生理学双语课件-呼吸-2

第二节呼吸气体的交换一、气体交换原理（一）气体的扩散机体内的气体交换就是以扩散方式进行的。气体扩散速率受下列因素的影响：11．气体的分压差

在混合气体中，每种气体分子运动所产生的压力为各该气体的分压，它不受其它气体存在的影响，只决定于它自身的浓度。两个区域之间的分压差（△P）是气体扩散的动力，分压差大，扩散快。22.气体的分子量和溶解度扩散速率和该气体分子量（MW）的平方根成反比，与溶解度成正比。33．扩散面积和距离气体扩散速率与扩散面积（A）成正比。与扩散距离(d)成反比。4．温度

扩散速率与温度（T）成正比。4inwhichDisthediffusionrate,△Pisthepressuredifferencebetweenthetwoendsofthediffusionpathway,Aisthecross-sectionalareaofthepathway,Sisthesolubilityofthegas,disthedistanceofdiffusion,andMWisthemolecularweightofthegas.5Inadditiontothepressuredifference,severalotherfactorsaffecttherateofgasdiffusioninafluid.Theyare(1)thesolubilityofthegasinthefluid,(2)thecross-sectionalareaofthefluid,(3)thedistancethroughwhichthegasmustdiffuse,6(4)themolecularweightofthegas,and(5)thetemperatureofthefluid.Inthebody,thelastofthesefactors,thetemperature,remainsreasonablyconstantandusuallyneednotbeconsidered.7A.IntroductionGasescanmovefromonepointtoanotherbydiffusionandthatthecauseofthismovementisalwaysapres­suredifferencefromthefirstpointtothenext.Thus,oxygendiffusesfromthealveoliintothepulmonarycapillarybloodbecausetheoxygenpressure(PO2)inthealveoliisgreaterthanthePO2inthepulmonaryblood.8Then,inthetissues,ahigherPO2inthecapillarybloodthaninthetissuescausesoxygentodiffuseintothesurroundingcells.Conversely,whenoxygenismetabolizedinthecellstoformcarbondioxide,theintracellularcarbondioxidepressure(PCO2)risestoahighvalue,whichcausescarbondioxidetodiffuseintothetissuecapillaries.9Similarly,itdiffusesoutofthebloodintothealveolibecausethePCO2inthepulmonarycapillarybloodisgreaterthanthatinthealveoli.Basically,then,thetransportofoxygenandcarbondioxidebytheblooddependsonbothdiffusionandthemovementofblood.10呼吸膜{含表面活性物质的液体层肺泡上皮细胞层肺泡上皮细胞基膜层间隙毛细血管基膜层毛细血管内皮细胞层三、肺换气1112（二）影响肺换气的因素1、呼吸膜（1）厚度（2）面积2、通气/血流比值每分肺泡通气量和每分肺血流量之间的比值。为0.84。（V/Q)13

V/Qratioistheratioofalveolarventilation(V)topulmonarybloodflow(Q).MatchingventilationandperfusionisimportanttoachievetheidealexchangeofO2andCO2.Ifthefrequency,tidalvolume,andcardiacoutputarenormal,theV/Qratioisapproximately0.8.ThissituationresultsinanarterialPO2of100mmHgandanarterialPCO2of40mmHg.14如果VA/Q比值增大，这就意味着通气过剩，血流不足，部分肺泡气未能与血液气充分交换，致使肺泡无效腔增大。15反之，VA/Q下降，则意味着通气不足，血流过剩，部分血液流经通气不良的肺泡，未能得到充分更新,血就流回了心脏。犹如发生了功能性的动-静脉短路。16肺泡无效腔增大动静脉短路171.V/QratioinairwayobstructionIftheairwaysarecompletelyblocked(e.g.,byapieceofsteakcaughtinthetrachea),thenventilationiszero.Ifbloodflowisnormal,thenV/Qiszero.18Thereisnogasexchangeinalungthatisperfusedbutnotventilated.ThePO2andPCO2ofpulmonarycapillaryblood(and,therefore,ofsystemicarterialblood)willapproachtheirvaluesinmixedvenousblood.192.V/QratioinbloodflowobstructionIfbloodflowtoalungiscompletelyblocked(e.g.,byanembolismoccludingapulmonaryartery),thenbloodflowtothatlungiszero.Ifventilationisnormal,thenV/Qisinfinite.Thereisnogasexchangeinalungthatisventilatedbutnotperfused.20动脉静脉O2(30mmHg)CO2(50mmHg)O2(100mmHg)CO2(40mmHg)O2(40mmHg)CO2(46mmHg)组织细胞三、组织换气21DiffusionofOxygenfromthePeripheralCapillariesintotheTissueFluidWhenthearterialbloodreachestheperipheraltissues,itsPO2inthecapillariesisstill95mmHg.YetthePO2intheinterstitialfluidthatsurroundsthetissuecellsaveragesonly40mmHg.22Thus,thereisatremendousinitialpressuredifferencethatcausesoxygentodiffuserapidlyfromthebloodintothetissues,sorapidlythatthecapillaryPO2fallsalmosttoequalthe40mmHgpressureintheinterstitial.Therefore,thePO2ofthebloodleavingthetissuecapillariesandenteringtheveinsisalsoabout40mmHg.23Whenoxygenisusedbythecells,mostofitbecomescarbondioxide,andthisincreasestheintracellularPCO2BecauseofthehightissuecellPCO2,carbondioxidediffusesfromthecellsintothetissuecapillariesandisthencarriedbythebloodtothelungs.Inthelungs,itdiffusesfromthepulmonarycapillariesintothealveoli.Thus,ateachpointinthegastransportchain,carbondioxidediffusesinadirectionexactlyoppositethatofthediffusionofoxygen.24Yetthereisonemajordifferencebetweenthediffusionofcarbondioxideandthatofoxygen:carbondioxidecandiffuseabout20timesasrapidlyasoxygen.Therefore,thepressuredifferencesrequiredtocausecarbondioxidediffusionare,ineachinstance,farlessthanthepressuredifferencesrequired.25第三节气体在血液中的运输26一、氧和二氧化碳在血液中运输的基本形式（一）物理溶解比例小（二）化学结合主要O2溶解的O2化学结合的O2溶解的O2O2CO2溶解的CO2化学结合的CO2溶解的CO2

CO227二、氧的运输（一）物理溶解占血液总氧含量的约1.5%（二）化学结合占血液总氧含量的约98.5%与血红蛋白（Hb）进行化学结合28TransportOfOxygenInTheBloodNormally,about97percentoftheoxygentransportedfromthelungstothetissuesiscarriedinchemicalcombinationwithhemoglobinintheredbloodcells.Theremaining3percentistransportedinthedissolvedstateinthewateroftheplasmaandcells.Thus,undernormalconditions,oxygeniscarriedtothetissuesalmostentirelybyhemoglobin.291.

Hb的分子结构{1个珠蛋白4个血红素四条多肽链22每个血红素有4个吡咯环，其中心有一个Fe2+一条多肽链和一个血红素相连形成单体（亚单位）。30312.Hb与O2的结合特点（1）反应快，可逆，不需要酶的催化，受O2分压的影响。32（2）Fe2+与O2的结合是氧合，不是氧化。（3）1分子的Hb可以结合4分子的O2。33ReversibleCombinationofOxygenwithHemoglobinTheoxygenmoleculecombineslooselyandreversiblywiththehemeportionofthehemoglobin.WhenPO2ishigh,asinthepulmonarycapillaries,oxygenbindswiththehemoglobin,butwhenPO2islow,asinthetissuecapillaries,oxygenisreleasedfromthehemoglobin.Thisisthebasisforalmostalloxygentransportfromthelungstothetissues.34

A.HemoglobinCharacteristicsglobularproteinoffoursubunitsEachsubunitcontainsaheme,whichisiron-containingporphyrin.卟啉Theironisintheferrousstate(Fe2+),whichbindsO2,[Ifironisintheferricstate(Fe3+),itismethemoglobin高铁血红蛋白,whichdoesnotbindO2]35Eachsubunithasapolypeptidechain.Twoofthesubunitshaveαchainsandtwoofthesubunitshaveβchains;thus,normaladulthemoglobiniscalledα2β2.36

O2capacityisthemaximumamountofO2thatcanbeboundtohemoglobin.O2capacityisdeterminedbythehemoglobinconcentrationinblood.37O2capacitylimitstheamountofO2thatcanbecarriedinblood.O2capacityismeasuredat100%saturation.38O2contentO2contentisthetotalamountofO2carriedinblood,includingboundanddissolvedO2,dependsonthehemoglobinconcentrationandthePo2.39Saturationofthehemoglobin.thepercentageofhemoglobinboundwithoxygeniscalledthepercentsaturationofthehemoglobin.40100ml血液中，Hb所能结合的最大O2量称为氧容量。而实际结合的O2量称为氧含量。氧含量和氧容量的百分比为氧饱和度。41•HbO2呈鲜红色，去氧Hb呈紫蓝色。当表浅毛细血管血液中去氧Hb含量达5g/100ml血液以上时，皮肤、粘膜呈浅蓝色，称紫绀。423、氧离曲线（oxygendissociationcurve）是表示PO2与氧饱和度关系的曲线。呈S形。43上段：PO2100~60mmHg中段：PO260~40mmHg下段：PO240~15mmHg44上段PO2100~60mmHg：曲线平坦，受O2分压影响小。是Hb与O2的结合阶段。意义：当外环境或吸入气中的O2分压下降，造成血PO2降低时，仍能为机体摄取和携带足够的O2。45中段：PO260~40mmHg曲线较陡，是HbO2释放O2的部分。意义：当动脉血流经组织时，可释放出适量的O2，满足机体安静状态下对O2

的需求。46下段：PO240~15mmHg曲线很陡，表明当O2分压稍有下降时，血氧饱和度将明显降低。也是Hb与O2的解离阶段。意义：当动脉血流经活动增强的组织时，可释放足够的O2，满足活动增强组织对O2需求。471.HemoglobincombinesrapidlyandreversiblywithO2toformoxyhemoglobin. 2.Thehemoglobin-O2dissociationcurveisaplotofsaturationofhemoglobinasafunction函数ofPO2. a.AtaPO2of100mmHg(e.g.,arterialblood)hemoglobinisalmost100%saturated;O2isboundtoallfourhemegroupsonallhemoglobinmolecules.48ThePO2at50%saturationistheP50.Fiftypercentsaturationmeansthat,onaverage,twoofthefourhemegroupsofeachhemoglobinmoleculehaveO2bound.49ThesigmoidshapeofthecurveistheresultofachangeintheaffinityofhemoglobinaseachsuccessiveO2moleculebindstoahemesite(calledpositivecooperativity).BindingofthefirstO2moleculeincreasestheaffinityforthesecondO2molecule,andsoforth.50TheaffinityforthefourthO2moleculeisthehighest.ThischangeinaffinityfacilitatestheloadingofO2inthelungs(flatportionofthecurve)andtheunloadingofO2atthetissues(steepportionofthecurve).51

InthelungsAlveolargashasaPO2of100mmHg.Pulmonarycapillarybloodis"arterialized"bythediffusionofO2fromalveolargasintoblood,sothatthePO2ofpulmonarycapillarybloodalsobecomes100mmHg.52ThecurveisalmostflatwhenthePO2isbetween60mmHgand100mmHg.Thus,humanscantoleratechangesinatmosphericpressure(andPO2)withoutcompromiseoftheO2-carryjngcapacityofhemoglobin.53IntheperipheraltissuesO2diffusesfromarterialbloodtothecells.ThegradientforO2diffusionismaintainedbecausethecellsconsumeO2foraerobicmetabolism,keepingthetissuePO2low.Theloweraffinity-ofhemoglobinforO2inthissteepportionofthecurvefacilitatestheunloadingofO2tothetissues.544、影响氧离曲线的因素通常用P50表示Hb对O2的亲和力。P50是使Hb氧饱和度达50%时的PO2。P50增大，表明Hb对O2的亲和力降低，曲线右移；P50降低，说明Hb对O2的亲和力增加，曲线左移。5556（1）PCO2和pH的影响pH降低或PCO2升高，P50增大，曲线右移，促使O2的释放；反之相反。影响因素：5758波尔效应（Bohreffect)：当酸度增大时，Hb对氧的亲和力下降。当酸度减小时相反。59生理意义可促进肺毛细血管血液的氧合（因为CO2从血进入肺泡，酸度下降）。又有利于组织毛细血管血液氧气的释放（因为CO2从组织入血，酸度上升）。60（2）温度的影响

温度升高，氧离曲线右移，促使O2的释放；温度降低，曲线左移，不利于O2释放。61626364（3）2、3-二磷酸甘油酸（2、3-DPG)2,3-DPG浓度升高，氧离曲线右移：2,3-DPG浓度升降低，曲线左移。65AnumberoffactorscandisplacethedissociationcurveinonedirectionortheotherinthemannershowninFigurebelow.Thisfigureshowsthatwhenthebloodbecomesslightlyacidic,withthepHdecreasingfromthenormalvalueof7.4to7.2,theoxygen-hemoglobindissociationcurveshifts,onaverage,about15percenttotheright.66Conversely,anincreaseinthepHfromthenormal7.4to7.6shiftsthecurveasimilaramounttotheleft.67allofwhichshiftthecurvetotheright,are(1)increasedcarbondioxideconcentration,(2)increasedbloodtemperature,and(3)increased2,3-diphosphoglycerate(DPG),ametabolicallyimportantphosphatecompoundpresentinthebloodbutindifferentconcentrationsunderdifferentmetabolicconditions.68TheBohrEffect:IncreasesinPCO2orhydrogenions(decreasesinpH) shiftthecurvetotheright,decreasingtheaffinityofhemoglobinforO2andIncreasingDeliveryofOxygentotheTissuesO2).69Forexample,duringexercise,thetissuesproducemoreCO2,whichdecreasestissuepHand,throughtheBohreffect,stimulatesO2deliverytotheexercisingmuscle.70三、二氧化碳的运输（一）物理溶解每100ml静脉血，物理溶解的CO2约占总量的的5%。71（二）化学结合{碳酸氢盐氨基甲酸血红蛋白88%7%72Transportofcarbondioxidebythebloodisnotnearlysogreataproblemastransportofoxygen,becauseeveninthemostabnormalconditions,carbondioxidecanusuallybetransportedinfargreaterquantitiesthancanoxygen.73However,theamountofcarbondioxideintheblooddoeshavemuchtodowithacid-basebalanceofthebodyfluids.741.TransportofCarbonDioxideintheDissolvedStateTobegintheprocessofcarbondioxidetransport,carbondioxidediffusesoutofthetissuecellsinthedissolvedmolecularcarbondioxideform.Asmallportionofthecarbondioxideistransportedinthedissolvedstatetothelungs,onlyabout0.3milliliterofcarbondioxideistransportedintheformofdissolvedcarbondioxidebyeach100millilitersofblood.Thisisonlyabout7percentofallthecarbondioxidenormallytransported.75

碳酸氢盐红细胞内碳酸氢钾血浆内碳酸氢钠76TransportofCarbonDioxideintheFormofBicarbonateIonThedissolvedcarbondioxideinthebloodreactswithwatertoformcarbonicacid.Insidetheredbloodcarbonicanhydrase碳酸酐酶catalyzesthereactionbetweencarbondioxideandwater,thenthecarbonicacidformedintheredcells(H2CO3)dissociatesintohydrogenandbicarbonateions(H+andHCO3-).77Mostofthehydrogenionsthencombinewiththehemoglobinintheredbloodcells.Inturn,manyofthebicarbonateionsdiffusefromtheredcellsintotheplasmawhilechlorideionsdiffuseintotheredcellstotaketheirplace(thechlorideshift).78Thereversiblecombinationofcarbondioxidewithwaterintheredbloodcellsundertheinfluenceofcarbonicanhydraseaccountsforabout70percentofthecarbondioxidetransportedfromthetissuestothelungs.Thus,thismeansoftransportingcarbondioxideisbyfarthemostimportantofallthemethodsfortransport.792、HbNHCOOHHbNH2O2+H++CO2HbNHCOOH+O2肺组织80TransportofCarbonDioxideinCombinationwithHemoglobinandPlasmaProteins-Carbaminohemoglobin.Inadditiontoreactingwithwater,carbondioxidereactsdirectlywithamineradicalsofthehemoglobinmoleculetoformthecompoundcarbaminohemoglobin氨基甲酰血红蛋白

(CO2Hgb).81Thiscombinationofcarbondioxidewiththehemoglobinisareversiblereactionthatoccurswithaloosebond,sothatthecarbondioxideiseasilyreleasedintothealveoli,wherethePCO2islowerthaninthetissuecapillaries.82Thiscarbaminohemoglobinmechanismprovidestransportofabout20percentofthetotalquantityofcarbondioxide.83（三）CO2的解离曲线（carbondioxidedissociationcurve）表示血液中CO2含量与PCO2关系的曲线，几乎呈线形关系。8485ThecurveBELOWdepictsthisdependenceoftotalbloodcarbondioxideinallitsformsonPCO2;thiscurveiscalledthecarbondioxidedissociationcurve.86（四）Hb的结合对CO2运输的影响O2与Hb结合将促使CO2释放，这一效应称为

何尔登效应（Haldaneeffect)87TheHaldaneEffect:WhenOxygenBindswithHemoglobin,CarbonDioxideisReleasedtoIncreaseCO2Transport88Earlierinthechapter,itwaspointedoutthatanincreaseincarbondioxideinthebloodcausesoxygentobedisplacedfromthehemoglobin(theBohreffect)andthatthisisanimportantfactorinincreasingoxygentransport.89Thereverseisalsotrue:bindingofoxygenwithhemoglobintendstodisplacecarbondioxidefromtheblood.Indeed,thiseffect,calledtheHaldaneeffect,isquantitativelyfarmoreimportantinpromotingcarbondioxidetransportthanistheBohreffectinpromotingoxygentransport.90第四节呼吸运动的调节91一.呼吸中枢与呼吸节律的形成（一）呼吸中枢921、脊髓脊髓中支配呼吸肌的运动神经元位于第3-5颈段（支配膈肌）和胸段（支配肋间肌和腹肌等）前角。932、下位脑干

延髓和脑桥呼吸节律产生于低(下)位脑干。9495脑桥上部有呼吸调整中枢：相对集中于臂旁内侧核（NPBM)和KF核（合称PBKF核群）。其主要的作用是限制吸气，促使吸气转为呼气。96关于长吸中枢（脑桥中下部）目前趋于否定。973、高位脑脑桥以上部位特别是大脑皮层大脑皮层对呼吸的调节系统是通过躯体运动神经。。下位脑干的呼吸调节系统是自主节律呼吸调节系统.它们的下行通路是分开的。98Itisdividedintothreemajorcollectionsofneurons:1．Adorsalrespiratorygroup,locatedinthedorsalportionofthemedulla,whichmainlycausesinspiration;992.Aventralrespiratorygroup,locatedintheventrolateralpartofthemedulla,whichcancauseeitherexpirationorinspiration,dependingonwhichneuronsinthegrouparestimulated;1003Thepneumotaxiccenter呼吸调整中枢,locateddorsallyinthesuperiorportionofthepons,whichhelpscontroltherateandpatternofbreathing.Thedorsalrespiratorygroupofneuronsplaysthemostfundamentalroleinthecontrolofrespiration.101

NeuralControlofBreathingThenervoussystemnormallyadjuststherateofalveolarventilationalmostexactlytothedemandsofthebodysothattheoxygenpressure(PO2)andcarbondioxidepressure(PCO2)inthearterialbloodarehardlyalteredevenduringexerciseandmostothertypesofrespiratorystress.102CentralcontrolofbreathingRespiratoryCenterTherespiratorycenteriscomposedofseveralgroupsofneuronslocatedbilaterallyinthemedullaoblongataandpons,asshownforonesideinFigurebelow.103Cerebralcortex Breathingcanbeundervoluntarycontrol;therefore,apersoncanvoluntarilyhyperventilateorhypoventilate.104二、呼吸的反射性调节肺牵张反射（黑-伯反射）(Hering-Breuerreflex)1051、肺扩张反射是肺充气或肺扩张引起的吸气抑制。感受器位于气管到支气管的平滑肌中。

肺扩张肺牵张感受器兴奋————呼吸中枢吸气停止，引起呼气。迷走神经106意义：防止吸气过深，促进吸气向呼气转化，调节呼吸频率和深度。1072、肺缩小反射肺缩小或肺萎陷引起的吸气反射。肺缩小肺泡及细支气管牵张感受器迷走神经呼吸中枢呼气停止，转为吸气108TheHering-BreuerInflationReflexStretchreceptorsarelocatedinthemuscularportionsofthewallsofthebronchiandbronchiolesthroughoutthelungs.theytransmitsensorynervesignalsthroughthevagiintothedorsalrespiratorygroupofneuronswhenthelungsbecomeoverstretched.109Thesesignalsaf­fectinspirationinmuchthesamewayassignalsfromthepneumotaxiccenter;thatis,whenthelungsbecomeoverlyinflated,thestretchreceptorsactivateanappropriatefeedbackresponsethat"switchesoff"theinspiratoryprocessandthusstopsfurtherinspiration.ThisiscalledtheHering-Breuerinflationreflex.Thisreflexalsoincreasestherateofrespiration,thesameasistrueforsignalsfromthepneumotaxiccenter.110三、呼吸的化学反射性调节（一）化学感受器1、外周化学感受器

111颈动脉体和主动脉体：对PO2降低，PCO2升高及pH下降敏感,受到刺激，反射性地引起呼吸加深加快。112

2、中枢化学感受器位于延髓腹外侧，其有效刺激是脑脊液和局部细胞外液的H+，不感受局部CO2血氢离子和缺O2的刺激。113（二）CO2对呼吸的影响

一定水平的PCO2对维持呼吸和呼吸中枢的兴奋性是必要的，CO2是调节呼吸的最重要的生理性体液因子。114吸入气CO24%肺通气量增加1倍吸入气CO27%CO2

麻醉现象115CO2刺激呼吸是通过两条途径实现的，一是通过刺激中枢化学感受器,二是刺激外周化学感受器反射性地使呼吸加深、加快。但两条途径中前者是主要的。116血液中的CO2能迅速通过血脑屏障，使化学感受器周围液体中的[H+]升高，从而刺激中枢化学感受器，再引起呼吸中枢的兴奋。117PCO2{外周化学感受器（20%）中枢化学感受器（80%）呼吸中枢呼吸加深，加快118119H+对呼吸的调节也是通过外周化学感受器和中枢化学感受器实现的,以前者为主。H+通过血液屏障的速度慢，限制了它对中枢化学感受器的作用。（三）H+对呼吸的影响120pH外周化学感受器呼吸中枢呼吸加深，加快121低O2对呼吸的刺激作用完全是通过外周化学感受器实现的。122当缺氧不甚严重时，低O2对中枢的直接作用是压抑。低O2可以通过对外周化学感受器的刺激而兴奋呼吸中枢以对抗低O2的直接压抑作用。123不过在严重低O2时，外周化学感受性反射已不足以克服低O2对中枢的压抑作用，终将导致呼吸障碍。124（四）低O2对呼吸的影响PO2外周化学感受器呼吸中枢+-当40mmHg≤PO2≤80mmHg呼吸加深加快

当PO2≤40mmHg呼吸抑制125CHEMICALCONTROLOFRESPIRATIONTheultimategoalofrespirationistomaintainproperconcentrationsofoxygen,carbondioxide,andhydrogenionsinthetissues.Itisfortunate,therefore,thatrespiratoryactivityishighlyresponsivetochangesineachofthese.126Excesscarbondioxideorexcesshydrogenionsinthebloodmainlyactdirectlyontherespiratorycenteritself,causinggreatlyincreasedstrengthofboththeinspiratoryandtheexpiratorymotorsignalstotherespiratorymuscles.127Oxygen,incontrast,doesnothaveasignificantdirecteffectontherespiratorycenterofthebrainincontrollingrespiration.Instead,itactsalmostentirelyonperipheralchemoreceptorslocatedinthecarotidandaorticbodies,andtheseinturntransmitappropriatenervoussignalstotherespiratorycenterforcontrolofrespiration.128

ChemoreceptorsforCO2,H+,andO21.Centralchemoreceptorsinthemedullaasensitivech