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MBBS QUESTION #10259
Question 1
Renal plasma flow can be estimated using the clearance of para-aminohippuric acid (PAH), which is considered nearly completely removed from plasma in a single pass through the kidney because PAH is:
  • Freely filtered at the glomerulus and additionally actively secreted by the proximal tubule, so essentially all of it is cleared from renal plasma in one pass✔️
  • Neither filtered nor secreted by the nephron
  • Completely reabsorbed by the distal tubule
  • Only filtered, with no tubular secretion at all
Correct Answer Explanation
Because PAH is both filtered and vigorously secreted by proximal tubular cells, nearly 90% of the PAH delivered to the kidney is cleared in a single pass, allowing its clearance to approximate effective renal plasma flow — distinct from inulin, which measures GFR only.