Kidney Question

[freedyx3]

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Hi here's a question for anyone who knows about kidney function

I can't seem to figure out something. Maybe i'm just ******ed. Ok the question is what effect does high concentrations of ADH have on urine and the answer is the urine becomes more concentrated. BUt how can this be. Urine is hypertonic to blood and ADH causes the nephron to be more permeable to water. So if urine is hypertonic to blood wouldn't high levels of ADH cause water to rush into the urine and make it more dilute???

man i'm confused.

 

[DMX9911]

Hey freddy,

ADH increases water reabsorption in the collecting tubule cells by increasing the # of lumenal membrane channels in the collecting duct cells.

It does this through the insertion of water channels into the lumenal membrane.

The concentration of water is higher in the lumenal filtrate than in the cytosol (not blood), so water goes out.

I think you're confused cuz there is an interstitium (lumenal cell membranes) that surround the tubule lumen (where the filtrate is) before it exits into the capillaries. ADH acts on the intersitium which in turn interacts w/ the filtrate. So blood concentration is not a factor.

 

[Supernumerary]

Well, I've been in the South long enough to have learned this about kidneys - they ain't fit fer eatin'.

 

[UBTom]

to Freedyx3:

The easy way to think about it is this:

antidiuretics makes one urinate less. Urinating less = smaller volume = less water in the urine = more concentrated urine.

diuretics makes one urinate more. Urinating more = larger volume = more water in the urine = less concentrated urine.

HTH!

 

[tinker bell]

ADH affects on reabsorption of water. So, water in the collecting tubules goes back to blood, leaving urine with very little water, and large volume of blood. This will increase blood pressure.

Remember that on the DAT, the blood pressure question always goes with ADH. They love it.

 

[grettlin2]

This is the way I use to convince myself about this question.

The only part that nephron would deal with blood is Bowman's capsule + glomerulus. Then, the fluid and small solutes would enter the nephron and the water is reabsorbed at proximal covoluted tubule ==> First time. Then, the a little bit more concentrated filtrate would experience osmosis in medulla. Then, the water is removed again. ==> Second time. While the filtrate arrives collecting tubules, ADH hormone releases and this hormone allows only "ONE WAY" for water to move out of the collecting duct. ==> Third time to make the urine even more concentrated.

This is the part I am not quite sure, either. Forgive me if I am not correct and let me know the reason. Thanks!