7-Micturition

Question 1

Describe the overall process of micturition

Answer 1

Urine made in kidney 
Urine stored in bladder
Sphincter muscles relax
Detrusor contracts 
Bladder empties via urethra

Question 2

What are the functions of nervous control in the bladder?

Answer 2

Provide sensations of bladder filling and pain
Allow bladder to relax to accommodate increased volume of urine
Initiate and maintain voiding so bladder has minimal residual volume
Integrated regulation of smooth muscle and skeletal muscles of sphincters of urethra

Question 3

Describe phase 1 of micturition

Answer 3

Filling phase - bladder relaxes to accommodate an increased volume of urine. Urethral sphincters increase tone to maintain continence

Question 4

Describe phase 2 of micturition

Answer 4

Voiding phase- urethral sphincters relax and bladder contracts, more so in men than women.

Question 5

What is the function of the prostatic urethra?

Answer 5

Prevents retrograde ejaculation into the bladder

Question 6

Describe the sympathetic control of phase 1

Answer 6

Nerve roots s2-s4 (keeps piss off the floor)
Innervates detrosal muscle at B3 receptors, inhibiting smooth muscle contraction.
Innervates internal urethral sphincter at a1 receptors, exciting it causing it to contract, allowing bladder to expand while maintaining continence

Question 7

Describe somatic motor control of phase 1

Answer 7

Nerve roots s2-s4 (keeps piss off the floor), runs along pudendal nerve.
Controlled by L centre in the pons
Innervates external urethral sphincter, excites it causing to close.
(EUS also contains skeletal muscle so partly voluntary control)

Question 8

What drugs affect phase 1?

Answer 8

A1 antagonists, relax IUS, used to treat men with lower UT symptoms who can’t urinate
B3 agonists acts on bladder, relaxes bladder increasing its capacity, used to treat overactive bladder

Question 9

Describe sensory innervation in phase 2

Answer 9

Sensory neurones syanpse with parasympathetic nerves that have their roots in s2-s4

Question 10

Describe parasympathetic innervation in phase 2

Answer 10

Nerve roots s2-s4
Innervates detrusor at M3 receptors, exciting it causing it to contract. Activates micturition centre in the pons, which sends inhibitory signals to L centre (and the sympathetic nerves it regulates) causing external sphincter to relax

Question 11

What drugs affect phase 2?

Answer 11

M3 antagonists, prevent bladder from contracting so allow for more urine retention

Question 12

Describe the pressure changes that occur during micturition

Answer 12

Phase 1 - pressure doesn’t increase proportional to volume increases, as bladder expands to hold more urine. Minor increases until threshold of ~500ml is reached, where pressure massively increases
Phase 2- Bladder contracts rhythmically as volume decreases, creating spikes in pressure.

Question 13

Describe micturition in babies

Answer 13

Have an uncontrollable reflex arc as the micturition pathways (in brain) have not been myelinated

Question 14

Describe the effect of a spinal cord injury above S2 on micturition

Answer 14

Micturition reflex becomes overactive due to loss of inhibition signals. Bladder fills to a small amount and then empties

Question 15

Describe the effect of a spinal cord injury at s2-s4

Answer 15

Lose sensory input and motor output to the bladder, so bladder will fill to capacity then dribble out (incontinence)