Correct Matched Pairs in Renal Physiology

Which of the following pairs is/are correctly matched?

Correct Answer: All the above

All three pairs are correctly matched:

Explanation of Each Pair

• Countercurrent multiplier → Loop of Henle: The Loop of Henle (particularly in juxtamedullary nephrons) acts as a countercurrent multiplier. The descending limb (permeable to water but not solutes) and the ascending limb (permeable to solutes but not water) work together to create a progressively increasing osmotic gradient in the renal medulla (from ~300 mOsm at cortex to ~1200 mOsm at papilla). This gradient is essential for concentrating urine.
• Countercurrent exchanger → Vasa recta: The Vasa recta (peritubular capillaries of juxtamedullary nephrons) act as a countercurrent exchanger. They passively exchange solutes and water with the medullary interstitium, preserving the osmotic gradient created by the Loop of Henle without washing it away.
• Yellow colour of urine → Urobilin: The characteristic yellow colour of urine is due to urobilin, an oxidized form of urobilinogen. Urobilinogen is produced by gut bacteria from bilirubin (a breakdown product of hemoglobin). Urobilinogen is reabsorbed, circulates in blood, and is excreted in urine where it oxidizes to urobilin.