Aldosterone vs. ADH osmolarity

[km1865]

Kaplan says Aldosterone does NOT change filtrate osmolarity (this makes sense since its primary function is Na+ ions, and as a RESULT water is also reabsorbed, therefore the osmolarity of the filtrate should be the same right since the two effects negate each other?) On the other hand, EK says the net effect of aldosterone is to lower osmolarity.. can someone confirm what's true?

Also, ADH always decreases osmolarity right since water is being reabsorbed without the reabsorption of ions so net result= osmolarity decreases?

THANKS!

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[muhali3]

Increased osmolarity means a more concentrated solution. It's pretty much the same thing as molarity.

So ADH would increase filtrate osmolarity.

Aldosterone increases Na+ absorption and K+ secretion. Water follows the sodium so blood volume and blood pressure increases.

I'm not sure about the effect on osmolarity. All you need to know for the MCAT is:

Aldosterone: Na+ absorption (primary effect). And increased blood pressure (secondary effect).

ADH: Increases blood volume/blood pressure (primary effect)

So, if you have to choose between ADH and aldosterone on the MCAT, know that aldosterone's primary function is to absorb minerals and that ADH's primary function is to increase blood volume/pressure.

 

[Nkeflin]

ADH increases reabsorption of water so yes, osmolarity of the blood decreases.

Aldosterone has more to do with maintaining blood pressure than blood osmolarity, so I wouldn't imagine you would have to worry about something like this on the MCAT. Regardless, in response to low blood pressure, aldosterone is secreted and acts on the cells of the collecting duct and distal tubule. reabsorbed ions create the osmotic gradient (an increase in osmolarity of the immediate blood vessel) that drives water out of the lumen of the nephron into the blood and interstitium. As a result, blood volume increases and blood osmolarity decreases