Biomedical Engineering: Bridging Medicine and Technology 1st Edition by Veronique Tran,Mark Saltzman

Exercise 6

PAH has the property of being actively secreted from the capillaries sur-
rounding the kidney tubules into these tubules (thus into the urine). At low
plasma PAH concentrations (up to 8 mg/100 mL), the fraction of PAH carried
by the blood to the kidneys, which is lost to the urine via both glomerular
filtration and secretion, totals 91%, as determined by sampling the blood
just proximal to the kidney (i.e., from the renal artery) and just distal to
the kidneys (i.e., from the renal vein). At higher concentrations, the fraction
extracted is lower. If the same procedure as in problem 7 (which described
using inulin to measure GFR) is carried out using PAH, the plasma concen-
tration is 1 mg/100 mL, and the urine collected over a 1-hour period contains 0.35 mg of PAH, what is the rate of plasma flow to the kidneys?