Question

what substance found, in high concentration, in the renal medulla helps increase the amount of water drawn out of the tubule to be picked up by the blood?
a glucose
b amino acids
c urea
d chloride ions

Explanation:

To solve this, we analyze each option:

• Option A: Glucose is reabsorbed earlier in the nephron (proximal tubule) and not a major osmolyte in the renal medulla for water reabsorption.
• Option B: Amino acids are also reabsorbed in the proximal tubule and not a key substance for medullary osmolarity.
• Option C: Urea is concentrated in the renal medulla and contributes to the osmotic gradient that draws water out of the tubule (collecting duct) into the blood. This is part of the counter - current mechanism in the kidney.
• Option D: Chloride ions are important in the nephron but not the main substance in the renal medulla for this specific water - drawing mechanism.

Answer:

C. Urea