Question

Given that GFR is 125 mL/min and the clearance of substance Y is 200 mL/min, which of the following MUST be true of the renal handling of substance Y?

1) Y is freely filterable.
2) Y is reabsorbed.
3) Y is secreted.
4) Y is neither reabsorbed nor secreted.
5) Y is not freely filtered.

Answer 1

Since the clearance of substance Y (200 mL/min) is higher than the GFR (125 mL/min), it indicates that Y is being secreted in the kidney tubules.

Step-by-step explanation:

Given that the glomerular filtration rate (GFR) is 125 mL/min and the clearance of substance Y is 200 mL/min, it must be true that substance Y is secreted. The renal handling of substances involves filtration, reabsorption, and secretion. Since the clearance of substance Y is higher than the GFR, this indicates that additional Y must be entering the urine post-filtration. The only way this could happen is if substance Y is actively secreted into the tubule after it has been filtered. Therefore, option 3) Y is secreted, must be true.

it indicates that substance Y is being secreted by the kidneys. In this case, since the clearance of substance Y is 200 mL/min and the GFR is 125 mL/min, it follows that option 3) Y is secreted MUST be true of the renal handling of substance Y.