Role of ADH (Vasopressin)

[Psa]

Destroyer states that this sentence is true:

"In the absence of vasopressin, the walls of the collecting duct are practically impermeable to water"

But the solution states:

"If you did not have ADH (vasopressin) you would lose H2O, large quantities of urine would be produced."

What does it mean by "impermeable to water"? Can someone explain the mechanism behind losing a lot of water and making urine but having the collecting duct impermeable to water

Thank you!

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[themrn]

w/o ADH, the collecting duct is impermeable meaning that no H2O can be reabsorbed, so you produce urine with much water.

 

[denttal]

I often get confused by this too. For everything in the nephron, any "reabsorption" is back into the bloodstream/back into your body. Any "secretion" is into the nephron aka will eventually leave the body.

When I think of ADH, I think don't pee a lot. So if you don't pee a lot, you need to reabsorb water back into your body. On the other hand, a lack of ADH will cause you to urinate a lot of urine.

The collecting duct is a place in the nephron where you reabsorb water back into the body. So a LACK of ADH, meaning you will pee a lot, will cause you to NOT be able to reabsorb water back into the body (it won't be permeable to water).

 

[Psa]

Thank you both It makes sense. I thought maybe, collecting duct being impermeable to water meant that water wouldn't even make it there or something.