Equations of Renal Function Flashcards
Glomerular Filtration Rate (GFR)
amount of plasma filtered per unit time
usually 100-125 mL/min
Filtration Fraction
GFR/RPF
RPF=Renal Plasma Flow
usually 15-20% of entering plasma is filtered
Renal Blood Flow(RBF) Formula
RPF/(1-HCT)
HCT=hematocrit
Clearance
explains the ability of the kidney to excrete a substance, based on its plasma concentration
dimensions of volume and time in mL/min
Clearance Formula
C=(UxV)/Px
mL/min
Excretion rate
UxV
mg/min
Ux
urinary concentration
mg/mL
V
urine flow rate
mL/min
Px
plasma concentration
mg/mL
Inulin
freely filtered(does not alter GFR), not absorbed, not secreted, not metabolized, clearance of inulin measures GFR, must be infused
amt filtered per minute = amount excreted per minute
Inulin formula
GFR = Clearance
GFR=(UinV)/Pin
Creatinine
used to measure GFR, does not need to be infused, easily filtered with some secretion,
breakdown product of muscle metabolism
Another clearance forumla
(GFRPx-reabsorbtion or +secretion)/Px
GFR formula
(Urine conc. of inulin or creat)x(urine volume/collection time)/Px
Tm
tubular transport maximum of glucose
375 mg/min
Glucose Level less than 375 mg/min(Tm)
glucose is reabsorbed, clearance is 0
Glucose level at or above 375 mg/min(Tm)
excess glucose appears in urine
Splay
threshold point is not absolute for all nephrons, rounding of curve
Glucose Clearance Formula
((GFRxPx)-Tm)/Px
Tm = 375 mg/min
if value obtained is 0 or negative then renal clearance is 0
PAH
clearance>GFR, more PAH appears in urine than is filtered due to Secretion,
Tm for secretion is 80 mg/min,
PAH concentration greater than 80mg/min(Tm)
some PAH remains in the peritubular capillaries
PAH concentration lower than 80mg/min(Tm)
all PAH is cleared
PAH clearance formula
((GFRxPx)+Tm)/Px
Tm = 80 mg/min
Sodium Glucose Transporter 2 inhibitors (SGLT2)
blocks renal PCT reabsorbtion of glucose, type 2 diabetes treatment, lowers Blood Sugar, lowers hemaglobin A1C
pee away filtered glucose instread of reabsorbing it.
