Micturition

Question 1

Type of muscle of the bladder

Answer 1

Smooth muscle (detrusor muscle)

Question 2

Type of epithelial lining

Answer 2

Transitional epithelium

Question 3

Shape of pressure-volume curve of bladder

Answer 3

Long flat segment as the initial increments of urine enter the bladder 》a sudden sharp rise as the micturition reflex is triggered.

Question 4

Normal daily urine production

Answer 4

750ml-2500mls

Question 5

What volume of urine gives one the first urge to void

Answer 5

100ml

Question 6

What volume of urine gives one the urgent urge to void

Answer 6

> 450ml

Question 7

Parasympatheitc, sympathetic and somatic motor innervation of bladder

Answer 7

Parasympatheitc = pelvic nerves S2-S4
Sympathetic = hypogastric nerves L1-L3
Somatic = Pudenal nerves S2-4

Question 8

Action of Parasympathetic innervation of bladder

Answer 8

Increases contraction of detrusor muscle 》pressure inside bladder
P = piss

Question 9

Action of Sympathetic innervation of bladder

Answer 9

Inhibit bladder contraction
Close internal “sphincter”
Main function is to prevent reflux of semen into bladder during ejaculation
S = semen

Question 10

Result of cutting hypogastric nerves

Answer 10

Increased frequency of micturition

Question 11

Action of Somatic innervation for bladder

Answer 11

Innervates skeletal muscle that forms the external urethral sphincter
Can keep sphincter closed even under strong bladder contractions

Question 12

What’s responsible for the sensory innervation of bladder

Answer 12

Stretch receptors in the bladder wall

Question 13

Action of stretch receptors

Answer 13

Bladder fills 》increased discharge of afferent nerves to spinal cord 》excitation of parasympathetic and inhibition of sympathetic outflow 》inhibition of somatic motoneurones 》pathways to sensory cortex => sensation of fullness

Question 14

What is micturition essentially

Answer 14

A spinal reflex, that may or may not be influenced by higher centres

Question 15

Volume of urine needed to initiate spinal reflex

Answer 15

~300-350mls

Question 16

How is delay achieved and what parts of the body are involved in it

Answer 16

By descending pathways from many brain centres, including cortex and brainstem
They inhibit parasympatheitc and stimulate somatic nerves of external sphincter

Question 17

How is voluntary micturition achieved and what is involved in it

Answer 17

Achieved by descending pathways

Which stimulate parasympathetic and inhibit somatic innervation of external sphincter

Question 18

After urination how is urine expelled from the urethra in males and females

Answer 18

Females = by gravity 
Males = contraction of the Bulbocavernosus muscle

Question 19

3 types of micturition abnormalities due to neural lesions and their effect

Answer 19

Interruption of afferent nerves
Interruption of both afferent and efferent nerves
Interruption of facilitatory and inhibitory descending pathways from the brain.

Bladder contracts but the contractions are insufficient to empty bladder completely 》urine is left in the bladder

Question 20

How do some paraplegic initiate voluntary voiding and how does this work

Answer 20

Stroke or pinch their thigh 》mild mass reflex
After spinal section, afferent stimuli irradiate from one reflex centre to another.
When a minor noxious stimulus is applied to the skin it may irradiate to autonomic centres, evoking voiding.