Use of clearance methods to quantify kidney function Flashcards
definition
The amount of plasma of a substance
cleared through the kidneys
for one minute
expressed in ml/min
function
measures the rate at which substances are removed from the body by the kidneys
FORMULA
C = renal clearance
V = urine output
U = concentration of substance of urine
P = concentration of substance in plasma
C = renal clearance
units
ml/min
V = urine output
units
ml/min
U = concentration of substance of urine
P = concentration of substance in plasma
UNITS
mmol/l
mg/ml
glomerular filtration (GF)
uses clearance of inulin/ creatinine
filtered amount = excreted amount
NO REABSORPTION
RENAL PLASMA FLOW (RPF)
uses the clearance of para-amino-hippuric acid
the amount of plasma passing through renal cortex per unit time
RPF = CPAH x 100 / 91
RENAL BLOOD FLOW (RBF)
normal range is 1200-1300ml/ min or 20-25% CO
RBF = RPF / ( 1- Hc)
Use of clearance methods to quantify kidney function - urea
clearance of inulin > clearance of urea
- because after being filtered, the urea is still reabsorbed back into the intersititum
Use of clearance methods to quantify kidney function - sodium
clearance of sodium is low
- after filtration almost 99% of na+ is reabsorbed along tubular system of nephron
Use of clearance methods to quantify kidney function
AMOUNT OF FILTERED SUBSTANCE
F = P x GFR
P = conc of substances in plasma
GF = ml/min
Use of clearance methods to quantify kidney function
AMOUNT OF EXCRETED SUBSTANCE
E = U x V
Use of clearance methods to quantify kidney function
AMOUNT OF REABSORBED SUBSTANCE
R = F - E
units = mmol/ min
Use of clearance methods to quantify kidney function
PERCENTAGE OF ABSORBED SUBSTANCE
%R(substance) = R(substance) / F(substance) x 100
