S8: micturition & incontinence

Question 1

What are the two phases of micturition?

Answer 1

Micturition – process of eliminating water and electrolytes from the urinary system
Storage/continence phase: urine is stored in the bladder
Voiding phase: urine is released through the urethra

Question 2

Describe the sympathetic innervation in the storage phase

Answer 2

Signals are sent from the L centre (pontine continence centre) to sympathetic nuclei -> detrusor muscle and internal urethral sphincter
At the bladder this stimulates:
-relaxation of the detrusor in the bladder wall – via stimulation of B3-adrenoreceptors
-contraction of the IUS – via stimulation of A1-adrenoreceptors at neck of bladder

Question 3

Describe the sensory innervation in the storage phase

Answer 3

Senses the bladder stretch
Stimulates the sympathetic action
Communicates with cerebral cortex – conscious appreciation for how full our bladder is

Question 4

Describe the somatic innervation in the storage phase

Answer 4

EUS is under voluntary somatic control
Impulses travel to the EUS via the pudendal nerve to nicotinic receptors on the striated muscle -> contraction of the EUS, which prevents any urine from leaking out

Question 5

Describe the parasympathetic innervation in the voiding phase

Answer 5

Upon voluntary decision to urinate, neurones of the M centre fire to excite the sacral preganglionic neurones
Subsequent parasympathetic stimulation causes a release of acetylcholine -> works on M3 receptors on the detrusor muscle -> contract & increases intra-vesicular pressure

Question 6

Describe the sensory innervation in the voiding phase

Answer 6

Senses the bladder stretch
Stimulates the parasympathetic action (positive feedback loop)
If stretch is high enough, directly communicates with M centre which causes activation of parasympathetics

Question 7

Explain why we do not micturate even when bladder is full

Answer 7

M centre is not autonomous – conscious control of it
Paracentral lobules (medial side of cerebral cortex) send both excitatory and inhibitory influences onto the M centre = voluntary decision is made here 
M centre sends inhibitory connections to the L centre – when you decide to void, inhibits the L centre -> relaxation of the external urethral sphincter due to pudendal nerve being turned off

Question 8

What is stress urinary incontinence?

Answer 8

Complaint of involuntary leakage on effort or exertion, or on sneezing or coughing

Question 9

What is urgency urinary incontinence?

Answer 9

Complaint of involuntary leakage accompanied by or immediately proceeded by urgency

Question 10

What is mixed urinary incontinence?

Answer 10

Complaint of involuntary leakage associated with urgency and also with exertion, effort, sneezing or coughing

Question 11

What is overflow incontinence?

Answer 11

Involuntary release of urine when the bladder becomes overly full – due to weak bladder muscle or blockage

Question 12

What is an overactive bladder?

Answer 12

Frequent or sudden urge to urinate that may be difficult to control

Question 13

List the risk factors for urinary incontinence

Answer 13

Pregnancy and childbirth 
Obesity 
Pelvic prolapse 
Race 
Pelvic surgery/DXT

Question 14

Describe the initial investigation of patients with urinary incontinence

Answer 14

Urine dipstick – rule out other differentials
Basic non-invasive urodynamics – frequency-volume chart, bladder diary, post-micturition residual volume
Optional – invasive urodynamics, pad tests & cystoscopy

Question 15

Describe the initial management of patients with urinary incontinence

Answer 15

Conservative management – modify fluid intake, weight loss, stop smoking, decrease caffeine intake, avoid constipation, timed voiding
Contained incontinence – patients who are unsuitable for surgery who have failed conservative management: indwelling catheter, sheath & incontinence pads

Question 16

Describe specific management for stress urinary incontinence

Answer 16

Pelvic floor muscle training
Duloxetine – combined noradrenaline & serotonin uptake inhibitor (increased activity in the EUS during filled phase)
Surgery:
-females: permanent intention – open retropubic suspension procedures/classical autologous sling procedures; temporary intention – intramural bulking agents
-males: artificial urinary sphincter & male sling procedure

Question 17

Describe the male artificial urinary sphincter

Answer 17

Gold standard
Urethral sphincter deficiency
Cuff stimulates action of normal sphincter to circumferentially close the urethra

Question 18

Describe the initial management for urge urinary incontinence

Answer 18

Bladder training – at least 6 weeks duration
Schedule of voiding: void every hour during the day, must not void in between, intervals increased by 15-30 mins until interval of 2-3 hours is reached

Question 19

Describe pharmacological management of urge urinary incontinence

Answer 19

Anticholinergics – act on muscarinic receptors (M2,M3)
Side effects due to effects on M receptors at other sites
B3-adrenoreceptor agonist – mirabegron

Question 20

Describe botulism toxin

Answer 20

Potent biological neurotoxin
Inhibits release of ACh at pre-synaptic neuromuscular junction causing targeted flaccid paralysis
Duration of action 3-6 months

Question 21

List surgical intervention of urge incontinence

Answer 21

Sacral nerve neuromodulation
Autoaugmentation
Augmentation cystoplasty
Urinary diversion

Question 22

What is enuresis?

Answer 22

Bedwetting = involuntary wetting during sleep at least 2x/week in children > 5 years with no CNS defects
Primary – never achieved sustained continence at night
Secondary – restarted having been dry at night for 6+ months

Question 23

How do you manage enuresis in children?

Answer 23

Primary without daytime symptoms – usually managed in primary care -> reassurance & positive reward system
Primary with daytime symptoms – caused by disorders of the lower urinary tract
Secondary – treat underlying cause if it has been identified eg. UTIs, constipation, diabetes, psychological problems etc