Urinary Bladder Physiology

This set of flashcards covers key vocabulary and concepts related to urinary bladder physiology.

Urinary Bladder

A temporary storage organ for urine that can expand as it fills and contracts to empty.

Trigone

The smooth triangular area between the openings of the ureters and urethra within the bladder.

Detrusor Muscle

The smooth muscle layer of the bladder wall that contracts to expel urine.

Micturition reflex

The reflex that results in the involuntary emptying of the urinary bladder.

Cystometrogram

A plot of intravesical pressure against bladder volume used to assess bladder function.

Cerebral Cortex

The area of the brain that modulates micturition signals for voluntary control over urination.

Pudendal Nerve

A somatic nerve that controls voluntary contraction of the external urethral sphincter.

Internal Urethral Sphincter

The smooth muscle sphincter that is involuntary and helps retain urine in the bladder.

External Urethral Sphincter

The skeletal muscle sphincter that is voluntary and allows for conscious control over urination.

Neurogenic Bladder

Bladder dysfunction caused by a problem with the nervous system, leading to issues like incontinence.

Atonic Bladder

A hypotonic bladder condition resulting from neurological damage leading to loss of control.

Overactive Bladder Syndrome

A condition characterized by urinary urgency, frequent urination, and sometimes incontinence.

Sympathetic Nerve Supply

Nerves that inhibit bladder contraction and promote internal urethral sphincter closure.

Parasympathetic Nerve Supply

Nerves that stimulate detrusor contraction and relaxation of the internal urethral sphincter.

Urinary Incontinence

Loss of bladder control, resulting in involuntary leakage of urine.

Painful Bladder Syndrome

A chronic condition causing bladder pain, urgency, and frequent urination due to pelvic sensitivity.

What is “micturition” (the lecture called it “Patricia” by mistake)?

The process of filling the bladder with urine and then voiding (urinating).

What is “voiding”?

Emptying the bladder by coordinated detrusor contraction and sphincter relaxation.

Main function of the urinary bladder?

Storage organ for urine (a hollow muscular reservoir).

Where is the bladder when empty vs full?

Empty: pelvic cavity. Full: expands upward into the abdominal cavity.

Bladder position in babies vs older children?

Higher in abdomen at birth; descends into pelvis by about 5–6 years.

What are bladder rugae (folds) for?

Allow stretching/expansion as bladder volume increases.

What is the trigone?

A smooth triangular area between ureter openings and the urethral outlet.

Why is the trigone smooth (not folded)?

Helps urine funnel out efficiently during voiding.

What is the detrusor muscle?

The thick smooth muscle wall of the bladder responsible for contraction in voiding.

Purpose of urethral sphincters?

Act like locks to prevent leakage during storage.

Key anatomical difference affecting urination in males vs females?

Urethra length: male long (through penis); female short.

Clinical implication of short female urethra?

Higher risk of ascending infections/UTIs.

Do women have an internal sphincter?

Yes; but it may be a more complex structure than in males.

How can enlarged prostate affect urination?

Can compress outlet region causing urgency; weak stream; retention; and difficulty voiding.

Three nervous system components controlling bladder function?

Sympathetic; parasympathetic; somatic.

Sympathetic nerve name and spinal level?

Hypogastric nerve; mainly lumbar.

Parasympathetic nerve name and spinal level?

Pelvic nerves; mainly sacral.

Somatic nerve name and target?

Pudendal nerve; external urethral sphincter (skeletal muscle).

Sympathetic function during storage?

Promotes filling: detrusor relaxes; internal sphincter contracts.

Parasympathetic function during voiding?

Promotes emptying: detrusor contracts; internal sphincter relaxes.

Somatic function during continence?

Keeps external sphincter contracted to prevent leakage.

Which part is under conscious control?

Mostly somatic control of the external sphincter via the pudendal nerve.

What does “potty training” physiologically mean?

Learning voluntary control of pudendal nerve/external sphincter plus CNS coordination.

Main neurotransmitter for sympathetic bladder control?

Noradrenaline (norepinephrine).

Sympathetic receptor on detrusor and effect?

β3 adrenergic receptor → detrusor relaxation.

Sympathetic receptor at bladder outlet/urethra and effect?

α1 adrenergic receptor → outlet contraction/closure.

Main neurotransmitter for parasympathetic voiding?

Acetylcholine (ACh).

Parasympathetic receptor driving detrusor contraction?

Muscarinic M3 receptor → detrusor contraction.

Somatic receptor at external sphincter?

Nicotinic ACh receptors → skeletal muscle contraction.

Approx volume for first urge to void?

About 150–300 mL.

Approx volume for “fullness” sensation?

About 300–400 mL.

Approx volume for discomfort?

About 400–600 mL.

Approx volume where pain appears?

Around 700 mL (approaching limit).

What happens when bladder gets too full/painful?

Protective reflex overrides voluntary control → voiding occurs to prevent damage.

Storage state: detrusor/internal sphincter/external sphincter?

Detrusor relaxed; internal sphincter contracted; external sphincter contracted.

Voiding state: detrusor/internal sphincter/external sphincter?

Detrusor contracted; internal sphincter relaxed; external sphincter relaxed (voluntary release).

Which system dominates storage?

Sympathetic plus somatic.

Which system dominates voiding?

Parasympathetic (with somatic release).

Which brainstem region coordinates micturition reflex (mentioned)?

Pons (pontine micturition center concept).

Why can delaying urination become painful?

Stretch activates nociceptors in bladder wall; afferent signaling via pelvic pathways.

What is cystometry/cystometrogram used for?

Assess bladder function: sensation and pressure during filling and voiding.

How is cystometry done (basic)?

Catheters: one measures pressure; another infuses saline to fill bladder.

What can cystometry detect conceptually?

Abnormal pressure/urge patterns such as detrusor overactivity.

What happens to bladder function with ageing (general)?

More detrusor overactivity; reduced flow; weaker muscle control.

How can menopause contribute to urinary issues?

Lower estrogen → urogenital atrophy → worsened continence symptoms.

How can BPH affect bladder symptoms?

Outlet obstruction → frequency/urgency/retention and weaker stream.

What is an atonic/flaccid (“hypotonic”) bladder conceptually?

Weak detrusor → poor emptying → overflow incontinence/dribbling.

What is automatic/spastic neurogenic bladder after spinal cord transection?

Reflex voiding returns after weeks but no voluntary control.

What is nocturnal enuresis (bedwetting) linked to here?

Immature nervous control/myelination delaying external sphincter control.

What is overactive bladder (core idea)?

Detrusor overactivity/instability → urgency; frequency; nocturia ± urge incontinence.

Possible neurological associations mentioned for OAB?

Stroke; spinal injury; multiple sclerosis.

Drug classes mentioned that can worsen urinary symptoms?

ACE inhibitors; angiotensin antagonists; antipsychotics; diuretics; opioids.

Main med class used for OAB and target?

Antimuscarinics block M3-mediated detrusor contraction.

Another OAB drug strategy and target?

β3 agonists promote detrusor relaxation during filling.

OAB in menopause: what can help?

Vaginal estrogen can reduce atrophic changes and improve symptoms.

Where is the main micturition control centre located?

Pontine micturition centre (PMC) in the brainstem.

Which brain regions receive bladder afferent signals?

Parietal lobes and thalamus.

Which brain regions provide inhibitory control over micturition?

Frontal lobes and basal ganglia.

What is the role of cortical centres in voluntary voiding?

Stimulate sacral micturition centre and inhibit pudendal nerve.

What happens to the pudendal nerve during voluntary voiding?

It is inhibited causing relaxation of the external urethral sphincter.

What reflex loop is essential for micturition?

Afferent–efferent pelvic nerve loop.

Which nerve carries stretch receptor signals from the bladder?

Pelvic nerve (parasympathetic afferents).

Why does increased abdominal pressure help voiding?

It increases intravesical pressure by contracting abdominal muscles and diaphragm.

Why does intravesical pressure stay low during early bladder filling?

High bladder compliance due to detrusor relaxation.

What does bladder compliance describe?

Ability of bladder to accommodate volume with minimal pressure increase.

What happens to compliance near bladder capacity?

Compliance decreases and pressure rises sharply.

What is a cystometrogram?

A graph of intravesical pressure versus bladder volume.

What does the basal cystometrogram represent?

Passive bladder filling without detrusor contractions.

What do pressure waves during filling on cystometrogram indicate?

Micturition reflex activity.

What does the steep pressure rise during voiding on cystometrogram indicate?

Active detrusor contraction.

How does urine leave the female urethra after voiding?

By gravity.

How is residual urine expelled from the male urethra?

By contractions of the bulbocavernosus muscle.

Why is male voiding more mechanically complex?

Longer urethra and need for skeletal muscle contractions.

What defines spinal shock–related bladder dysfunction?

Temporary loss of reflexes after acute spinal cord injury.

When does automatic bladder function return after spinal shock?

After about 2–6 weeks.

Why is automatic bladder called spastic neurogenic bladder?

Reflex voiding occurs without voluntary cortical control.

What causes uninhibited neurogenic bladder?

Loss of inhibitory brainstem control over sacral centres.

Key feature of uninhibited neurogenic bladder?

Small volumes trigger immediate micturition reflex.

What nerve damage causes atonic (hypotonic) bladder?

Damage to dorsal sacral sensory roots.

Why do antimuscarinic drugs worsen atonic bladder?

They further reduce already weak detrusor activity.

Why are cholinergic agonists ineffective in atonic bladder?

Detrusor muscle responsiveness is impaired.

Why does voiding become harder with age?

Reduced detrusor contractility and neural coordination.

Why does nocturia increase in older adults?

Shift in diurnal urine production plus comorbidities and medications.

What happens to urethral mucosal seal after menopause?

It weakens due to estrogen loss leading to reduced continence.