.

What triggers it?

It can be triggered by stimuli below the level of the injury that the person can't feel, like a full bladder, a kinked catheter, even constipation or a skin irritation.

And what happens?

The body below the injury sends signals up, but they get blocked.

This triggers a massive, uncontrolled sympathetic nervous system response above the level of the injury.

That sounds alarming.

What are the signs?

Is it just high blood pressure?

It's a medical emergency.

You see a sudden severe spike in blood pressure, often accompanied by a pounding headache,

profuse sweating and fleshing above the level of lesion, goosebumps, blurred vision, and sometimes a slowed heart rate, bradycardia, as the body tries to compensate.

It needs immediate attention.

Wow.

Okay.

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

What about lesions at or below it?

That leads to the second type, the flaccid bladder.

Think flaccid, as in sloppy or weak.

This happens with damage to the sacral micturition center itself, or the nerves coming out of it.

Common causes include spinal cord injuries at the sacral level, or peripheral neuropathies like those seen in diabetes.

So what does a flaccid bladder do, or rather not do?

It loses its muscle tone.

It becomes a tonic.

You can stretch out enormously to hold huge volumes of urine, but it can't contract effectively to empty.

Plus, the person often loses the sensation of bladder fullness.

So it fails to empty urine.

Okay.

So spastic fails to store, flaccid fails to empty.

Are the treatment goals different?

The underlying problem is different, but the main goals of treatment are actually pretty similar for both.

Number one, prevent bladder over -distension.

Number two, prevent urinary tract infections, UTIs.

And number three, most importantly, protect the kidneys from damage due to high pressure or reflux.

How do they achieve that?

Often involves things like intermittent catheterization, regularly emptying the bladder with a catheter.

Sometimes bladder retraining schedules.

And pharmacologic approaches, maybe using drugs to relax the external sphincter in some cases, or drugs to stimulate contraction in a flaccid bladder, though that can be tricky.

All right.

Let's talk about incontinence itself, the involuntary loss of urine.

You said it's really common.

Oh, incredibly common.

It affects millions of people, especially as they get older.

And it's roughly twice as common in women compared to men.

Okay.

Let's break down the main types.

What's the first one?

Probably the one people think of most often.

Stress incontinence.

This is leakage that happens with increased abdominal pressure, like when you cough, laugh, sneeze, lift something heavy, or exercise.

What's the mechanism there?

Why does that pressure cause leakage?

It's usually due to weakness in the pelvic floor muscles and the urethral sphincter.

In women, a key factor is the loss of support for the blighter neck and urethra.

Normally there's a specific angle, the posterior urethravesical angle, or PUV angle.

This angle helps ensure that when abdominal pressure rises,

it squeezes the urethra closed even tighter.

But if the pelvic floor is weak, that angle gets lost or flattened.

So the pressure increase doesn't close the valve anymore.

Exactly.

The pressure increase pushes urine out instead of sealing the urethra shut.

Got it.

What's the next type?

Next is overactive bladder, or OAB, which often leads to urge incontinence.

This is characterized by that sudden, intense urge to urinate urgency,

often followed by an involuntary bladder contraction and leakage before you can make it to the bathroom.

Why does the bladder suddenly get so urgent?

Well, there are two main theories.

The neurogenic theory suggests it's due to damage or changes in the central nervous system pathways that normally inhibit bladder contractions during filling.

So less inhibition from the brain.

Kind of, yeah.

The myogenic theory focuses on the bladder muscle itself.

It suggests the smooth muscle cells become inherently more excitable, hypersensitive, maybe developing abnormal electrical activity that triggers contractions too easily.

Interesting.

Okay.

Type three.

Type three is overflow incontinence.

We actually touched on this with decompensated obstruction.

This is leakage that occurs when the bladder is overly full and distended and the pressure just passively overcomes the outlet resistance.

Importantly, it happens without an actual detrusor contraction.

So causes would be like that enlargement again, or maybe severe constipation blocking the outlet.

Precisely.

Or a flaccid neurogenic bladder that just can't empty itself.

Okay.

And the last type.

Finally, there's functional incontinence.

This one isn't about a problem with the bladder or urethra itself.

It's when urine loss happens because of factors outside the urinary tract.

Like what kind of factors?

Things like mobility problems.

Someone physically can't get to the toilet fast enough or cognitive impairment like dementia or the person might not recognize the need to go or how to use the toilet.

Environmental barriers too.

Right.

So managing incontinence, it sounds like it really depends on the type.

Absolutely.

Diagnosis is key.

Things like keeping avoiding diary,

specific questionnaires, and sometimes provocative stress testing, like asking someone to crawl forcefully with a full bladder, can help pinpoint the type.

And treatment.

Behavioral therapies are often first line, especially for stress and urgent continents.

Things like scheduling toilet trips, managing fluid intake, and critically, Kegel exercises.

Ah, Kegels.

Those are for strengthening the pelvic floor, right?

Exactly.

Strengthening those muscles provides better support for the urethra and bladder neck, which is crucial for stress incontinence, but can also help suppress urgency in OAB.

And you mentioned something specific for older adults.

A mnemonic.

Yes.

Especially when incontinence appears suddenly in an older person, it's vital to check for potentially reversible transient causes before jumping to conclusions about permanent incontinence.

We use the mnemonic diapers.

Diapers.

Okay.

That sounds useful.

Let's run through it.

Sure.

D is for dementia or delirium.

I is for infection, urinary tract infection, or even vaginal infections.

A is for atrophic vaginitis or urethritis thinning and irritation of tissues due to low estrogen.

P is for pharmaceutical agents.

So many drugs can affect bladder function.

Diuretics, sedatives, anticholinergics, alpha blockers.

Right.

The P is doubled.

Yes.

The second P is for psychological causes like severe depression.

E is for endocrine conditions,

especially poorly controlled diabetes, which can cause increased urine production and nerve damage.

R is for we mentioned that under functional incontinence.

And S is for stool impaction.

Severe constipation can physically press on the bladder outlet or irritate the nerves.

That's fantastic.

Diapers.

So addressing any of those underlying issues might resolve the incontinence.

Often, yes.

It's a really valuable checklist for clinicians working with older adults.

Okay.

Our final topic for this deep dive, cancer of the bladder.

How common is this compared to other urinary tract issues?

It's actually the most frequent type of urinary tract cancer in the United States.

It typically arises from the urothelial cells, the transitional cells that line the inside of the bladder.

And being cancer of a storage organ.

Does that mean the cause is related to what's in the urine?

Very much so.

It's strongly linked to carcinogens that are filtered by the kidneys and then sit in contact with the bladder lining for extended periods.

So what are the biggest risk factors we absolutely need to remember?

Number one, without a doubt, is cigarette smoking.

Smokers have a significantly higher risk.

Okay.

Smoking.

What else?

The other major one is occupational exposure to certain industrial chemicals,

specifically aromatic amines.

These were historically common in industries like dye manufacturing, rubber processing, textiles, and chemicals.

So carcinogens concentrating in the urine,

irritating the lining over time.

Exactly.

What's the most common way bladder cancer presents itself?

What's the sign to watch for?

The absolute key clinical manifestation, the one everyone needs to know, is painless hematuria.

Blood in the urine, but no pain associated with it.

Correct.

It might be gross hematuria, meaning visible blood, or microscopic, only found on a urine test.

Crucially, this bleeding is often intermittent.

It comes and goes.

And that probably leads to delays in diagnosis, right?

If it stops, people might think it was nothing.

Precisely.

That intermittent nature is a major reason why diagnosis can sometimes be delayed, which is unfortunate because early detection is key.

How does the prognosis look?

Does it vary?

It varies tremendously based on the grade and stage of the tumor.

Low -grade tumors that haven't invaded the bladder muscle wall, non -invasive, generally have an excellent prognosis, although they do tend to recur, requiring ongoing surveillance.

Okay.

But high -grade tumors, especially those that have invaded into or through the detrusor muscle, are much more dangerous.

They have significantly higher risk of metastasizing, spreading to other parts of the body.

How is it diagnosed and treated?

Diagnosis usually involves urine cytology, looking for cancer cells in the urine,

cystoscopy, inserting a camera into the bladder to look directly at the lining,

and biopsy, taking tissue samples.

And treatment depends on that invasiveness.

Entirely.

For superficial, non -invasive tumors,

treatment might just be endoscopic resection, basically scraping the tumor off the bladder wall during cystoscopy, sometimes followed by intravysical therapy, putting chemotherapy or immunotherapy directly into the bladder.

But for the invasive ones?

For muscle -invasive cancer, the standard treatment is often much more aggressive, a radical cystectomy.

Removing the entire bladder?

Yes.

Surgical removal of the bladder, often along with nearby lymph nodes and related structures.

And obviously, if you remove the bladder, you need to create a new way for urine to exit the body, some form of urinary diversion.

Like an ileal conduit or a neoblader.

Hashtag outro.

Wow.

Okay.

We have covered a lot of ground there.

From the intricate neural control.

That whole ballet of nerves.

To distinguishing those key neurogenic problems.

The spastic fail -to -store bladder versus the flaccid fail -to -empty one.

Right.

And then navigating the four main types of incontinence, stress, urge, overflow, and functional.

Plus that really useful diapers mnemonic.

And finishing up with bladder cancer.

Remembering smoking and painless hematuria as the key takeaways.

It's a dense chapter, definitely.

It is.

But hopefully breaking it down by focusing on that core balance storage versus emptying and linking the symptoms back to the underlying mechanisms helps make it click.

Absolutely.

So maybe a final thought to leave you with, building on all this.

We talked about how common things like stress incontinence and bladder are, right?

Yeah.

Huge numbers.

And we know that relatively simple non -invasive behavioral treatments like Kegel exercises can be really effective for many people.

Right.

So thinking about that, here's the question.

What kind of immediate changes could we realistically make in, say, public health messaging or primary care education?

To truly empower more people to try and improve their bladder function with these behavioral strategies first.

Potentially delaying or avoiding the need for medications or surgery later on.

That's a great point.

How do we get that information and empowerment out there more effectively?

Food for thought.

Well, thank you for walking us through all of that.

And thank you for joining us on this deep dive into chapter 35.

We really hope this map helps you navigate the material.