physiology of micturition Flashcards
what are the functions of the urinary tract?
to collect urine produced by the kidneys
to store collected urine safely
to expel urine when socially acceptable
where abouts are the kidneys in relation to the vertebral levels?
T11-L3
Which blood vessel supplies the kidneys and what is this a branch of?
renal artery - branch of the abdominal aorta at L1
are the kidneys are ureters retroperitoneal or intraperitoneal?
retroperitoneal
At what point do the ureters cross the iliac vessels?
at the pelvic brim
what are the areas of narrowing of the ureters
Pelviuteric junction/ uteropelvic junction
pelvic brim
insertion into the trigon of the bladder
how is reflux of the urine prevented?
valvular mechanism at the vesicoureteric junction
what is the name of the muscle that makes up the whole of the bladder wall?
detrusor
what structures for the trigone of the bladder?
the ureters and the urethra
describe the innervation of the baldder
- parasympathetic nerve = pelvic nerve from S2-4
- sympathetic nerve = hypogastric plexus from T11-L2
- somatic nerve = pudendal nerve S2-4
- sensory afferent pelvic nerve sends signals from the detrusor to the sacral spinal cord
What are the four neural control centres for the bladder?
- cortex: voluntary control
- pontine micturition centre/periaqueductal grey: coordinates detrusor contraction and urethral relaxation ie coordinates guarding
- sacral micturition centre in S2-4
- Onuf’s nucleus in the sacral micturition centre involved in the guarding reflex
in what stage of the micturition cycle does the bladder spend most of its time in?
storage phase
when it is inappropriate to void, what reflex is used?
guarding reflex
when it is appropriate to void, which reflex occurs?
micturition reflex
When is the first sensation of micturition and can this be overridden?
at 100-200 mls
can be overridden
what is the normal adult bladder capacity?
400-500 mls
what is the term for the volume of the bladder increasing but the pressure inside the bladder remaining low?
receptive relaxation
What property of the detrusor muscle allows it to carry out receptive relaxation?
it is a very compliant muscle
Describe what happens in the filling phase of the baldder
- at low volumes of bladder contents, the afferent pelvic nerve sends SLOW firing signals to the pontine micturition centre via the sacral micturition centre
- the sympathetic nerve stimulation (hypogastric plexus) maintains detrusor muscle relaxation
- the somatic (pudendal nerve) stimulation maintains urethral contraction
explain the steps of the micturition reflex
- Higher volumes stimulate the afferent pelvic nerve to send FAST signals to the sacral micturition centre in the sacral spinal cord
- Pelvic parasympathetic nerve is stimulated and the detrusor muscle contracts
- Pudendal nerve is inhibited and the external sphincter relaxes
What is the guarding reflex?
voluntary control of micturition - prevents micturition when it is not socially acceptable to do so
Explain the guarding reflex
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
what does the pudendal nerve (somatic) control?
the external urethral sphincter - under voluntary control by this somatic nerve
what does the parasympathetic and sympathetic system control?
the detrusor muscle
