Micturition

Question 1

What is micturition?

Answer 1

The act of urination (emptying the bladder)

Question 2

Basic process

Answer 2

Urine made in kidneys (1 ml.min-1)
Urine stored in the bladder
Urine released from bladder

Question 3

Kidney to bladder

Answer 3

Urine from al collecting ducts of al nephrons
Emptying into the renal pelvis
Urine enters ureter

Question 4

Peristaltic waves

Answer 4

~1-6 contractions/min

Question 5

What is the pressure in the ureters

Answer 5

10-20 mmHg

Question 6

What control are ureters under?

Answer 6

Myogenic in origin not under CNS

Question 7

Kidney stones

Answer 7

Crystals that separate from the urine within the urinary tract
Normal urine contains citrate to prevent this

Question 8

What is present in most kidney stones?

Answer 8

Calcium (80%) as calcium oxalate or less often as calcium phosphate.
Then uric acid (<10%)
Struvite (<10%)
Cystine (<5%)

Question 9

What causes kidney stones?

Answer 9

Poor urine output/ obstruction, altered urinary pH, infections, excess dietary intake, low concentration of inhibitors

Question 10

Whos is more likely to have kidney stones

Answer 10

Men due to testosterone

Question 11

Symptoms of kidney stones

Answer 11

Dysuria (painful urination)

Question 12

How much can the bladder store?

Answer 12

400 ml w/o much increase in pressure - spherical structure

Question 13

Female bladder

Answer 13

Short urethra - only carries urine

External sphincter poorly developed - more prone to incontinence particularly after childbirth

Question 14

Male bladder

Answer 14

Carries urine and semen

Urine elimination aided by contraction of bulbocavernosus muscle in the penis

Question 15

Summary of bladder

Answer 15

Lining - transitional epithelium
Bladder muscle - detrusor
Impermeable to salt & water
Permeable to lipophilic molecules

Question 16

Internal sphincter

Answer 16

Smooth muscle, involuntary control

Question 17

External sphincter

Answer 17

Striated muscle, voluntary control

Question 18

Bladder innervation 1

Answer 18

Neural circuits in brain & SC coordinate activity of bladder & sphincters circuits act as an on-off switch to alternate between storage & elimination

Question 19

Bladder innervation 2

Answer 19

3 peripheral nerves

• Parasympathetic (pelvic nerve)
• Sympathetic (hypogastric nerves)
• The somatic nervous system (pudendal nerve)

Question 20

Bladder innervation 3

Answer 20

• Sensory: gives sensation (awareness) of fullness and also pain from disease
• Motor: causes contraction and relaxation of the detrusor muscle and external sphincter to control micturition

Question 21

What do ACh and ATP do the Detrusor

Answer 21

Causes detrusor to contract

Question 22

What does NA do the detrusor

Answer 22

Inhibits transmission at parasympathetic ganglia - indirectly causes detrusor to relax
Also directly via B-Rs (also in trigone area) causes detrusor to relax

Question 23

What does NO and ACh do the internal sphincter?

Answer 23

Relaxes

Question 24

What does Noradrenaline (NA) do to the internal sphincter?

Answer 24

Contracts

Question 25

What does the ACh to the internal sphincter?

Answer 25

Tonic activity holds external sphincter closed

Question 26

Parasympathetic neurons

Answer 26

Contract detrusor - via ACh (muscarinic) + ATP (Purigenic R) -Relax internal sphincter - via NO (cGMP) & ACh (nictotinic) Encourage micturition

Question 27

Sympathetic neurons

Answer 27

RELAX detrusor- Indirectly via NA (a-R) & directly via NA (beta receptors) CONTRACTS internal sphincter - NA (alpha R) Inhibits Micturition

Question 28

Somatic neuron

Answer 28

Contract external sphincter - ACh (nicotinic R) | Inhibit micturition

Question 29

Afferent innervation

Answer 29

The main afferent pathway is via pelvic nerve (parasympathetic): Small myelinated A/delta fibers - micturition reflex Stretch receptor - signal wall tension Volume receptors - signal bladder filling

Question 30

A fibres

Answer 30

Sense tension in detrusor Filling of bladder Detrusor contraction BLADDER FULLNESS, discomfort

Question 31

C fibres

Answer 31

Respond to damage & inflammatory mediators | Unmeylinated C fibres - endings in/near epithelium

Question 32

What happens when the bladder is empty?

Answer 32

Sphincters closed | Bladder pressure is low

Question 33

What happens when urine arrives?

Answer 33

Detrusor relaxes progressively Little increase in pressure Sphincters still closed

Question 34

How is micturition modified?

Answer 34

Voluntary controlled The act is an autonomic reflex However, is inhibited by higher centers in the brain

Question 35

What do disease and injury do to the nervous system?

Answer 35

Disrupts voluntary control of micturition - Bladder hyperactivity & urge incontinence - Stress incontinence

Question 36

Retained urine

Answer 36

Clinical infection UTI

Question 37

Bladder infection

Answer 37

Called Cystitis or a bladder infection

Question 38

Kidney infection

Answer 38

One or both kidney - called pyelonephritis

Question 39

Ureter infection

Answer 39

Rarely the site of infection

Question 40

Urethra infection

Answer 40

Urethritis

Question 41

How is micturition aided?

Answer 41

Reflex contraction of peri-urethral striated muscles also helps compress the urethra

Question 42

How can higher centers modify micturition?

Answer 42

Contract external sphincter & levator muscle consiously

Question 43

What are some risk factors of UTIs

Answer 43

``` Diabetes Long term catheter Pregnancy Prolonged immobility Kidney stones Bowel incontinence Older age ```

Question 44

Problems with an ageing bladder

Answer 44

Slow urine stream - lead to incomplete emptying and an infection Incontinence

Question 45

Treatment for ageing bladder

Answer 45

Surgery - bladder neck suspension | Bo