NBME 22 Alteration of the thermostatic set point (NBME Answers)

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Retired NBME 22 Answers

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A 35-year-old man is brought to the hospital ...
Alteration of the thermostatic set point 🔍 / 📺 / 🌳 / 📖
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submitted by ∗keycompany(351)

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Alteration of the thermostatic set point is a hypothalamic process mediated by prostaglandins and is independent of the sympathetic nervous system.

B, C, D, and E all require sympathetic nerves to ellicit a response.

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pg32 Can anyone explain the mechanism behind shivering and the sympathetic nervous system? +4

mdmikek89 Hypothalamus relays through the autonomic nervous system. You cut the relay, you can only change the thermostatic set point, but the body can't react. +1

umpalumpa Guys, I think that for the shivering alternative the point is NOT that sympathetic nerves control shivering (actually, I haven't found articles on pubmed that says that shivering is controlled by sympathetic). THe easiest way to think is that this pt has a systemic infection (aka SIRS-systemic inflammatory response syndrome). In SIRS, pt can have T<35 C or >38 C, BUT it is more common to have fever than hypothermia. Considering this, you can easily rule-out the shivering alternative. +1

Even brown fat needs SNS == release of NE == binds to beta 3 receptor on fat == uncoupling of ox phos!

+6/- apurva(101)

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submitted by ∗qfever(67)

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Hypothalamus controlling temperature set point is briefly mentioned in Pathoma 2018 edition page 13, Chapter 2 III Cardinal signs of inflammation D. Fever

Pyogenes -> macrophage release IL-1 and TNF -> increased cyclooxygenase activity in hypothalamus perivascular cells -> increased hypothalamus PGE2 -> raised temperature set point

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submitted by gribear(0)

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Can someone explain why when you transect the spinal cord superior to the level of sympathetic outflow -- and you get a systemic infection -- the response is alteration of the thermostatic set point?

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its_raining_jimbos So I chose that one because set point is controlled by the hypothalamus (PGE2 and IL-1 mediate fever in the hypothalamus) and the rest of the answer choices involved something below the level that has been transected. Not 100% sure if that’s accurate though. +5

noselex Agreed with @its_raining_jimbos -- Fever is mediated by altering set point in hypothalamus. All the other choices, as far as I can tell, involve sympathetic nerves and their effects at target organs. +2

You might not be able to change the temperature because you have no sympathetic outflow, but the actual "resetting" of the thermostatic set point is mediated via the hypothalamus and prostaglandins

+2/- spow(50)

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submitted by ∗j000(17)

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i got this question wrong, but i think what this question is really asking is what happens in a systemic infection: which is fever

in systemic infection, the most obvious sign to look for is a fever, not necessarily shivering, sweating, heat production by brown fat, etc.

and how does fever occur? like someone already mentioned: pyogenes --> macrophages releasing IL1 and TNF which increases COX activity in hypothalamus perivascular cells, increase production of PGE2 in hypothalamus and reset the temperature set point.

i think the whole phrase "complete transection of the spinal cord superior to the level of sympathetic..." is a distraction. it just tells you that development of a fever has nothing to do with it

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j000 development of a fever in systemic infection has nothing to do with sympathetic nervous flow, so even it's injured, fever would still occur. I think this question is just asking how does fever occur in inflammation/infection situation. +1

b1ackcoffee So, how do you explain the actual fever by just changing the thermostat?? Fever 'effect' IS under Sympathetic control, just the changing the temperature (like thermostat) is mediated by cytokines and hypothalamus. +2

j000 oh i see what you mean, well i didn't know that, so thanks for clarifying that. however, based on your explanation, it would still get us to the right answer which is "alteration of thermostatic set point", not the fever effect itself. +1

So, how do you explain the actual fever by just changing the thermostat?? Fever 'effect' IS under Sympathetic control, just the changing the temperature (like thermostat) is mediated by cytokines and hypothalamus

+1/- b1ackcoffee(115)

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submitted by ∗mdmikek89(6)

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Okay boys and girls this question is easier than you think.

Hypothalamus relays via the sympathetic nervous system to control the body when a new set point as been reached in lets say...fever...cause by....infection.

If the connection between the hypothalamus and spinal cord (mainly the sympathetic outflow) is cut, the thalamus cannot relay the body reaction of a fever, but the hypothalamus itself can still change the set point.

Boom

Within the brain, the autonomic nervous system is regulated by the hypothalamus. Autonomic functions include control of respiration, cardiac regulation (the cardiac control center), vasomotor activity (the vasomotor center), and certain reflex actions such as coughing, sneezing, swallowing and vomiting.

B-E occur as a result of a change in set point.

A happens to cause the B-E when a new set point is reached.

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submitted by ∗isaacyo94(13)

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In systemic infection, wouldn't you get cutaneous vasoDILATION (i.e. distributive shock)? This was my reasoning for choosing B) in this wacky question.

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neilfespiritu Same +1

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submitted by ∗gh889(154)

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From ShoryukenHadooken on reddit:

What the question is getting at is the sympathetic chain was spared. It was a terrible way of wording it.

Your anterior hypothalamus is responsible for cooling features and is under parasympathetic control. A lesion would cause hyperthermia.

Your posterior hypothalamus is responsible for heating when you're cold and to generate the Fever response and is under sympathetic control. A lesion would cause hypothermia.

In this question it is simply asking a person gets sick, hypothalamus was spared, what happens.

Answer: hypothalamus will still be able to elevate set body temperature to battle infection.

Hint: IF they give a question similar to this but reworded to include a lesion of the sympathetic fibers or of the hypothalamus, you would in turn NOT be able to generate a fever response to infection. The hypothalamus would be entirely under parasympathetic control

This adds more context to the fact the Q states that the sympathetics was spared

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oslerweberrendu So, this says sympathetic also spared and hypothalamus also spared. Then what was wrong with this clinical case?? +1

adong i think the sympathetic system is actually impaired b/c it's cut before it can "outflow"...at least it's the only way this makes sense +4

suckitnbme I agree. I think the question stem is saying the sympathetics were lesioned. Not that they were spared. +4

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