呼吸科呼吸系统课件.ppt
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呼吸科呼吸系统课件.ppt
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5.2.5.2.GasExchangeGasExchange2022/11/51lDefinitionlDiffusionofoxygenandcarbondioxidebetweenthealveoliandthebloodinsidethepulmonarycapillaries.lWhatwehavetoknow?
lBasicprinciplesofgasdiffusionlFactorsthatdeterminetherateofgasdiffusionPartialPressureofIndividualGasesinaGasPartialPressureofIndividualGasesinaGasMixtureMixtureAbovetheabsolutetemperature,allmoleculesofallmatterarecontinuallyundergoingmotion.Pressureiscausedbymultipleimpactsofmovingmoleculesagainstasurfaceeitherinair,liquidorotherformsofmatter.Thepartialpressureisdirectlyproportionaltotheconcentrationofthegasmoleculeforair.2022/11/52AppliedGasLawsAppliedGasLawsQuestionnAtthesealevel(barometricpressureis760mmHg),howmuchisthepartialpressureofoxygenifweknowairconsistsof21%oxygen?
HintsnDaltonslawstatesthatthetotalpressureexertedbyagaseousmixtureisequaltothesumofthepartialpressuresofeachgascomponentinthegasmixture.nInamixtureofgases,thepartialpressureofagivengasisdirectlyproportionaltothevolumethatgascontributestothetotalvolume.2022/11/53AnswersAnswersPB=PN2+PO2+PHO2+PCO2(atthesealevel,PB=760mmHg).WherePB=barometricpressureatthesealevel.WherePN2isthepartialpressureofnitrogen.PO2isthepartialpressureofoxygen(氧分压).PO2intheair=760mmHgX0.21=160mmHg.2022/11/54PartialPressuresofIndividualGasesatthePartialPressuresofIndividualGasesattheSealLevel(PSealLevel(PBB=760mmHg)=760mmHg)2022/11/56AmbientDryair(mmHg)MoistTrachealAir(mmHg)AlveolarAir(mmHg)SystemicArterialBlood(mmHg)MixedVenousBlood(mmHg)O21601501029540CO200404046WaterVapor047474747N2600563571571571Total760760760760704WaterVapor(WaterVapor(水蒸汽)水蒸汽)LowersPOLowersPO22onceAironceAirIsBeingHumidifiedIsBeingHumidified(湿化)(湿化)Airisbeingwarmedandhumidifiedbeforereachingalveoli.WatervapordoesnotchangethepercentageofO2orN2butdoeslowthepartialpressureofO2orN2.Inhumidifiedair,nPO2=(76047)X0.21=150mmHgnPN2=(76047)X0.79=563mmHg2022/11/57ThePartialPressureofOxygenintheThePartialPressureofOxygenintheAlveolarSpaceisdownto102mmHgAlveolarSpaceisdownto102mmHgTworeasonscausethis“down”TheexistenceofFRCresultsindilutionofairinthealveoli.Thecontinuousuptakeofoxygenbythebloodinpulmonarycapillaries.2022/11/58TheDeterminantsofAlveolarPTheDeterminantsofAlveolarPOO222022/11/59FactorsthatDetermineAlveolarPCOFactorsthatDetermineAlveolarPCO222022/11/5102022/11/511DiffusionofGasesthroughtheDiffusionofGasesthroughtheRespiratoryMembraneRespiratoryMembrane2022/11/5122022/11/512Alveolar-CapillaryMembrane(RespiratoryMembrane)2022/11/512Sixlayersconstructabarrier1.Alveolarfluidlayer2.Alveolarepithelium3.Alveolarbasementmembrane4.Interstitialmatrix5.Capillarybasementmembrane6.CapillaryendotheliumGasesDiffuseaccordingtoTheirGasesDiffuseaccordingtoTheirConcentrationGradientsConcentrationGradients2022/11/5131.Bloodstaysinthepulmonarycapillariesfor0.75seconds.2.Ittakes0.25secforO2toreachtheequilibrium.3.PO2inthepulmonarycapillaries,pulmonaryvein,andsystemicarteriesshouldbecloseoridenticaltothatinalveolarspace.WhyisArterialPOWhyisArterialPO22LowerthanThatofLowerthanThatofAlveolarAir?
AlveolarAir?
2022/11/514nTwocontributors:
ashuntandalowventilation/perfusionratio.nTheconductingairwayshaveaseparatecirculation,calledbronchialcirculation.nAbouthalfofvenousbloodfromthebronchialcirculationreturnstothepulmonaryveins,resultinginanadmixtureofunoxygenatedbloodandoxygenatedbloodandadropinarterialPO2.QuantitativeDescriptionofDiffusionQuantitativeDescriptionofDiffusionFickslaw:
D=P.T.A.S/d.(MW)1/2WhereD=diffusionrateP=partialpressuregradient(drivingforce)T=temperatureA=membranesurfaceareaS=solubilityofgasinthebloodd=distanceofdiffusion(thethicknessofmembrane);MW=moleculeweightofthegas.S/(MW)1/2isalsodefinedasdiffusioncoefficient(扩散系数).2022/11/515BetweenOxygenandCarbonDioxide,BetweenOxygenandCarbonDioxide,WhichGasDiffusesFaster?
WhichGasDiffusesFaster?
ConclusionslAtthesamepressuregradient,carbondioxidediffuses24.3timesfasterthanoxygen.lUnderphysiologicalpressuregradients,carbondioxidewilldiffuse2.35timesfasterthanoxygen.2022/11/516GasSolubilitycoefficientat37C(ml/dl/mmHg)Partialpressuregradient(mmHg)CO20.592X63.552O20.0244X621.5128CO2/O224.3X0.0972.35FactorsthatAffectGasDiffusionRateacrosstheFactorsthatAffectGasDiffusionRateacrosstheRespiratoryMembraneRespiratoryMembrane1.ThepartialpressuregradientbetweentwosidesofthemembraneDirectlyproportional2.Thediffusioncoefficientofthegas3.Thethicknessofrespiratorymembrane.4.Thesurfaceareaofrespiratorymembrane.Removeofthelung,e
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