3.5. Regulation of Osmolarity - The Role of Urea

Question 1

What happens in the presence of ADH (Vasopressin)?

Answer 1

Movement of H2O out of the collecting duct, back into circulation (via the Vasa Recta)

Question 2

What happens to urea in the presence of ADH (Vasopressin)?

Answer 2

This becomes concentrated in the collecting ducts

Question 3

Are collecting duct membranes permeable to Urea?

Answer 3

Yes, relatively - particularyly near the medullary tips

Question 4

What is the result of the increased concentration of urea in the collecting ducts, and the collecting ducts permeability to urea?

Answer 4

These is an increasing tendency for urea to move out of the collection duct, down its concentration gradient.

Question 5

What happens to urea, in an Anti-Diuresis with high levels of ADH?

Answer 5

Urea will be reabsorbed and retained

Question 6

What is the purpose of retaining urea in Anti-Diuresis with high levels of ADH?

Answer 6

1. To save water

2. To reinforce the interstitial gradient in the ascending limbs in the loop of henle

Question 7

What would happen if urea was left in the tubule?

Answer 7

It would exert an osmotic effect to hold onto water (in the tubule), increasing the risk of dehydration