NBME 23 Precapillary resistance (NBME Answers)

NBME 23 Answers ↦

nbme23/Block 4/Question#45 (89.9 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 yver isralmi uisonqte I heav esne in Qbnaks lwli ska yhw a nteiatp hwti gtirh areht rafulei sedo ont epoledv dmeea nad teh arnsew si enearidcs itclhampy eiadrgna. I tog thsi sienutoq nrgow olilgryain eucaseb I neraweds naolg stih leni fo oeaignrns btu I itknh ni htis asce it lla ash ot od hiwt EWHER eth retxa rsprseue si icongm mrf.o nI ihst eqotsuni eth tp ash disoatilc ehrtnynposei os oyu acn ihntk oabut the rrseesup sa omngci da"rwf"ro os rcttiinncosg pyelripaarlc tschnieprs nac ntrvpee na rsaeecin in erprsues ni eht rpcyliala bd.e rweoveH for ihgrt tahre uaerlfi sthi xarte dfuil si nigmco mrfo hte IPOESPOT reitcdnoi cbdaarw(ks ormf eth irhgt ear)ht and girtitnnscoc iarlrplacype pthrcseisn anc do gotinhn n(o peotospi isde fo yralpclai b)ed - het nyol awy to nerptev meeda is to seinacer plyhmctai irnadag.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) +8

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 staph_aureusxx(4),

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ellryaipcrap tsraesceni = gbiescnidr teh selartrio.e hs'e ogt mniimal orteinp in het uenri; adn no ul.mbnai hte eyk saw anpiyg ntineatto ot het bodol eers.uspr sPersure si eealdgurt by hte etsreansci evsesls as osdarb llcas ti wihch si the earoetrils aak aplcearyplri isnsrtaeec.

+2
submitted by notadoctor(159),

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'eIv been hrgsaceni rfo my oeucsr ofr tihs tbu 'tnca msee to dnfi i.t ,voeerwH the ayw I hhtogut uoabt ti was atht aedem pspehna via eht a.eiilalpscr fI heert si riandesec irsancseet vai eht ayprlrapliec pricshesnt sa uhmc doolb wdl'outn be able ot get into teh rcepilsala.i hTe oodbl dwuol setnadi etg hutedns iva noosesaatsm to eht esi.vn isTh ricaelt rfom .yoopshccvmigoyl psalxien it a little er:tetb VC oyhoyi:gsPl siesTu Eedma nad eneGlra ieirnlcpPs fo srnlcaaiapyTlr udFil axcEgenh

+1
submitted by chagas14(1),

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yabMe hte nqtisoeu si adnlgie hitw eth nccetop of igncyoem rlaareirot ooacntvrtisonsic hwcih si a reatonh mtaneae-di .mimaescnh eTh erp cyprialal pesctirnh noctatcr in soeepsrn ot a areis in BP. I got het Q rgonw ebuasce I dpikec hcylmpait olwf. yTeh vole ot og rof eht tawh" se"le tlmenee fo nay ct.opi I tcnnoa fndi yan sronae hyw eth ymhpiclat pootin uodlc be rogwn /:

ht.BK4/coll/t.?srppgsonhrb5N/k.3mswnsooiwib/e:4c=i5tcw/av.nkc eCh hte ueirgf 1.4 heT aMngir of Seytaf tnsigAa eEamd ntraFiomo – daemE aSeyft osarFct

+0
submitted by adong(97),

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nI tidiaond to htaw sah aelrady enbe isad I inthk na iontmrtpa notip ni eth quetosin wsa rortyualeg esdjtmnsatu ciwhh tpsoin rome owsatrd raoaterril gtro.ulnaei

+0
submitted by usmleaspirant2020(7),

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 hello(317),

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ywh si msapal oncicto esrupesr wgo?rn

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 reyv salrimi itsuoeqn I evah esne in bsnkQa lliw ska hyw a ptteian wtih rhgti harte uiaferl odse otn depvelo meead nda teh anwser is edncerisa tailyphmc reaidg.na I ogt hist oneuiqts gworn oaigrnliyl eusebac I reaewsdn golan this lien of sgroienan but I tnkih ni siht acse it lal sah to do thiw REWEH eth erxat uresrspe is nmocig .mfor In tihs ueqiotns eth tp hsa ldaoiitsc eyhnentsirpo os yuo anc nhkti aobtu hte errespus sa icongm w"ofr"dra os itticnscgonr lcrpalyerpai eirtpsnshc can rtepven an rsiaceen ni resrepus in eht yrlplacai d.be eHrovew rfo hrtgi aerth aulifre siht raetx fldiu is nicgom rmof the IOPTOEPS rticdieno wbskc(rada omrf het rthgi ra)het dan csrnciottgin lypiacrlepar shecspirnt anc od ognthni (on ptspoeio idse fo plyalcria be)d - het ylno ayw to vrneetp eedam si ot aecnersi hpcayitml iaadr.gen

-1
submitted by usmleuser007(397),

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orAtic alotiDsic eserPr us

Hhig PRT = ighh DP
hHig RH = gihh DP
ihgH SV = ghhi PD

rAicot ylSostic eureP ssr

ighH iarlntytoCcti = ighh PS
hHgi VS = ihgh SP
woL pmalocneCi = hhgi SP

-1
submitted by spow(34),

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(59),

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i td'on nkith ouy eend ot kinth all hatt .mhuc oklo at all hte potiosn nda itnkh of wtah phsaepn nhwe teyh ,sce e.aAirn ,B ,C D nda F all nac caeus ireitstantli tme.uade B gniscairne iplalearprcy eicnearsst yflnetidei tnoe'ds.

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(397),

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.1 rcAoti liaiDotsc ePuerrss 
    .1 gHih PRT = ghih 
DP    .2 hgiH RH = hhig DP
    3. gHhi SV = ighh PD 
.2 Atorci iylSstoc eserusPr 
    .1 ghHi yottlCciatnir = ighh SP
    .2 Hhgi SV = hgih 
PS    3. Lwo mCclonpeai = gihh P
S

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. +