Renal Physiology Equations- tables 6.3 & 6.4

Renal clearance formula

([U]x × V) / [P]x

Clearance ratio formula

Cx / Cinulin

Renal plasma flow (RPF) formula

([U]PAH × V) / ([RA]PAH - [RV]PAH)

Effective renal plasma flow formula

([U]PAH × V) / [P]PAH

Renal blood flow equation

RPF / (1 - Hematocrit)

Glomerular filtration rate equation

([U]inulin × V) / [P]inulin

Filtration fraction formula

GFR / RPF

Filtered load formula

GFR × [P]x

Excretion rate formula

V × [U]x

Reabsorption or secretion rate formula

Filtered load - Excretion

Free-water clearance (CH2O) formula

V - C osm

Why is inulin used as a reference substance to measure GFR?

It is freely filtered, but neither reabsorbed nor secreted.

Significance of Cx / Cinulin < 1.0

Net reabsorption of substance x has occurred.

Significance of Cx / Cinulin > 1.0

Net secretion of substance x has occurred.

C

clearnace

[U]

concentration in urine

[P]

concentration in plasma

V

urine flow rate

GFR

glomerular filtration rate

RPF

renal plasma flow

RBF

renal blood flow

[TF]

concentration in tubular fluid

[TF/P]x

concentration of x in tubular fluid relative to concentration of x in plasma

[TF/P]inulin

concentration of inulin in tubular fluid relative to concentration of inulin in plasma

[TF/P]x / [TF/P]inulin

fraction of the filtered load remaining in tubular fluid or fractional excretion