Question

By the time the filtrate reaches the loop of Henle, the reabsorption of water and ions has ________.

1) left the filtrate iso-osmotic
2) left the filtrate hyperosmotic
3) left the filtrate hypoosmotic
4) removed all of the potassium from the filtrate
5) removed all of the sodium from the filtrate

Answer 1

In the loop of Henle, the permeability of the membrane changes, and the loop acts as a countercurrent multiplier.

Step-by-step explanation:

In the loop of Henle, the permeability of the membrane changes. The descending limb is permeable to water, not solutes; the opposite is true for the ascending limb. Additionally, the loop of Henle invades the renal medulla, which is naturally high in salt concentration and tends to absorb water from the renal tubule and concentrate the filtrate. The osmotic gradient increases as it moves deeper into the medulla. Because two sides of the loop of Henle perform opposing functions, as illustrated in Figure 41.8, it acts as a countercurrent multiplier. The vasa recta around it acts as the countercurrent exchanger.