Does Aldosterone increase blood osmolarity?

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EECStoMed

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Does Aldosterone increase blood osmolarity? I know that it increases Na absorption and K secretion in the distal tubules but does it actually increase or decrease the plasma osmolarity? It increases BP yes, but what about solute concentration with the added water uptake?

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Does Aldosterone increase blood osmolarity? I know that it increases Na absorption and K secretion in the distal tubules but does it actually increase or decrease the plasma osmolarity? It increases BP yes, but what about solute concentration with the added water uptake?
From wikipedia :D

....aldosterone, which increases sodium reabsorption from the urine, sweat and the gut. This causes increased osmolarity in the extracellular fluid which will eventually return blood pressure toward normal.

EK audiosmosis says the same as does my Berkeley Review text.
 
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i dont think thats right. ADH and aldosterone serve to increase blood pressure by increasing water absorption. Since they both increase blood volume, osmolarity of the blood goes down (smaller ratio of dissolved stuff to blood fluid).

Although aldosterone causes increased absorption of Na+, the blood pressure was low to begin with, which means that the blood volume is low, which means that the concentration of stuff in the blood (compared to how much fluid is in the blood) is high. so, aldosterone is secreted, Na+ is absorbed, water absorbed too, and the blood volume is higher, which makes the osmolarity of the blood lower.

so, both, ADH and aldosterone serve to decrease blood osmolarity. Does this logic seem reasonable?
 
i dont think thats right. ADH and aldosterone serve to increase blood pressure by increasing water absorption. Since they both increase blood volume, osmolarity of the blood goes down (smaller ratio of dissolved stuff to blood fluid).

Although aldosterone causes increased absorption of Na+, the blood pressure was low to begin with, which means that the blood volume is low, which means that the concentration of stuff in the blood (compared to how much fluid is in the blood) is high. so, aldosterone is secreted, Na+ is absorbed, water absorbed too, and the blood volume is higher, which makes the osmolarity of the blood lower.

so, both, ADH and aldosterone serve to decrease blood osmolarity. Does this logic seem reasonable?

Correct, the only osmolarity importance is that at the venules... You need to understand what osmolarity is. It is the sucking of fluids in... due to the solute concentration of the given area. So, for blood, the arterioles at the capillaries release fluid per hydrostatic pressure which is the blowing out pressure from a force such as the force generated from the left ventricle during the intial push of the blood from the heart that is oxygenated... This blood goes throughout the body until it leads to the areterioles which demonstrate the hydro fluid out and on the venules side of the caps are the osmotic pressure which is sucking interstial fluid back in.

So, NO, aldosterone has nothing to do with this process... Aldosterone is the kidney's way of saying here is the piss and we need to prepare to eject it so lets first take some water after the PT reabsorption and secretion of last nights beer, down the loop which only lets out water gearing of for pressure, then up the loop of henle to not take any water but rather release some Na so that the pressure really builds in the nephron due to osmotic pressure, as it goes to the distal tubule this is where the adrenal cortex says OK, pressure isn't enough so I am going to cause a little Na/K pump action and get even more solute out to the nephron side and take up some H2O which can even further be aided by ADH to increase water absorption by Nephron... CAUSING more pressure... Why? the body might need a higher blood flow in especially the symp pathway that require fight or flight.

Again, aldosterone is going to only add to the Na / K pump at the kidney... taking up Na and causing pressre and releasing K into the piss.
 
i dont think thats right. ADH and aldosterone serve to increase blood pressure by increasing water absorption. Since they both increase blood volume, osmolarity of the blood goes down (smaller ratio of dissolved stuff to blood fluid).

Although aldosterone causes increased absorption of Na+, the blood pressure was low to begin with, which means that the blood volume is low, which means that the concentration of stuff in the blood (compared to how much fluid is in the blood) is high. so, aldosterone is secreted, Na+ is absorbed, water absorbed too, and the blood volume is higher, which makes the osmolarity of the blood lower.

so, both, ADH and aldosterone serve to decrease blood osmolarity. Does this logic seem reasonable?
Yes you are correct...I didn't realize water was also being taken up along with the Na+ :(
 
Okay, you guys are weirding me out! Here is what it says in the princeton review book about aldosterone:

"When the blood pressure is low, aldosterone is realeased by the adrenal cortex. It causes increased reabsorption of Na+ by the distal nephron. The result is increased plasma osmolarity, which leads to increased thirst and water retention, which raises the blood pressure."

Is blood osmolarity the same as plasma osmolarity?

ADH is a different story however (it causes water absorption, by making the distal nephron more permeable to water)...It works in conjunction with aldosterone to increase BP...
 
I guess it just depends on how you look at it. Before aldosterone is released, surely there's low blood volume (because this in effect means there was low blood pressure; low blood volume means more solute than water in the blood, causing aldosterone to be released in the first place). So, when Na+ is absorbed, water is absorbed too, which increases blood volume and decreases blood osmolarity.

However, in the immediate vicinity of the kidney, suddenly increasing Na+ absorption will make that immediate blood vessel more hypertonic (higher osmolarity), which causes water to flow from the collecting duct to the blood.

Third, I dont think we should be overly concerned with whether aldosterone increases or decreases blood osmolarity. I think ADH deals with osmolarity balancing (low osmolarity increases ADH secretion, which increases water absorption). Aldosterone is in response to low volume or low pressure in the blood, and does not necessarily have much to do with blood osmolarity. Now, it probably does have SOMETHING to do with it, but there is so much more biology for them to test us on, that this small fact seems quite irrelevant.

I dunno, i'd appreciate it if someone could clear it up once and for all, cuz all these damn test prep companies say different things. But until then, it's time for the rest of the endocrine system! :laugh:
 
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ADH and Aldosterone both serve to increase BP, however they do it in somewhat different fashions. As you know, ADH directly reabsorbs water out of the collecting duct into the blood stream. Aldosterone reabsords Na back into the blood stream, which at that point, yes- it would increase blood osmo....BUT due to osmosis water flows from the collecting duct into the bloodstream which in turn decreases blood osmo.
 
ADH and Aldosterone both serve to increase BP, however they do it in somewhat different fashions. As you know, ADH directly reabsorbs water out of the collecting duct into the blood stream. Aldosterone reabsords Na back into the blood stream, which at that point, yes- it would increase blood osmo....BUT due to osmosis water flows from the collecting duct into the bloodstream which in turn decreases blood osmo.

short and simple. i think i like this. :idea:
 
Because all these test prep companies say it differently, it might be better to look at it from the change in blood volume instead of osmolarity.
 
so from what i can gather from you guys...

short term and around kidney tubles ====> Na+ absorbed and thus blood osmolarity increases

long term===> water diffuses accros nephron to blood to decrease the osmolarity and thus increase blood pressure...

am i right?
 
so from what i can gather from you guys...

short term and around kidney tubles ====> Na+ absorbed and thus blood osmolarity increases

long term===> water diffuses accros nephron to blood to decrease the osmolarity and thus increase blood pressure...

am i right?

that is how i see it
 
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Ok so let's end the drama with the aldosterone. Im looking at my EK book (6th ed.) and it seems that blood osmolarity goes down with ADH and aldosterone but Aldosterone alone seems to either raise or have no effect on osmolarity since NA gets reabsorbed but K+ gets secreted (solute flow goes both ways).
Does this forum concur these claims?
 
Ok so let's end the drama with the aldosterone. Im looking at my EK book (6th ed.) and it seems that blood osmolarity goes down with ADH and aldosterone but Aldosterone alone seems to either raise or have no effect on osmolarity since NA gets reabsorbed but K+ gets secreted (solute flow goes both ways).
Does this forum concur these claims?

Agreed. :thumbup:
 
so from what i can gather from you guys...

short term and around kidney tubles ====> Na+ absorbed and thus blood osmolarity increases

long term===> water diffuses accros nephron to blood to decrease the osmolarity and thus increase blood pressure...

am i right?

but the osmolarity is really the nephron... Not the blood... there is a difference. The but then again it is both but you have to understand how it is in both places... The blood is only effected from the fenstrations in the glomarulous... then after that you are dealing with nehpron NA and H20... later you get aldosterone and ADH...
 
but the osmolarity is really the nephron... Not the blood... there is a difference. The but then again it is both but you have to understand how it is in both places... The blood is only effected from the fenstrations in the glomarulous... then after that you are dealing with nehpron NA and H20... later you get aldosterone and ADH...

You are going into way too much detail for the MCAT. This type of information would be in a passage if it were to be tested. What we should have down is what ADH and Aldosterone act on, in response to what, how they do it, and what the end result is.
 
AWhitehair is right... let's keep this discussion strictly MCAT and not over analyze.
 
osmolarity is defined as moles of solute per liter of solution. Aldosterone's primary purpose is to INCREASE BLOOD OSMOLARITY so as to increase water resorption and BP in times of need. Increasing blood osmolarity leads to increased water resorption, resulting in greater blood volume, greater end diastolic volume, greater stroke volume, and subsequently increased blood pressure.

Aldosterone release is stimulated by angiotensin II in times of low bp. This confirms the fact that the RAA system is critical for increasing bp. it serves to increase bp by a.) the activation of angiotensin (body's most potent vasoconstrictor-increased Total Periphreal Resistance and thus increased bp) and b.) activation of aldosterone.
 
osmolarity is defined as moles of solute per liter of solution. Aldosterone's primary purpose is to INCREASE BLOOD OSMOLARITY so as to increase water resorption and BP in times of need. Increasing blood osmolarity leads to increased water resorption, resulting in greater blood volume, greater end diastolic volume, greater stroke volume, and subsequently increased blood pressure.

Aldosterone release is stimulated by angiotensin II in times of low bp. This confirms the fact that the RAA system is critical for increasing bp. it serves to increase bp by a.) the activation of angiotensin (body's most potent vasoconstrictor-increased Total Periphreal Resistance and thus increased bp) and b.) activation of aldosterone.

so initially it increases blood osmolarity, but when all the water goes into the blood, osmolarity decreases.
 
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