Question

What creates the osmotic gradient in the renal medulla?

1) active transport of solute out of the proximal tubule
2) special transport systems of the loops of Henle of juxtamedullary nephrons
3) special transport systems of the loops of Henle of cortical nephrons
4) active transport of solute out of the distal tubules and collecting ducts
5) passive transport of solute out of the distal tubules and collecting ducts

Answer 1

The osmotic gradient in the renal medulla is created by the juxtamedullary nephrons' loops of Henle, functioning as a countercurrent multiplier system.

Step-by-step explanation:

The osmotic gradient in the renal medulla is primarily created by the special transport systems of the loops of Henle of juxtamedullary nephrons. As the filtrate moves through the descending limb of the loop of Henle, it becomes increasingly concentrated due to the absorption of water. Then, in the ascending limb, active transport of Na+ and Cl- ions out of the filtrate into the renal medulla contributes to the high osmotic gradient. This process is known as the countercurrent multiplier system, which is pivotal for urine concentration.