Final answer:
The vasa recta in the medulla acts as a countercurrent exchanger, preserving the osmotic gradient by slowly exchanging water and solutes with the loop of Henle, crucial for the kidney’s ability to concentrate urine and conserve water. The correct option is 1. vasa recta
Step-by-step explanation:
The vasa recta within the medulla acts as a countercurrent exchanger. In the loop of Henle, the descending and ascending limbs have different permeabilities, which creates an osmotic gradient in the renal medulla. This gradient is crucial for concentrating urine and conserving water.
The role of the vasa recta is to preserve this gradient by slowly exchanging water and solutes with the loop of Henle, working in conjunction with the loop’s countercurrent multiplier system.
As the blood flows down the vasa recta, it gains Na+ and urea while losing water; when the blood flows back up, it loses Na+ and urea and gains water, thus maintaining the osmolarity necessary for the kidney to function efficiently. The correct option is 1. vasa recta