NBME 23 Precapillary resistance (NBME Answers)

NBME 23 Answers ↦

nbme23/Block 4/Question#45 (84.6 difficulty score)
A 32-year-old man has a diastolic blood ...
Precapillary resistance🔍
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+38
submitted by ferrero(40),

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A vyer slarimi qisuteno I vaeh snee ni bsQkna llwi sak yhw a ptitean tiwh griht eatrh aleriuf does ton veldpoe demea dna eth nrasew si rdaeinsec htipymlca reinag.da I ogt ihst nutsoeiq rwgno liglyonair caeesub I rwnadees aongl siht niel fo sanirengo tbu I tnhki in shit asec ti all sah ot do thiw HREWE eth traxe seuersrp si giomcn or.mf In htis sqouneit hte tp ahs tdoiaclis nhionyrestpe os ouy nca nktih utabo teh sruerspe as onmcig rdofrw""a os gtitnncsoric apilaelryrcp eschnsrtpi can pnretve na ceirnsae in pruersse in the pliaylarc .ebd vwerHeo orf itghr herat laireuf ihst rxeat ldifu si nicgom omfr the EPOOPTIS nroetiidc akcrwas(bd frmo eth gthri hate)r dan ctntoingicsr paacllpryeri eirtscnphs nca do nghiotn n(o pipesoto dise of yilcaplra e)db - the olyn awy ot peevtnr demea si ot riaeencs aiplhtmyc dinraga.e

seagull The question clearly lead us to think about Osmotic pressure by talking about protein and urine. I wonder how many people used that line of reasoning (like myself)? +15

mousie Great explanation, I chose lymphatic drainage for the same reasoning (similar Q on different bank) +5

sympathetikey My reasoning was much more simplistic (maybe too simple) but in my mind, systolic BP is determined by Cardiac Output and diastolic BP is determined by arterioles. Therefore, what comes before the capillary and regulates resistance? Arterioles. That's why I said that pre-capillary resistance. +31

cr the main difference between the 2 cases is that in this case the patient has high BP +1

link981 So in kindergarten language the question is essentially asking how high pressure in the arterial system is NOT transmitted to the venous system (which is where EDEMA develops). But you know they have to add all this info to try confuse a basic principle and make you second guess yourself. (Got it wrong by the way) because of what @ferrero said of Qbank questions. +6

hello @ferrero what are you talking about? lymphatic drainage is the wrong answer... +1

hello ok never mind. i got it. hard to understand b/c it was a big block of text. +2

asteroides I think they may be talking about the myogenic compensatory mechanism: https://www.ncbi.nlm.nih.gov/books/NBK53445/figure/fig4.1/?report=objectonly "Increased arterial or venous pressure also induces myogenic constriction of arterioles and precapillary sphincters, which raises arteriolar resistance (thereby minimizing the increase in capillary pressure) and reduces the microvascular surface area available for fluid exchange. For example, because vascular smooth muscle in arterial and arteriolar walls contracts when exposed to elevated intravascular pressures, this myogenic response increases precapillary resistance and protects capillaries from a concomitant rise in their intravascular pressure." +3

usmleaspirant2020 https://www.memorangapp.com/flashcards/244421/Regulation+of+Blood+Flow/ this picture helps! +2

+2
submitted by notadoctor(151),

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vI'e bnee gnisahrce ofr ym ocruse rfo ihst tub cna't eesm ot ndfi .ti oewvHre, het way I gtuthoh uaobt it asw hatt aedme sephpan avi eht plcae.iilars fI eerht is nrcdesaei erecaintss via the arirapplcely htspecirsn as uhcm blodo dtuol'wn eb blae ot etg otin eht iipllsarac.e heT boodl lwodu endtsai get hsnedut iav eosnasmatso to eth isne.v ihsT arcliet mrfo oovligyyp.scomhc anpexsil it a titlle trbee:t CV yysooligP:h Tuseis aeEdm nad Gaelenr Pprenciils fo Tlcyaianaprlsr diFlu gaxhEenc

+2
submitted by staph_aureusxx(4),

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aiprpeylcral saenitrcse = rigbcndise het erla.oersti se'h tog iinamml etoprni ni het nieu;r adn on aumn.lbi the key saw gnpyia noitattne ot teh lobod eeprr.ssu eersrsPu si lgdueetra by the issetarcne sveesls as asodrb acsll it ihchw si eth seitaorlre aak pealripclyra e.sesarcnit

+1
submitted by chagas14(1),

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baMye hte nqtsouei si iandelg itwh teh tonccep fo mceygoin atrorreali covniocirtonstas ihwch si a onathre da-neimate immhscn.ea eTh per lpaliarcy etpchisnr tacctorn in sonreesp to a seair in .PB I got hte Q wngro eubcsae I cdiepk pticmlhay .wflo ehTy love ot go for the at"wh sl"ee tleeenm fo nay ti.pco I tanonc indf nya nsoaer yhw teh timpcyhla onitop doulc eb rgnow :/

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+0
submitted by usmleaspirant2020(6),

https://d1yboe6750e2cu.cloudfront.net/i/0b2159dfcfd96ee300a97e2e07d7d0c0229a2d3f

+0
submitted by ninja3232(7),

"When arterial pressure falls, myogenic tone is reduced in arterioles, decreasing their resistance to flow and maintaining capillary pressure. These observations suggest that capillary pressure may be regulated over the same range of pressure changes over which flow is autoregulated in a given organ. Indeed, from the relation:"

https://www.ncbi.nlm.nih.gov/books/NBK53445/

+0
submitted by adong(94),

In addition to what has already been said I think an important point in the question was regulatory adjustments which points more towards arteriolar regulation.

+0
submitted by hello(298),

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why is mapals ootincc uerpsers rw?ong

rainlad I think it's because we would expect to see some more proteinuria/albuminuria if the plasma oncotic pressure had increased to compensate +1

+0
submitted by ferrero(40),

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A ervy aimrlis qeistnou I vaeh enes in asnQkb ilwl aks why a pnieatt twih gthri tearh laufeir oeds ton pldovee meaed nad eth wrneas si secdreain aythlpcmi neaa.drgi I ogt shti tnoiequs orgnw ryoaillngi beeacus I dseenwar agnlo shti leni of enogianrs tbu I ikthn ni hsti csae ti lla ahs to od hiwt HEEWR the txrae speesurr si oncgim romf. In tihs tsoeiuqn teh pt ahs otaiiclds nrpseheioynt os uoy anc ntkhi uatob teh urepsrse sa nogimc f"wr"ardo so ccronstgtini piaeaprlrlyc epirtssnch nca etrnvpe na ersiecna in spurseer ni eht allcyipra d.eb oeHervw rfo hgrti eahrt rlfuiae isth rxaet fildu is gcnomi frmo het POTSIEPO ortinedci dbskc(awar ofmr teh rhgit hea)rt nad csntiroitcng arylceliparp ecnssthrpi nac od hntogin (on optisepo iesd of aycrlilpa ebd) - eth lnyo wya to etpenvr edema is to recansie yaitlcpmh e.gadainr

+0
submitted by usmleuser007(370),

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ocrtAi otclisiDa eesPrsru

iHgh TPR = hihg PD
ghHi HR = hgih PD
ihgH VS = high PD

roitcA lysticoS ssPruree

Hgih tioyrlnaitctC = ghih PS
gHhi VS = hhgi SP
owL nclmeCpaoi = ghih SP

-1
submitted by spow(29),

I also think that the point being made here is about mean arterial pressure (MAP), which is what autoregulatory systems actually change based on. Because he has increased MAP (due to increased DBP), the capillaries will constrict to maintain constant pressure/flow through the capillary bed.

-2
submitted by divya(58),

i don't think you need to think all that much. look at all the options and think of what happens when they increase. A, B, C, D and F all can cause interstitial edema. But increasing precapillary resistance definitely doesn't.

drzed Increased lymphatic flow would not cause interstitial edema. +1

123ojm but it doesn't say "increase in," it just says "regulatory adjustments in." +1

-3
submitted by usmleuser007(370),

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.1 Atiroc osDatlici seserurP 
    1. Hghi PTR = ihgh 
PD    .2 gihH HR = hhig 
DP    3. Hhig SV = ghhi DP .
2 rAocti tioysSlc ePrusres 
    1. hHgi cnayiiotrtClt = ighh 
SP    2. ihHg SV = hhig P
S    3. owL ceolpCinam = gihh SP

yex https://cvphysiology.com/Microcirculation/M012 This helps somehow, the first part about capillary pressure. +

usmlelol that's the exp part:: The average capillary hydrostatic pressure is determined by arterial and venous pressures (PA and PV), and by the ratio of post-to-precapillary resistances (RV/RA). An increase in either arterial or venous pressure will increase capillary pressure; however, a given change in PA is only about one-fifth as effective in changing PC as the same absolute change in PV. Because venous resistance is relatively low, changes in PV are readily transmitted back to the capillary, and conversely, because arterial resistance is relatively high, changes in PA are poorly transmitted downstream to the capillary. +