kidney osmolarity

[soby10]

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Can someone figure out the reasoning on this. I chose A which is wrong, I figured if your lose blood volume you want to increase it by increasing the osmolarity therby reabsorbing more H20. Maybe immediately has something to do w/ the answer. Is increasing bp via osmolarity too slow?

Severe hemorrhage can greatly reduce the volume of extracellular fluids and reduce the blood pressure to the point of circulatory shock. Which of the following will occurr immediately after severe hemorrhage?

A) Increase osmolarity of extracellular fluids

B) Dilation of arterioles to increase venous return

C) Decreased volume of urinary output

D) None of the above

 

[soby10]

Ok so I think I understand, A is correct, C is correct and B is correct all will increase BP but the question states immediately therefore the fastet process is B) Dilation of arterioles to increase venous return. The others will work but slower.

 

[MT Headed]

Which of the following will occurr immediately after severe hemorrhage?

A) Increase osmolarity of extracellular fluids
B) Dilation of arterioles to increase venous return
C) Decreased volume of urinary output
D) None of the above

If you go with (B), you just increased the size of your pipes without increasing the amount of fluid in the pipes. BP will drop. I think you just killed your patient.

If you go with (A), remember that (for the purposes of the mcat) osmolarity is a sucking force, so this would cause fluid to move out of the cells and into the ECF (blood plasma where we need it and interstitial fluid where we don't). It might work, though it would be slow and your patient would still die.

With (C), decreased urinary output means fluid remains in the blood where it is so desperately needed. Again it's a slow solution.

Then we have (D). This is a severe hemorrhage. The patient is going into circulatory shock. These are the sorts of things that kill my patients before the ambulance drops them off at the hospital. This problem needs to be fixed NOW! What a body is most likely to do first is massively constrict all of the vascular system to raise blood pressure, and it will even clamp off certain unnecessary organs like the kidneys and digestive system completely. I'm liking D the best.

I admit, (A) and (C) are okay answers, but when I see phrases like "severe hemorrhage", "circulatory shock", and "occur immediately", I'm thinking A and C are a little bit like closing the barn door after the horse ran out.

 

[Temperature101]

Can someone figure out the reasoning on this. I chose A which is wrong, I figured if your lose blood volume you want to increase it by increasing the osmolarity therby reabsorbing more H20. Maybe immediately has something to do w/ the answer. Is increasing bp via osmolarity too slow?

Severe hemorrhage can greatly reduce the volume of extracellular fluids and reduce the blood pressure to the point of circulatory shock. Which of the following will occurr immediately after severe hemorrhage?

A) Increase osmolarity of extracellular fluids

B) Dilation of arterioles to increase venous return

C) Decreased volume of urinary output

D) None of the above

What is the right answer?

 

[paul411]

For the MCAT, increased blood volume = increased blood pressure.

To increase BP, you want to increase circulating blood volume.

A and B will decrease BP. Only C will raise BP.

 

[Temperature101]

For the MCAT, increased blood volume = increased blood pressure.

To increase BP, you want to increase circulating blood volume.

A and B will decrease BP. Only C will raise BP.

Thanks... I would have gotten it right then.

 

[soby10]

The answer is B) Dilation of arterioles to increase venous return
per TPR. All the others will actually increase BP, the only reason B is right is bc of rate. To increase BP immediately dilation would be the fastest route. How else can you distinguish A from B from C as they all raise BP?
Increase osmolarity of ECF will push h20 out via osmosis thereby increasing h20, decreasing urinary output will also increase bp, and bp is always increased w/ increasing venous return.

 

[gordonaasen]

DO you have any update on role of Na and Cl in kidney osmoregulation.

 

[MT Headed]

Okay I was a little confused about ECF, blood plasma, and interstitial fluid. I updated my earlier response.

But I still fail to see how answer (B) will raise the BP anywhere in the body. This seems like one of those lousy test-prep questions where I roll my eyes and move on. I can only hope that the real MCAT isn't this bogus.