What is the net urea reabsorption rate?: (A) 0 mg/min, (B) 25 mg/min, (C) 50 mg/min, (D) 75 mg/min
Answer is D. The net urea reabsorption rate is equal to the ﬁltered load of urea (GFR  x plasma urea concentration ) - urinary excretion rate of urea (urine urea concentration  x  urine ﬂow rate ). ​
Therefore, net urea reabsorption = (50 mL/min x 2.5 mg/mL) – (50 mg/mL x 1 mL/min) = 75 mg/min.