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NBME 22 Answers

nbme22/Block 2/Question#41

A 12-year-old boy is swimming in a mountain stream. ...

Central blood volume: increased;
Serum ADH (vasopressin): decreased;
Serum atrial natriuretic peptide: increased


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 +9  upvote downvote
submitted by keycompany(122),

Answer: Increased Central Blood Volume (CBV), Decreased ADH, Increased ANP.

The physiological response to hypothermia is vasoconstriction of peripheral vessels (i.e. the ones in your extremities) in an effort to keep your core body temperature normal, and thus your organs functioning properly. Peripheral Vasoconstriction will increase CBV. Increased CBV will cause an increase in preload, and thus cause an increase in ANP/BNP. ANP/BNP has inhibitory effects on the Renin-Angiotensin-Aldosterone System, resulting in decreased ADH.





 +2  upvote downvote
submitted by yotsubato(282),

What happens when you go into cold water? You pee.

How does this happen.

Vasoconstriction of vessels to preserve heat, pulls water into vasculature due to decreased hydrostatic pressure in vessels. Volume goes up, ADH goes down, ANP goes up due to increased volume.





 +0  upvote downvote
submitted by bubbles(31),

Wouldn't constriction of peripheral vessels also trigger sphlancnic vasoconstriction, which simulates renal ischemia and causes increased RAAS activity?

drdoom  Constriction of peripheral (cutaneous) arterioles/capillaries in response to cold surroundings is an attempt to reduce heat loss & maintain internal body temp; it is not at all coupled with splanchnic vasoconstriction. In fact, the peripheral vasoconstriction is trying to “re-route” blood to more internal/visceral compartments; simultaneous splanchnic vasoconstriction would impede that very process! +7  
bubbles  Ah, okay! I got led off track because I had a bunch of super hard practice questions asking about hepatorenal syndrome and how the constriction of sphlancnic vessels might trigger renal ischemia. Do you know if there would ever be a time when sphlancnic vasoconstriction occur outside of hepatorenal syndrome? +  
drdoom  @bubbles i would think only in cases of catastrophic shock (when the body is doing everything it can to maintain central tension; pressure to vital organs like heart,kidneys); in those cases, i could see the body sacrificing visceral flow as an "option of last resort" +  




I missed this as well because I completely overthought it since they had to add (vasopressin) instead of just saying ADH which made me think of its role in constriction of smooth muscle, but the point is that there will be pooling of the blood volume in the viscera and vital organs which will increase ANP release from the atria and since ANP is released with higher blood volume/atrial stretch, you can draw the conclusion that ADH will be low because ANP is signaling to the kidneys that there is an abundance of volume. Also, since the viscera is going to get more blood flow compared to the extremities since he is going to be hypothermic, you should also get increased flow to the kidneys or at least preservation (to a certain extent) and this would not promote the release of ADH which is only released when the body senses an increase in blood osm.





Central Blood volume refers to the blood in the central or cardiopulmonary compartment. During cold temperature there is peripheral vasoconstriction to prevent heat dissipation from the extremities which means there is less blood in the peripheries and more in the central compartment –> Central Blood volume increases Greater volume in the heart will cause stretching of the atrial wall and stimulate ANP release  increased ANP High Central blood volume  high volume state  downregulates ADH secretion  normal/decreased ADH





Central Blood volume refers to the blood in the central or cardiopulmonary compartment. During cold temperature there is peripheral vasoconstriction to prevent heat dissipation from the extremities which means there is less blood in the peripheries and more in the central compartment –> Central Blood volume increases Greater volume in the heart will cause stretching of the atrial wall and stimulate ANP release  increased ANP High Central blood volume  high volume state  downregulates ADH secretion  normal/decreased ADH





This question has nothing to do with temperature (the vignette doesn't address the temperature of the water - so don't assume)

This is how you get the answer:

1) Being in outer-space or in a swimming pool up to the neck will:

a. Increases Central blood volume (more blood returns to the right side of heart = increased preload)

b. Increases ANP = increased dilation of ventricles ~ compensatory mechanism to reduce volume overload

c. Decreased ADH & Renin-aldo-system = body is in state of volume overload & needs to reduce systemic volume

usmleuser007  correction: yea it does address the water temp but the main take away is increased preload +