Smooth muscle of the bladder
Detrusor muscle is lined with superficial layer of transitional epithelium then multiple layers of stratified cuboidal cells underneath
Internal sphincter is smooth muscle (not a true sphincter)
Is there skeletal muscle in the bladder?
Only the external sphincter is skeletal muscle (under voluntary control)
2 phases of activity of the lower urinary tract
Storage: internal sphincter tense, detrusor muscle relaxed (sympathetic)
Voiding: internal sphincter relaxed, detrusor muscle contracted (parasympathetic)
Which PNS fibers innervate which parts of the bladder?
Pelvic splanchnic nerves (S2-4)
Contract bladder to void/urinate
Use muscarinic receptors (M2, M3)
Which SNS fibers innervate which parts of the bladder?
(Lumbar plexus (L1-3) and hypogastric nerves (T11-L2) innervate internal sphincter to constrict and detrusor muscle to relax)
Sacral sympathetic splanchnic nerves T10-L2
Storage of urine
Uses alpha adrenergic receptors; also beta-2 receptors relax bladder to allow more filling (but this is minor), and DON'T influence detrusor muscle contractility
Which afferent fibers innervate the bladder?
Mechanoreceptors in bladder wall sense fullness and send afferent fibers through pelvic and hypogastric nerves that are located in dorsal root ganglia at S2-4 and T11-L2
Then, info sent via spinal cord to pontine micturition center and cerebral cortex and voluntary signal occurs via pontine micturition center
(Then parasympathetic neurons contract detrusor and relax internal sphincter, and somatic motor via pudenal nerve inhibited which allows external sphincter to open and urine flows out)
What is the first thing to happen when you urinate?
External sphincter relaxes (this is voluntary/skeletal muscle controlled by pudendal nerve (S2-4))
What is bladder capacity?
Capacity is normally 300-600cc
First urge to void is 150-300cc
Muscarinic receptors in the bladder
M2: indirectly modulate detrusor contraction by inhibiting cAMP that is increased by beta receptors; most abundant in bladder; in brain, smooth muscle and heart
M3: directly mediate detrusor contraction; in brain, smooth muscle and exocrine glands (salivary glands)
Both muscarinic receptors are parasymp (obvi), contraction, urination
Urinary changes with normal aging
Decrease in bladder capacity and force of contractions
Decrease in ability to postpone voiding (frequency)
Decrease in urethral compliance
Decrease in strength of pelvic support muscles
Increase in post-void residual volume
Increase in involuntary bladder contractions (urgency)
Increase in nocturia (1-2x per night)
How does estrogen deficiency after menopause affect women?
Estrogen deficiency reduces effectiveness of internal and external urethral sphincter
Estrogen deficiecny predisposes to urethritis, trigonitis, cystitis
Vaginal atrophy occurs when estrogen deficiency
Which structures of lower urinary tract in women have estrogen receptors?
Trigone of bladder
Pelvic floor muscles
What can prostate enlargement do to the bladder in men?
Prostate enlargement can cause frequency or urgency because of irritation of prostate on bladder
Prostate enlargement can cause hesitancy or decrease in force of urine stream because of obstruction as urethra passes through prostate gland
4 types of urinary incontinence
1) Urge incontinence: hypersensitivity of detrusor muscle; when bladder fills, brain thinks you have to go even if this is low volume and they end up leaking urine; due to bladder infection, bladder stone, etc
2) Overflow incontinence: either underactive bladder so no signals to empty and bladder blows up, or obstruction so urine can't get out and bladder blows up (BPH)
3) Stress incontinence: weak support of levator ani muscles and fascial ligaments causes increase in intraabdominal pressure to be transmitted to bladder and not urethra so urine leaks when sneeze, cough, jog; common in women
4) Functional incontinence: mental or physical disabilities but urinary system is fine; Parkinson's, Alzheimer's, depression
What would an anti-cholinergic drug cause regarding incontinence?
Inhibit bladder contractions and result in urinary retention (too little PNS)
Overflow urinary incontinence
Ex: Elavil (amitriptyline)
What would a cholinergic type medication cause regarding incontinence?
Causes involuntary/overactive bladder contractions (too much PNS)
Urge type urinary incontinence
What would an alpha adrenergic agonist cause regarding incontinence?
Internal urethral sphincter would constantly be closed (too much SNS)
Overflow urinary incontinence
What would an alpha adrenergic blocker do regarding urinary incontinence?
Unable to close internal sphincter (too little SNS)
Stress type urinary incontinence
What kind of medication do you give a man with an enlarged prostate who is suffering from irritative symptoms (urgency, frequency)?
Alpha adrenergic blocker (teraxosin, doxazosin, tamsulosin) to relax internal sphincter and allow for more efficient bladder emptying with each void
Autonomic fibers in vesical plexus innervate lower ureter, urinary bladder, internal urethral sphincter, prostatic urethra (male)
2 targets of sympathetic fibers
1) Internal urethral sphincter (alpha receptors to constrict sphincter)
2) Dome of urinary bladder (beta receptors to relax; less significant effect)
Mechanisms to ensure that urine doesn't leak out when intravesical pressure increases
Fascial supports anchor neck of bladder to pubic bones so increased intraabdominal pressure transmitted equally to bladder and urethra--maintaining gradient
Levator ani muscles contract when abdominal pressure increased and this directly compresses urethra
Why do females get stress urinary incontinence more than males?
Because female UG diaphragm has another opening for vagina
If levator ani and fascial ligaments are lax (women who have had babies), neck of bladder can descend and increases in intraabdominal pressure transmitted to bladder more than urethra and that gradient is not maintained so urine leaks out
"Stress" because when you put stress on the bladder (sneeze, cough, jog) you leak urine