Micturition and Disorders of Urination (Week 6--Eslami)

Question 1

Micturition

Answer 1

Urination

Question 2

Smooth muscle of the bladder

Answer 2

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)

Question 3

Is there skeletal muscle in the bladder?

Answer 3

Only the external sphincter is skeletal muscle (under voluntary control)

Question 4

2 phases of activity of the lower urinary tract

Answer 4

Storage: internal sphincter tense, detrusor muscle relaxed (sympathetic)

Voiding: internal sphincter relaxed, detrusor muscle contracted (parasympathetic)

Question 5

Which PNS fibers innervate which parts of the bladder?

Answer 5

Pelvic splanchnic nerves (S2-4)

Contract bladder to void/urinate

Use muscarinic receptors (M2, M3)

Question 6

Which SNS fibers innervate which parts of the bladder?

Answer 6

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

(Lumbar plexus (L1-3) and hypogastric nerves (T11-L2) innervate internal sphincter to constrict and detrusor muscle to relax)

Question 7

Which afferent fibers innervate the bladder?

Answer 7

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)

Question 8

What is the first thing to happen when you urinate?

Answer 8

External sphincter relaxes (this is voluntary/skeletal muscle controlled by pudendal nerve (S2-4))

Question 9

What is bladder capacity?

Answer 9

Capacity is normally 300-600cc

First urge to void is 150-300cc

Question 10

Muscarinic receptors in the bladder

Answer 10

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

Question 11

Urinary changes with normal aging

Answer 11

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)

Question 12

How does estrogen deficiency after menopause affect women?

Answer 12

Estrogen deficiency reduces effectiveness of internal and external urethral sphincter

Estrogen deficiecny predisposes to urethritis, trigonitis, cystitis

Vaginal atrophy occurs when estrogen deficiency

Question 13

Which structures of lower urinary tract in women have estrogen receptors?

Answer 13

Trigone of bladder

Urethra

Pelvic floor muscles

Question 14

What can prostate enlargement do to the bladder in men?

Answer 14

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

Question 15

4 types of urinary incontinence

Answer 15

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

Question 16

What would an anti-cholinergic drug cause regarding incontinence?

Answer 16

Inhibit bladder contractions and result in urinary retention (too little PNS)

Overflow urinary incontinence

Ex: Elavil (amitriptyline)

Question 17

What would a cholinergic type medication cause regarding incontinence?

Answer 17

Causes involuntary/overactive bladder contractions (too much PNS)

Urge type urinary incontinence

Question 18

What would an alpha adrenergic agonist cause regarding incontinence?

Answer 18

Internal urethral sphincter would constantly be closed (too much SNS)

Overflow urinary incontinence

Question 19

What would an alpha adrenergic blocker do regarding urinary incontinence?

Answer 19

Unable to close internal sphincter (too little SNS)

Stress type urinary incontinence

Question 20

What kind of medication do you give a man with an enlarged prostate who is suffering from irritative symptoms (urgency, frequency)?

Answer 20

Alpha adrenergic blocker (teraxosin, doxazosin, tamsulosin) to relax internal sphincter and allow for more efficient bladder emptying with each void

Question 21

Vesical plexus

Answer 21

Autonomic fibers in vesical plexus innervate lower ureter, urinary bladder, internal urethral sphincter, prostatic urethra (male)

Question 22

2 targets of sympathetic fibers

Answer 22

1) Internal urethral sphincter (alpha receptors to constrict sphincter)
2) Dome of urinary bladder (beta receptors to relax; less significant effect)

Question 23

Mechanisms to ensure that urine doesn’t leak out when intravesical pressure increases

Answer 23

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

Question 24

Why do females get stress urinary incontinence more than males?

Answer 24

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