Micturition

Question 1

Describe the micturition reflex

Answer 1

As the bladder dissents during filling this activates stretch receptors in the wall of the detrusor muscle; these provide sensory feedback to the micturition centre in the pons via the pelvic nerves (S2-4). The micturition centre assess social factors as if it is deemed acceptable to urinate, it will send parasympathetic signals to the detrusor muscle via the pelvic nerves (S2-4) which allows bladder contraction and sphincter relaxation (via B3). If it is not deemed acceptable to urinate, somatic innervation to the external urethral sphincter is maintained by the pudendal nerve.

Question 2

What stimulates contraction of the bladder?

Answer 2

Release of ACh from parasympathetic nerve fibres of the pelvic nerves. This ACh binds to the M3 (muscarinic 3) receptor on the detrusor muscle which stimulates contraction.

Question 3

What are the three main groups/types of micturition disorder that can occur?

Answer 3

Anatomical (e.g. obstruction due to BPH), functional (MS or PD) and medical (cardiac, hepatic or renal failure etc.)

Question 4

How may caffeine lead to increased urinary frequency?

Answer 4

Caffeine leads to the release of calcium stores from the golgi apparatus in the bladder wall which makes bladder contraction more likely

Question 5

Explain the mechanism of action of alpha blockers in the treatment of micturition disorders

Answer 5

Prevent the action of the sympathetic nervous system on the internal urethral sphincter and therefore the sphincter remains flaccid which aids in the passage of urine

Question 6

Explain the mechanism of action of 5a reductase inhibitors in the treatment of micturition disorders

Answer 6

These drugs prevent the conversion of testosterone into DHT which is the primary molecule involved in prostatic growth and therefore this prevents prostatic growth and causes atrophy which is useful in the treatment of BPH

Question 7

What symptoms may be associated with storage disorders of the lower urinary tract?

Answer 7

increased urinary frequency, nocturia, urgency and urge incontinence

Question 8

What symptoms may be associated with voiding disorders of the lower urinary tract?

Answer 8

hesitancy, straining, poor urinary flow, intermittency, poor flow or incomplete emptying as well as terminal dribbling, dysuria and haematuria

Question 9

What symptoms may be associated with overactive bladder syndrome (OAB)?

Answer 9

• Urinary Urgency (with or without incontinence)
• Urinary Frequency
• Nocturia sometimes

Question 10

What are the two types of urinary incontinence?

Answer 10

Stress and urge urinary incontinence

Question 11

What is stress urinary incontinence?

Answer 11

leakage on effort or exertion due to increased abdominal pressure

Question 12

What is urge urinary incontinence?

Answer 12

Leakage caused by urgency

Question 13

What treatments may be given for overactive bladder syndrome?

Answer 13

Anticholinergics, B3 adrenergic or botox

Question 14

Explain how anticholinergics (oxybutyrin) work to alleviate overactive bladder syndrome

Answer 14

These block Ach in the parasympathetic nerves (in order to prevent detrusor muscle contraction and EUS relaxation) but these may also block these receptors elsewhere too, such as the salivary glands and can cause dry mouth

Question 15

Explain how B3 adrenergic agonists (Mirabegron) work to alleviate overactive bladder syndrome

Answer 15

B3 adrenoreceptors are upregulated in OAB and therefore this treatment can be effective but can lead to vasoconstriction and therefore hypertension may become an issue

Question 16

Explain how botulinum toxin A (botox) works to alleviate overactive bladder syndrome

Answer 16

This drug fuses the synaptic vesicles with the motor end plate but these drugs can lead to issues with hypercontinence (inability to urinate)

Question 17

What lesions of the spinal cord would be ‘safe’ for the bladder?

Answer 17

• Lesions above the pontine micturition centre are ‘safe’ therefore the micturition remains to be coordinated
• Lesions below T12 are also safe, as the bladder and sphincter are flaccid as a result

Question 18

What lesions of the spinal cord would cause an ‘unsafe bladder’?

Answer 18

Lesions in between the pontine micturition centre and T12 are unsafe this is because the micturition process becomes uncoordinated and therefore high pressures in the resting bladder result which can cause urinary back flow and hydronephrosis