physiology of micturition

Question 1

what are the functions of the urinary tract?

Answer 1

to collect urine produced by the kidneys
to store collected urine safely
to expel urine when socially acceptable

Question 2

where abouts are the kidneys in relation to the vertebral levels?

Answer 2

T11-L3

Question 3

Which blood vessel supplies the kidneys and what is this a branch of?

Answer 3

renal artery - branch of the abdominal aorta at L1

Question 4

are the kidneys are ureters retroperitoneal or intraperitoneal?

Answer 4

retroperitoneal

Question 5

At what point do the ureters cross the iliac vessels?

Answer 5

at the pelvic brim

Question 6

what are the areas of narrowing of the ureters

Answer 6

Pelviuteric junction/ uteropelvic junction
pelvic brim
insertion into the trigon of the bladder

Question 7

how is reflux of the urine prevented?

Answer 7

valvular mechanism at the vesicoureteric junction

Question 8

what is the name of the muscle that makes up the whole of the bladder wall?

Answer 8

detrusor

Question 9

what structures for the trigone of the bladder?

Answer 9

the ureters and the urethra

Question 10

describe the innervation of the baldder

Answer 10

1. parasympathetic nerve = pelvic nerve from S2-4
2. sympathetic nerve = hypogastric plexus from T11-L2
3. somatic nerve = pudendal nerve S2-4
4. sensory afferent pelvic nerve sends signals from the detrusor to the sacral spinal cord

Question 11

What are the four neural control centres for the bladder?

Answer 11

1. cortex: voluntary control
2. pontine micturition centre/periaqueductal grey: coordinates detrusor contraction and urethral relaxation ie coordinates guarding
3. sacral micturition centre in S2-4
4. Onuf’s nucleus in the sacral micturition centre involved in the guarding reflex

Question 12

in what stage of the micturition cycle does the bladder spend most of its time in?

Answer 12

storage phase

Question 13

when it is inappropriate to void, what reflex is used?

Answer 13

guarding reflex

Question 14

when it is appropriate to void, which reflex occurs?

Answer 14

micturition reflex

Question 15

When is the first sensation of micturition and can this be overridden?

Answer 15

at 100-200 mls

can be overridden

Question 16

what is the normal adult bladder capacity?

Answer 16

400-500 mls

Question 17

what is the term for the volume of the bladder increasing but the pressure inside the bladder remaining low?

Answer 17

receptive relaxation

Question 18

What property of the detrusor muscle allows it to carry out receptive relaxation?

Answer 18

it is a very compliant muscle

Question 19

Describe what happens in the filling phase of the baldder

Answer 19

1. at low volumes of bladder contents, the afferent pelvic nerve sends SLOW firing signals to the pontine micturition centre via the sacral micturition centre
2. the sympathetic nerve stimulation (hypogastric plexus) maintains detrusor muscle relaxation
3. the somatic (pudendal nerve) stimulation maintains urethral contraction

Question 20

explain the steps of the micturition reflex

Answer 20

1. Higher volumes stimulate the afferent pelvic nerve to send FAST signals to the sacral micturition centre in the sacral spinal cord
2. Pelvic parasympathetic nerve is stimulated and the detrusor muscle contracts
3. Pudendal nerve is inhibited and the external sphincter relaxes

Question 21

What is the guarding reflex?

Answer 21

voluntary control of micturition - prevents micturition when it is not socially acceptable to do so

Question 22

Explain the guarding reflex

Answer 22

the afferent sensory pelvic nerve sends signals to the pontine micturition centre and this is transmitted to higher cortical centres

sympathetic (hypogastric) nerve stimulation results in detrusor relaxation

pudendal nerve (somatic) stimulation results in contraction of the external urethral sphincter

Question 23

what does the pudendal nerve (somatic) control?

Answer 23

the external urethral sphincter - under voluntary control by this somatic nerve

Question 24

what does the parasympathetic and sympathetic system control?

Answer 24

the detrusor muscle

Question 25

What reflex is used when a child is not potty trained?

Answer 25

sacral micturition reflex