renal assessment and micturition

Question 1

why is ability to measure GFR important

Answer 1

1. in patient w renal disease, progression of underlying disease process results in nephron destruction and dec nephron function - progression indicated by reduction in GFR
2. many drugs are removed from body by excretion by filtration. When GFR falls, excretion falls so may need to adjust dose appropriate to decreasing renal function

Question 2

total GFR

Answer 2

sum of all filtration by functioning nephrons

Question 3

measurement of GFR

Answer 3

plasma clearance tests are used to measure renal function. They measure ability of kidney to clear plasma of various substances

Question 4

gold standard plasma clearance test

Answer 4

insulin

loading IV dose of insulin, allow time to equilibriate, then sample simultaneousluy plasma and urine

Question 5

why is insulin a god measurement of GFT

Answer 5

insulin is freely filter at the glomerulus and neither reabsorbed nor secreted

it is not metabolised by the kidney and doesn’t interfere with normal renal function and so insulin clearance is measure of GFR

Question 6

normal GFR in man

Answer 6

125ml/min

Question 7

what is used in practice to measure GFR

Answer 7

not insulin - too cumbersome

51Cr-EDTA has been used instead - suitable radioactive subastance handled by kidney in same way insulin

Question 8

why is GFR now not measured prropery

Answer 8

too complex and expencive
takes several hours
requires injection of istope

Question 9

what is used routinely to estimate GFR

Answer 9

creatinine

creatinine is endogenous (breakdown produce of muscel creatine)
good agreement with insulin clearance

Question 10

factors affecting creatinine

Answer 10

muscle mass: athletes vs malnutrition
dietary intake: creatine supplements vs veggies
drugs: some lead to increses

Question 11

normal GFR

Answer 11

approx 100mls/min/1.73m2

across range of adults, sexes, kidney function and size

Question 12

glucose clearance

Answer 12

usually zero because all is normally reabsorbed

Question 13

clearance of urea

Answer 13

less than that of insulin because some urea is reabsorbed

Question 14

PAH clearance (organic anion para-amino-hippuric acid)

Answer 14

used to measure renal plasma flow (RPF)

Question 15

why is PAH clearance used to measure renal plasma flow

Answer 15

PAH is freely filtered at glomerulus and then PAH remaining in plasma is actively secreted into tubule so that >9-% of plasma is cleared of its PAH content in one transit of kidney

PAH clearance is a measure of all plasma flowing through kidneys in given time = renal plsma flow

Question 16

what is PAH clearance a measure of

Answer 16

all the plasma flowing through the kidneys in a given time = renal plasma flow

Question 17

normal renal plasma flow

Answer 17

~660mls/min

Question 18

penicillin clearance

Answer 18

greater clearance than insulin because filtered and secreted

Question 19

how does urine get to bladder

Answer 19

flows from kidneys to ureters via peristaltic contraction of the smooth muscles of the ureters
enter bladder at an oblique angle (prevent reflux of urine)

Question 20

bladder

Answer 20

bag of smooth muscle, arranged in spiral, longitudinal and circular bundles: detrusor muscle

contraction of this muscle is mainly responsible for empyting bladder during micturtition

Question 21

internal urethral sphincter

Answer 21

not a true sphincer

where the smooth muscle at start of urethra acts as a sphincter when smooth muscle is relaxed

Question 22

external urethral sphincter

Answer 22

true sphincter

made of skeletal muscle under voluntary somatic control

Question 23

where is bladder

Answer 23

lies in midline posterior to pubic bones

anterior to reproductive system and rectum

Question 24

lining of bladder

Answer 24

transitional epithelium

Question 25

trigone of bladder

Answer 25

2 vesicoureteric openings

urethral opening

Question 26

urethral obstructions cause

Answer 26

bilateral renal problems

Question 27

ureter obstruction causes

Answer 27

unilateral renal problems

Question 28

normal daily urine production

Answer 28

750-2500mls

Question 29

control of micturition: motor innervation

Answer 29

1. rich parasympathetic supply inc which cause contraction detrusor muscle - inc pressure in bladder
2. sparse sympathetic supply inhibit bladder contraction - main function to prevent reflux semen into bladder during ejaculation
3. somatic motoneurones (pudendal nerve) innervate skeletal muscle that forms external urethral sphincer,keeps it closed even against strong bladder contractions

Question 30

control of micturition: sensory innervation

Answer 30

stretch receptor afferent from bladder wall, as it fills inc discharge in afferents to spinal cord -
via interneurones;
1. exctitation parasympathetic
2. inhibition sympathetic
3. inhibition somatic motoneurones to external sphincter
4. pathways to sensory cortex - sensation of fullness

Question 31

in adults - volume of urine in bladder required to initiate spinal reflex

Answer 31

300-350mls

Question 32

how is delay in micturition accomplished

Answer 32

descending pathways from many brain centres which:

1. inhibit parasympathetic
2. stimulate somatic nerves to external sphincter, thus overiding input from bladder stretc receptors

Question 33

mechanism of voluntary micturition

Answer 33

descending pathways wich

1. stimulate parasympathetic
2. inhibit somatic motor neurones

Question 34

3 major types of micurition abnormaliies due to neural lesions

Answer 34

1. interuption of afferent nerves
2. interuption of both afferent and efferent nerves
3. interuption of facilitatory and inhibitory descending pathways frombrian

Question 35

all 3 types of micturition abnormalities result in

Answer 35

bladder contracts but contractions are generally insufficient to empty bladder completely and urine is left in bladder