Aamc 4 # 135

[brownhamster]

Fever in septic shock leads to which of the following compensation mechanisms?

A. Dilation of capillary beds in skin.
B. Increased skeletal muscle activity.
C. Decreased respiration rate.
D. Decreased fluid loss.

Correct answer is A. I chose B.
I don't completely understand their rationale, and I don't think my logic was far off.

Anyone see a hole in my reasoning?

From what I understand, you get a fever when the "thermostat" in your hypothalamus is set at a higher temperature. So instead of 98.6 F, it will set the new "normal" to 102 F. So your body, trying to reach the new set point, will perceive itself to be cold, and start to increase body temperature. One of those ways is to start shivering, which lead me to "increased skeletal muscle activity". Dilation of capillary beds implies that the body is trying to lose heat, which doesn't seem to make sense, when the the body is trying to increase temperature to meet the new set point. So maybe they want us to think it overshot? Perhaps I'm missing something.

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[ForumMember]

Choice B cannot be correct because it would not be a compensation mechanism. It increases the body temperature it does not decrease it. However, I don't think A is completely right either, but it is the best choice presented. I don't think blood vessel dilation is to compensate for heightened temperature, considering that your body is attempting to keep its temperature high to fight off the infection. The blood dilation is caused by cytokine release to fight infection not as a compensation mechanism to lower the fever. This is how I understand it (could be wrong). Perhaps, somebody else with more knowledge can explain it.

Otherwise, I would say realize that choices B, C, D are definitely incorrect and pick choice A because it is the only answer that fits the question.

(Also, if the temperature was overshot like you said, then blood vessel dilation would be a compensation mechanism. Out of the answer choices, it is the only possible compensation mechanism, so I guess in that very convoluted sense it is correct. I think the test-writers were just trying to test negative feedback here but did a poor job.)

 

[brownhamster]

yeah, I see what you're saying. I guess I should review the definition of "compensate".....

 

[Charles_Carmichael]

Anyone see a hole in my reasoning?

From what I understand, you get a fever when the "thermostat" in your hypothalamus is set at a higher temperature. So instead of 98.6 F, it will set the new "normal" to 102 F. So your body, trying to reach the new set point, will perceive itself to be cold, and start to increase body temperature. One of those ways is to start shivering, which lead me to "increased skeletal muscle activity". Dilation of capillary beds implies that the body is trying to lose heat, which doesn't seem to make sense, when the the body is trying to increase temperature to meet the new set point. So maybe they want us to think it overshot? Perhaps I'm missing something.

The hole in your reasoning is that you're thinking that a response to fever is shivering, which would further increase temperature. That's not true because, according to the question, you're already at the point of having the fever. You're not trying to reach that higher temperature. The question stem has already established a fever, so you can eliminate answers that lead to a fever right away. That includes shivering. And choices C and D don't make sense when discussing compensatory mechanisms in response to fever. Another way to think about this: when you already have a fever (higher body temp), does it make more sense to increase the temperature even further or decrease it? Then, look at the answer choices and eliminate the ones that don't make sense (ie. those that further increase body temp).

Now, what you have to know about the capillaries in the skin is that they play very important roles in thermoregulation. When the body is cold and needs to retain heat, the capillary beds in the skin are essentially closed. This means that no blood can flow through (because if the warm blood flowed through the capillaries, it would give off heat to the colder surroundings...aka, you'll lose heat). However, when the body has excess heat, like when you have a fever, those capillaries open up and blood flows through. Now, the blood can give off heat to its surroundings and thus, cool down during the process. Make sure you understand that. Skin plays a very important role in regulating body heat. Just knowing this little bit of info would immediately point you towards the right answer.

Hope this helps.

 

[Charles_Carmichael]

yeah, I see what you're saying. I guess I should review the definition of "compensate".....

When you see the word "compensate," rethink the question as asking "What is the response to..." For example, your question asks "Fever in septic shock leads to which of the following compensation mechanisms?" Rephrase this question in your head to "What is the response to fever in septic shock?" Now, the question seems simpler and easier to understand (ie. now, it's easier to recognize that the fever is already established and the question is asking you what happens afterward in response to it).

Hope this helps.