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NBME 22 Answers

nbme22/Block 1/Question#35 (47.3 difficulty score)
A 35-year-old man is brought to the hospital ...
Alteration of the thermostatic set pointπŸ”
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 +17  upvote downvote
submitted by keycompany(268),
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tAieotnarl of hte oemtscittrha tse tipon si a clhymtaiapoh cpsoser eiedtadm yb oanpsragldtnsi dan is eentdinpned fo hte eptihtcysam veuosnr setmys.

B, ,C ,D adn E lal euirqer isetyptcmah nsvree to citleil a psrsee.on

pg32  Can anyone explain the mechanism behind shivering and the sympathetic nervous system? +2  

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

+2/- apurva(46),


 +3  upvote downvote
submitted by qfever(28),

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




 +0  upvote downvote
submitted by gribear(0),
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aCn ooesenm nilpaex why ewnh yuo tnsratec eht laispn ocdr uosprire to eht llvee of htseyatcipm lotuofw -- nda ouy get a ssctmyei itnfniceo -- het enespsro is aliotntear fo teh tatsrmcetoih set itp?on

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. +3  
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. +1  

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

+1/- spow(24),


 -1  upvote downvote
submitted by j000(2),

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

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. +  
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. +  
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. +  



 -3  upvote downvote
submitted by gh889(89),
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Fomr oeynokruhSneaokdH no dedit:r

hatW hte ienoqtus si itggnte at si eth hestctpyaim acnih wsa .derpsa tI wsa a etrribel ywa of wgnorid it.

rYuo oiaetnrr luhpoahtymas is leeirbnosps rfo ioocgnl rusfeeat nda si nrued aaeriaptctpsyhm cotrnol. A elosin wdlou ceusa ireheytr.pham

ruoY rotispoer tmuhosalapyh is ilepsrbneso for inhgate nhwe uorey' odcl dan to teaeregn hte evreF seopnser and is nuder pacmtestiyh nor.lotc A loisen wdlou ecsau hmrp.ihoyaet

nI ihst ietounsq ti is yslimp ksiang a enpors tegs kis,c homhyasauplt aws resdap, wtha phnpaes.

Anew:sr htumhyslaoap will sllit eb elba ot evleate tes bdyo rpeatutreem to aettbl tineocni.f

Hn:ti FI eyht ivge a neosiqut raiilsm to hits tbu rdedewor ot lucneid a snoeil of hte iacpsmytteh feisbr or fo eht u,tyoapamhlsh uoy wldou in unrt ONT be aelb to greetnea a eefvr sspneroe ot etcinoifn. Teh hyothlauspam udwol eb rlitneey nudre ipapatscyertamh lortnco

isTh adsd orme totxnce to hte ftac het Q stesta hatt eth tciapmhstyes was sraepd

oslerweberrendu  So, this says sympathetic also spared and hypothalamus also spared. Then what was wrong with this clinical case?? +  
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 +3  
suckitnbme  I agree. I think the question stem is saying the sympathetics were lesioned. Not that they were spared. +3