Micturition

Question 1

What is the gold standard (non-clinical) for measuring GFR? Why?

Answer 1

Inulin clearance

Because inulin is not reabsorbed so whatever is filtered will be excreted.

Question 2

What is the “normal” GFR?

Answer 2

125ml/min

Question 3

How quickly does GFR decrease?

Answer 3

1ml/min/ year after 30

Question 4

What is routinely used in order to estimate GFR?

Answer 4

Creatinine clearance

Question 5

Why can creatinine clearance not be the best measure of GFR?

Answer 5

Not a linear relationship btw GFR & creatinine (cannot detect small changes)

Question 6

What factors affect serum creatinine?

Answer 6

Muscle mass
Dietary intake (vegetarians & supplements)
Drugs

Question 7

What will glucose have a clearance of? Why?

Answer 7

0

Because all reabsorbed

Question 8

What is clearance of urea?

Answer 8

Less than inulin because some urea is reabsorbed

Question 9

What is used to measure renal plasma flow? (RPF)

Answer 9

PAH (paraaminohippuric acid)

Question 10

What is the normal renal plasma flow?

Answer 10

660mls/min

Question 11

What will be the clearance of penicillin compared to inulin?

Answer 11

Higher as it is filtered & secreted

Question 12

How does urine flow through ureters to bladder?

Answer 12

Smooth muscle peristaltic contractions

Question 13

What are the different ways muscles are arranged in the bladder?

Answer 13

Longitudinal
Circular
Spiral

Question 14

What type of muscle is detrusor muscle?

Answer 14

Smooth muscle

Question 15

What is a false sphincter?

Answer 15

Internal urethral sphincter acts as a spinster when smooth muscle relaxed

Question 16

What is a true sphincter?

Answer 16

External urethral sphincter - under voluntary control

Question 17

Where does the bladder lie posterior to?

Answer 17

Pbic symphysis

Question 18

What epithelium is the bladder composed of?

Answer 18

Transitional epithelium

Question 19

Where do the ureters open into?

Answer 19

Trigone of bladder

Question 20

What are the openings called where the ureters enter the bladder?

Answer 20

Vesicoureteric openings

Question 21

As volume in the bladder increases what happens to pressure?

Answer 21

Increased intravesical pressure

Question 22

Which nerves are responsible for contraction of detrusor muscle?

Answer 22

S2-4 parasympathetic

Question 23

Which nerves inhibit smooth muscle contraction at bladder?

Answer 23

Sympathetic (hypogastric) nerves

Question 24

What is the main function of sympathetic innervation at the bladder?

Answer 24

Urethral contraction to prevent semen moving into bladder on ejaculation

Question 25

Which nerves innervate the skeletal muscle of the external urethral sphincter keeping it closed?

Answer 25

Pudental nerves (S2-4)

Question 26

As sensory afferents increase firing from bladder with increased stretch what do interneurons do?

Answer 26

Increase parasympathetic outflow Decrease sympathetic outflow Inhibition of motorneurones to external sphincter Pathways to sensory cortex

Question 27

What can the micturition reflex be compared to?

Answer 27

Spinal reflex

Question 28

At what volume will the bladder initiate micturition reflex?

Answer 28

300-350mls

Question 29

How can we delay micturition from reflex voiding?

Answer 29

Delayed by descending pathways which inhibit parasympathetic outflow

Question 30

In voluntary initiation of voiding, what will be observed?

Answer 30

Descending pathways will stimulate parasympathetic outflow & inhibit somatic motto neurones to external sphincter

Question 31

What other muscles are involved in continence?

Answer 31

Pelvic floor muscles

Question 32

What are the 3 major types of neuronal lesion which lead to micturition abnormalities?

Answer 32

Afferent nerve interruption Interruption of both afferent & efferent Interruption of facilitatory & inhibitory descending pathways

Question 33

Ux is short for?

Answer 33

Urine concentration

Question 34

V is short for?

Answer 34

Urine flow rate

Question 35

Px is short for?

Answer 35

Plasma concentration

Question 36

What is the equation which defines GFR?

Answer 36

Plasma clearance (C) = Ux V/Px

Question 37

How much urine should be produced / day?

Answer 37

750-2500mls