Question

Countercurrent multiplier in kidney

• A. Vasa recta
• B. Loop of Henle
• C. PCT
• D. DCT

Hint:

- Multiplier = Loop of Henle (active transport, creates the concentration gradient).
- Exchanger = Vasa Recta (passive diffusion, maintains/preserves the gradient).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The kidney concentrates urine through a countercurrent mechanism, creating an osmotic gradient in the renal medullary interstitium.

Step 3: Detailed Explanation:
The countercurrent system of the kidney consists of two distinct components:
1. Countercurrent Multiplier (Loop of Henle): The descending limb is highly permeable to water but impermeable to solutes, whereas the ascending limb actively pumps out NaCl into the medullary interstitium and is impermeable to water. This arrangement multiplies the osmotic gradient.
2. Countercurrent Exchanger (Vasa recta): These specialized medullary capillaries passively exchange solutes and water to sustain the medullary concentration gradient without washing it out.
PCT (Proximal Convoluted Tubules) and DCT (Distal Convoluted Tubules) are involved in solute reabsorption and acid-base regulation, but do not act as countercurrent multipliers.

Step 4: Final Answer
The anatomical structure that acts as the countercurrent multiplier is the Loop of Henle.