Question

The following data were obtained from Bart:

24-hour Urine Sample

Total volume                                    1440 mL

Sodium concentration                      120 mEq/L

Potassium concentration                  100 mEq/L

Creatinine concentration                  200 mg/100 mL

GFR 200 mL/min

Urea concentration                           2050 mg/100 mL

Plasma Sample taken at the mid-point during the Urine collection

Sodium concentration                      140 mEq/L

Potassium concentration                  5 mEq/L

Creatinine concentration                  1 mg/100 mL

Urea concentration                           25 mg/100 mL

What fraction of Bart's filtered urea was filtered according to the above data?

a)

0.2

b)

1.0

c)

0.04

d)

0.41

e)

0.1

Answer 1

Urine volume = 1440 ml

Urea concentration in urine = 2050 mg /100ml

So, the amount of urea filtered = 2050 * 1440 / 100 = 29520mg

Urea concentration in plasma = 25mg/ 100ml

We know, the total average volume of blood in our body is 5L or 5000ml

So, amount of urea present in plasma = 25 * 5000/100 = 1250 mg

So total amount of urea = 29520 + 1250 = 30770mg

So the fraction of Brat's filtered urea filtered = 29520/30770 = 0.959

The fraction of unfiltered urea = 1250/30770 = 0.04