PHYS Micturition & Continence - Week 7

Question 1

What is the trigone? What is it composed of?

Answer 1

Triangular region of the bladder. Composed of smooth m.

Question 2

3 x histological layers of the bladder wall.

Answer 2

1. Stratified transitional epithelium – adapt to degree of distension & impermeable to water & salt (preventing reabsorption of toxic wastes and/or pathogens).
2. Lamina propria.
3. Smooth m = detrusor m.

Question 3

Significant of angle of entry of ureters into bladder.

Answer 3

Obliquely -> forms valve -> prevents backflow.

Question 4

What m controls the inner sphincter?

Answer 4

Detrusor m spiral around urethra to enable conscious control of continence.

Question 5

Which SYMP spinal nerves innervate what receptors on what muscle of the bladder?

Answer 5

T11-L2 roots. Synapse @ internal sphincter w a-adrenergic receptors.

Question 6

Which PARASYMP spinal nerves innervate what receptors on what muscle of the bladder?

Answer 6

S2-4 roots. Synapse @ detrusor m w cholinergic receptors.

Question 7

What nerve innervates pelvic floor musculature to control external sphincter of bladder?

Answer 7

Somatic pudendal nerve.

Question 8

Steps of the micturition reflex.

Answer 8

a. Bladder >400ml
b. Stretch receptors within bladder walls stimulated
c. Afferent sensory fibres from stretch receptors send impulses into SC
d. Motor neuron inhibited.
e. Both sphincters open
f. Contraction of detrusor.
g. Urine expelled.

Question 9

3 x causes of incontinence

Answer 9

1. Neurological interruption/neurogenic bladder
   a. Interruption of the peripheral afferent nerves from the bladder via de-affrentation -> atonic bladder (due to destruction of sensory nerve fibres & prevented transmission of stretch signals) -> bladder fills to capacity -> overflows a few drops at a time -> overflow incontinence -> bladder becomes distended, thin-walled & hypotonic.
   b. Interruption of both afferent & efferent nerves via denervation
   i. Upper Motor Neuron Spastic Neurogenic Bladder – hyper-reflexive bladder.
   ii. Lower Motor Neuron Flaccid Hypotonic Bladder – damage to peripheral nerves travelling from SC to bladder -> inability to empty.
   c. Interruption of the facilitatory and inhibitory pathways descending from the brain via SC transection (above S2)
2. Stress
   a. Damage to pelvic support structures
   b. Neurogenic urethral sphincter control.
3. Urge – uninhibited contraction of the bladder detrusor m.

Question 10

Urge incontinence is often associated w what syndrome?

Answer 10

Overactive bladder syndrome.

Question 11

Potential causes of stress incontinence.

Answer 11

Pregnancy, aging, obesity, radiation exposure.

Question 12

What law explains pressure & wall tension relationship in the bladder?

Answer 12

Laplace’s law - provides that pressure is slight until bladder is relatively full (i.e., >400ml urine).