Question

question 28
substance x has a concentration of 15 meq/l in plasma and 15 meq/l in glomerular filtrate, and 5 meq/l in urine. what can be said about substance x?
a it is reabsorbed
b it is not freely filtered
c it is neither reabsorbed, nor secreted
d it is secreted

Explanation:

• If a substance is freely filtered (same concentration in plasma and glomerular filtrate as here, 15 mEq/L for both), and its concentration in urine (5 mEq/L) is less than in filtrate, it means some of the substance has been re - absorbed back into the bloodstream.
• Secretion would increase the amount in urine compared to filtrate. If it was neither reabsorbed nor secreted, the concentration in urine would be same as in filtrate (assuming no water re - absorption effect on concentration for simplicity here, but even with water re - absorption, reabsorption of the substance would still cause a decrease in its urine concentration relative to filtrate). And since concentration in plasma and filtrate is same, it is freely filtered.

Answer:

A. It is reabsorbed