Micturition Flashcards
What is the gold standard (non-clinical) for measuring GFR? Why?
Inulin clearance
Because inulin is not reabsorbed so whatever is filtered will be excreted.
What is the “normal” GFR?
125ml/min
How quickly does GFR decrease?
1ml/min/ year after 30
What is routinely used in order to estimate GFR?
Creatinine clearance
Why can creatinine clearance not be the best measure of GFR?
Not a linear relationship btw GFR & creatinine (cannot detect small changes)
What factors affect serum creatinine?
Muscle mass
Dietary intake (vegetarians & supplements)
Drugs
What will glucose have a clearance of? Why?
0
Because all reabsorbed
What is clearance of urea?
Less than inulin because some urea is reabsorbed
What is used to measure renal plasma flow? (RPF)
PAH (paraaminohippuric acid)
What is the normal renal plasma flow?
660mls/min
What will be the clearance of penicillin compared to inulin?
Higher as it is filtered & secreted
How does urine flow through ureters to bladder?
Smooth muscle peristaltic contractions
What are the different ways muscles are arranged in the bladder?
Longitudinal
Circular
Spiral
What type of muscle is detrusor muscle?
Smooth muscle
What is a false sphincter?
Internal urethral sphincter acts as a spinster when smooth muscle relaxed
What is a true sphincter?
External urethral sphincter - under voluntary control
Where does the bladder lie posterior to?
Pbic symphysis
What epithelium is the bladder composed of?
Transitional epithelium
Where do the ureters open into?
Trigone of bladder
What are the openings called where the ureters enter the bladder?
Vesicoureteric openings
As volume in the bladder increases what happens to pressure?
Increased intravesical pressure
Which nerves are responsible for contraction of detrusor muscle?
S2-4 parasympathetic
Which nerves inhibit smooth muscle contraction at bladder?
Sympathetic (hypogastric) nerves
What is the main function of sympathetic innervation at the bladder?
Urethral contraction to prevent semen moving into bladder on ejaculation
Which nerves innervate the skeletal muscle of the external urethral sphincter keeping it closed?
Pudental nerves (S2-4)
As sensory afferents increase firing from bladder with increased stretch what do interneurons do?
Increase parasympathetic outflow
Decrease sympathetic outflow
Inhibition of motorneurones to external sphincter
Pathways to sensory cortex
What can the micturition reflex be compared to?
Spinal reflex
At what volume will the bladder initiate micturition reflex?
300-350mls
How can we delay micturition from reflex voiding?
Delayed by descending pathways which inhibit parasympathetic outflow
In voluntary initiation of voiding, what will be observed?
Descending pathways will stimulate parasympathetic outflow & inhibit somatic motto neurones to external sphincter
What other muscles are involved in continence?
Pelvic floor muscles
What are the 3 major types of neuronal lesion which lead to micturition abnormalities?
Afferent nerve interruption
Interruption of both afferent & efferent
Interruption of facilitatory & inhibitory descending pathways
Ux is short for?
Urine concentration
V is short for?
Urine flow rate
Px is short for?
Plasma concentration
What is the equation which defines GFR?
Plasma clearance (C) = Ux V/Px
How much urine should be produced / day?
750-2500mls
