生理學(xué)雙語課件-呼吸-2

第二節(jié)呼吸氣體的交換一、氣體交換原理（一）氣體的擴散機體內(nèi)的氣體交換就是以擴散方式進行的。氣體擴散速率受下列因素的影響：11．氣體的分壓差

在混合氣體中，每種氣體分子運動所產(chǎn)生的壓力為各該氣體的分壓，它不受其它氣體存在的影響，只決定于它自身的濃度。兩個區(qū)域之間的分壓差（△P）是氣體擴散的動力，分壓差大，擴散快。22.氣體的分子量和溶解度擴散速率和該氣體分子量（MW）的平方根成反比，與溶解度成正比。33．?dāng)U散面積和距離氣體擴散速率與擴散面積（A）成正比。與擴散距離(d)成反比。4．溫度

擴散速率與溫度（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.IntroductionGasescanmovefromonepointtoanotherbydiffusionandthatthecauseofthismovementisalwaysapres-suredifferencefromthefirstpointtothenext.Thus,oxygendiffusesfromthealveoliintothepulmonarycapillarybloodbecausetheoxygenpressure(PO2)inthealveoliisgreaterthanthePO2inthepulmonaryblood.8Then,inthetissues,ahigherPO2inthecapillarybloodthaninthetissuescausesoxygentodiffuseintothesurroundingcells.Conversely,whenoxygenismetabolizedinthecellstoformcarbondioxide,theintracellularcarbondioxidepressure(PCO2)risestoahighvalue,whichcausescarbondioxidetodiffuseintothetissuecapillaries.9Similarly,itdiffusesoutofthebloodintothealveolibecausethePCO2inthepulmonarycapillarybloodisgreaterthanthatinthealveoli.Basically,then,thetransportofoxygenandcarbondioxidebytheblooddependsonbothdiffusionandthemovementofblood.10呼吸膜{含表面活性物質(zhì)的液體層肺泡上皮細(xì)胞層肺泡上皮細(xì)胞基膜層間隙毛細(xì)血管基膜層毛細(xì)血管內(nèi)皮細(xì)胞層三、肺換氣1112（二）影響肺換氣的因素1、呼吸膜（1）厚度（2）面積2、通氣/血流比值每分肺泡通氣量和每分肺血流量之間的比值。為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，這就意味著通氣過剩，血流不足，部分肺泡氣未能與血液氣充分交換，致使肺泡無效腔增大。15反之，VA/Q下降，則意味著通氣不足，血流過剩，部分血液流經(jīng)通氣不良的肺泡，未能得到充分更新,血就流回了心臟。猶如發(fā)生了功能性的動-靜脈短路。16肺泡無效腔增大動靜脈短路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動脈靜脈O2(30mmHg)CO2(50mmHg)O2(100mmHg)CO2(40mmHg)O2(40mmHg)CO2(46mmHg)組織細(xì)胞三、組織換氣21DiffusionofOxygenfromthePeripheralCapillariesintotheTissueFluidWhenthearterialbloodreachestheperipheraltissues,itsPO2inthecapillariesisstill95mmHg.YetthePO2intheinterstitialfluidthatsurroundsthetissuecellsaveragesonly40mmHg.22Thus,thereisatremendousinitialpressuredifferencethatcausesoxygentodiffuserapidlyfromthebloodintothetissues,sorapidlythatthecapillaryPO2fallsalmosttoequalthe40mmHgpressureintheinterstitial.Therefore,thePO2ofthebloodleavingthetissuecapillariesandenteringtheveinsisalsoabout40mmHg.23Whenoxygenisusedbythecells,mostofitbecomescarbondioxide,andthisincreasestheintracellularPCO2BecauseofthehightissuecellPCO2,carbondioxidediffusesfromthecellsintothetissuecapillariesandisthencarriedbythebloodtothelungs.Inthelungs,itdiffusesfromthepulmonarycapillariesintothealveoli.Thus,ateachpointinthegastransportchain,carbondioxidediffusesinadirectionexactlyoppositethatofthediffusionofoxygen.24Yetthereisonemajordifferencebetweenthediffusionofcarbondioxideandthatofoxygen:carbondioxidecandiffuseabout20timesasrapidlyasoxygen.Therefore,thepressuredifferencesrequiredtocausecarbondioxidediffusionare,ineachinstance,farlessthanthepressuredifferencesrequired.25第三節(jié)氣體在血液中的運輸26一、氧和二氧化碳在血液中運輸?shù)幕拘问剑ㄒ唬┪锢砣芙獗壤。ǘ┗瘜W(xué)結(jié)合主要O2溶解的O2化學(xué)結(jié)合的O2溶解的O2O2CO2溶解的CO2化學(xué)結(jié)合的CO2溶解的CO2

CO227二、氧的運輸（一）物理溶解占血液總氧含量的約1.5%（二）化學(xué)結(jié)合占血液總氧含量的約98.5%與血紅蛋白（Hb）進行化學(xué)結(jié)合28TransportOfOxygenInTheBloodNormally,about97percentoftheoxygentransportedfromthelungstothetissuesiscarriedinchemicalcombinationwithhemoglobinintheredbloodcells.Theremaining3percentistransportedinthedissolvedstateinthewateroftheplasmaandcells.Thus,undernormalconditions,oxygeniscarriedtothetissuesalmostentirelybyhemoglobin.291.

Hb的分子結(jié)構(gòu){1個珠蛋白4個血紅素四條多肽鏈22每個血紅素有4個吡咯環(huán)，其中心有一個Fe2+一條多肽鏈和一個血紅素相連形成單體（亞單位）。30312.Hb與O2的結(jié)合特點（1）反應(yīng)快，可逆，不需要酶的催化，受O2分壓的影響。32（2）Fe2+與O2的結(jié)合是氧合，不是氧化。（3）1分子的Hb可以結(jié)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高鐵血紅蛋白,whichdoesnotbindO2]35Eachsubunithasapolypeptidechain.Twoofthesubunitshaveαchainsandtwoofthesubunitshaveβchains;thus,normaladulthemoglobiniscalledα2β2.36

O2capacityisthemaximumamountofO2thatcanbeboundtohemoglobin.O2capacityisdeterminedbythehemoglobinconcentrationinblood.37O2capacitylimitstheamountofO2thatcanbecarriedinblood.O2capacityismeasuredat100%saturation.38O2contentO2contentisthetotalamountofO2carriedinblood,includingboundanddissolvedO2,dependsonthehemoglobinconcentrationandthePo2.39Saturationofthehemoglobin.thepercentageofhemoglobinboundwithoxygeniscalledthepercentsaturationofthehemoglobin.40100ml血液中，Hb所能結(jié)合的最大O2量稱為氧容量。而實際結(jié)合的O2量稱為氧含量。氧含量和氧容量的百分比為氧飽和度。41?HbO2呈鮮紅色，去氧Hb呈紫藍色。當(dāng)表淺毛細(xì)血管血液中去氧Hb含量達5g/100ml血液以上時，皮膚、粘膜呈淺藍色，稱紫紺。423、氧離曲線（oxygendissociationcurve）是表示PO2與氧飽和度關(guān)系的曲線。呈S形。43上段：PO2100~60mmHg中段：PO260~40mmHg下段：PO240~15mmHg44上段PO2100~60mmHg：曲線平坦，受O2分壓影響小。是Hb與O2的結(jié)合階段。意義：當(dāng)外環(huán)境或吸入氣中的O2分壓下降，造成血PO2降低時，仍能為機體攝取和攜帶足夠的O2。45中段：PO260~40mmHg曲線較陡，是HbO2釋放O2的部分。意義：當(dāng)動脈血流經(jīng)組織時，可釋放出適量的O2，滿足機體安靜狀態(tài)下對O2

的需求。46下段：PO240~15mmHg曲線很陡，表明當(dāng)O2分壓稍有下降時，血氧飽和度將明顯降低。也是Hb與O2的解離階段。意義：當(dāng)動脈血流經(jīng)活動增強的組織時，可釋放足夠的O2，滿足活動增強組織對O2需求。471.HemoglobincombinesrapidlyandreversiblywithO2toformoxyhemoglobin. 2.Thehemoglobin-O2dissociationcurveisaplotofsaturationofhemoglobinasafunction函數(shù)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、影響氧離曲線的因素通常用P50表示Hb對O2的親和力。P50是使Hb氧飽和度達50%時的PO2。P50增大，表明Hb對O2的親和力降低，曲線右移；P50降低，說明Hb對O2的親和力增加，曲線左移。5556（1）PCO2和pH的影響pH降低或PCO2升高，P50增大，曲線右移，促使O2的釋放；反之相反。影響因素：5758波爾效應(yīng)（Bohreffect)：當(dāng)酸度增大時，Hb對氧的親和力下降。當(dāng)酸度減小時相反。59生理意義可促進肺毛細(xì)血管血液的氧合（因為CO2從血進入肺泡，酸度下降）。又有利于組織毛細(xì)血管血液氧氣的釋放（因為CO2從組織入血，酸度上升）。60（2）溫度的影響

溫度升高，氧離曲線右移，促使O2的釋放；溫度降低，曲線左移，不利于O2釋放。61626364（3）2、3-二磷酸甘油酸（2、3-DPG)2,3-DPG濃度升高，氧離曲線右移：2,3-DPG濃度升降低，曲線左移。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、二氧化碳的運輸（一）物理溶解每100ml靜脈血，物理溶解的CO2約占總量的的5%。71（二）化學(xué)結(jié)合{碳酸氫鹽氨基甲酸血紅蛋白88%7%72Transportofcarbondioxidebythebloodisnotnearlysogreataproblemastransportofoxygen,becauseeveninthemostabnormalconditions,carbondioxidecanusuallybetransportedinfargreaterquantitiesthancanoxygen.73However,theamountofcarbondioxideintheblooddoeshavemuchtodowithacid-basebalanceofthebodyfluids.741.TransportofCarbonDioxideintheDissolvedStateTobegintheprocessofcarbondioxidetransport,carbondioxidediffusesoutofthetissuecellsinthedissolvedmolecularcarbondioxideform.Asmallportionofthecarbondioxideistransportedinthedissolvedstatetothelungs,onlyabout0.3milliliterofcarbondioxideistransportedintheformofdissolvedcarbondioxidebyeach100millilitersofblood.Thisisonlyabout7percentofallthecarbondioxidenormallytransported.75

碳酸氫鹽紅細(xì)胞內(nèi)碳酸氫鉀血漿內(nèi)碳酸氫鈉76TransportofCarbonDioxideintheFormofBicarbonateIonThedissolvedcarbondioxideinthebloodreactswithwatertoformcarbonicacid.Insidetheredbloodcarbonicanhydrase碳酸酐酶catalyzesthereactionbetweencarbondioxideandwater,thenthecarbonicacidformedintheredcells(H2CO3)dissociatesintohydrogenandbicarbonateions(H+andHCO3-).77Mostofthehydrogenionsthencombinewiththehemoglobinintheredbloodcells.Inturn,manyofthebicarbonateionsdiffusefromtheredcellsintotheplasmawhilechlorideionsdiffuseintotheredcellstotaketheirplace(thechlorideshift).78Thereversiblecombinationofcarbondioxidewithwaterintheredbloodcellsundertheinfluenceofcarbonicanhydraseaccountsforabout70percentofthecarbondioxidetransportedfromthetissuestothelungs.Thus,thismeansoftransportingcarbondioxideisbyfarthemostimportantofallthemethodsfortransport.792、HbNHCOOHHbNH2O2+H++CO2HbNHCOOH+O2肺組織80TransportofCarbonDioxideinCombinationwithHemoglobinandPlasmaProteins-Carbaminohemoglobin.Inadditiontoreactingwithwater,carbondioxidereactsdirectlywithamineradicalsofthehemoglobinmoleculetoformthecompoundcarbaminohemoglobin氨基甲酰血紅蛋白

(CO2Hgb).81Thiscombinationofcarbondioxidewiththehemoglobinisareversiblereactionthatoccurswithaloosebond,sothatthecarbondioxideiseasilyreleasedintothealveoli,wherethePCO2islowerthaninthetissuecapillaries.82Thiscarbaminohemoglobinmechanismprovidestransportofabout20percentofthetotalquantityofcarbondioxide.83（三）CO2的解離曲線（carbondioxidedissociationcurve）表示血液中CO2含量與PCO2關(guān)系的曲線，幾乎呈線形關(guān)系。8485ThecurveBELOWdepictsthisdependenceoftotalbloodcarbondioxideinallitsformsonPCO2;thiscurveiscalledthecarbondioxidedissociationcurve.86（四）Hb的結(jié)合對CO2運輸?shù)挠绊慜2與Hb結(jié)合將促使CO2釋放，這一效應(yīng)稱為

何爾登效應(yīng)（Haldaneeffect)87TheHaldaneEffect:WhenOxygenBindswithHemoglobin,CarbonDioxideisReleasedtoIncreaseCO2Transport88Earlierinthechapter,itwaspointedoutthatanincreaseincarbondioxideinthebloodcausesoxygentobedisplacedfromthehemoglobin(theBohreffect)andthatthisisanimportantfactorinincreasingoxygentransport.89Thereverseisalsotrue:bindingofoxygenwithhemoglobintendstodisplacecarbondioxidefromtheblood.Indeed,thiseffect,calledtheHaldaneeffect,isquantitativelyfarmoreimportantinpromotingcarbondioxidetransportthanistheBohreffectinpromotingoxygentransport.90第四節(jié)呼吸運動的調(diào)節(jié)91一.呼吸中樞與呼吸節(jié)律的形成（一）呼吸中樞921、脊髓脊髓中支配呼吸肌的運動神經(jīng)元位于第3-5頸段（支配膈?。┖托囟危ㄖ淅唛g肌和腹肌等）前角。932、下位腦干

延髓和腦橋呼吸節(jié)律產(chǎn)生于低(下)位腦干。9495腦橋上部有呼吸調(diào)整中樞：相對集中于臂旁內(nèi)側(cè)核（NPBM)和KF核（合稱PBKF核群）。其主要的作用是限制吸氣，促使吸氣轉(zhuǎn)為呼氣。96關(guān)于長吸中樞（腦橋中下部）目前趨于否定。973、高位腦腦橋以上部位特別是大腦皮層大腦皮層對呼吸的調(diào)節(jié)系統(tǒng)是通過軀體運動神經(jīng)。。下位腦干的呼吸調(diào)節(jié)系統(tǒng)是自主節(jié)律呼吸調(diào)節(jié)系統(tǒng).它們的下行通路是分開的。98Itisdividedintothreemajorcollectionsofneurons:1．Adorsalrespiratorygroup,locatedinthedorsalportionofthemedulla,whichmainlycausesinspiration;992.Aventralrespiratorygroup,locatedintheventrolateralpartofthemedulla,whichcancauseeitherexpirationorinspiration,dependingonwhichneuronsinthegrouparestimulated;1003Thepneumotaxiccenter呼吸調(diào)整中樞,locateddorsallyinthesuperiorportionofthepons,whichhelpscontroltherateandpatternofbreathing.Thedorsalrespiratorygroupofneuronsplaysthemostfundamentalroleinthecontrolofrespiration.101

NeuralControlofBreathingThenervoussystemnormallyadjuststherateofalveolarventilationalmostexactlytothedemandsofthebodysothattheoxygenpressure(PO2)andcarbondioxidepressure(PCO2)inthearterialbloodarehardlyalteredevenduringexerciseandmostothertypesofrespiratorystress.102CentralcontrolofbreathingRespiratoryCenterTherespiratorycenteriscomposedofseveralgroupsofneuronslocatedbilaterallyinthemedullaoblongataandpons,asshownforonesideinFigurebelow.103Cerebralcortex Breathingcanbeundervoluntarycontrol;therefore,apersoncanvoluntarilyhyperventilateorhypoventilate.104二、呼吸的反射性調(diào)節(jié)肺牽張反射（黑-伯反射）(Hering-Breuerreflex)1051、肺擴張反射是肺充氣或肺擴張引起的吸氣抑制。感受器位于氣管到支氣管的平滑肌中。

肺擴張肺牽張感受器興奮————呼吸中樞吸氣停止，引起呼氣。迷走神經(jīng)106意義：防止吸氣過深，促進吸氣向呼氣轉(zhuǎn)化，調(diào)節(jié)呼吸頻率和深度。1072、肺縮小反射肺縮小或肺萎陷引起的吸氣反射。肺縮小肺泡及細(xì)支氣管牽張感受器迷走神經(jīng)呼吸中樞呼氣停止，轉(zhuǎn)為吸氣108TheHering-BreuerInflationReflexStretchreceptorsarelocatedinthemuscularportionsofthewallsofthebronchiandbronchiolesthroughoutthelungs.theytransmitsensorynervesignalsthroughthevagiintothedorsalrespiratorygroupofneuronswhenthelungsbecomeoverstretched.109Thesesignalsaf-fectinspirationinmuchthesamewayassignalsfromthepneumotaxiccenter;thatis,whenthelungsbecomeoverlyinflated,thestretchreceptorsactivateanappropriatefeedbackresponsethat"switchesoff"theinspiratoryprocessandthusstopsfurtherinspiration.ThisiscalledtheHering-Breuerinflationreflex.Thisreflexalsoincreasestherateofrespiration,thesameasistrueforsignalsfromthepneumotaxiccenter.110三、呼吸的化學(xué)反射性調(diào)節(jié)（一）化學(xué)感受器1、外周化學(xué)感受器

111頸動脈體和主動脈體：對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、中樞化學(xué)感受器位于延髓腹外側(cè)，其有效刺激是腦脊液和局部細(xì)胞外液的H+，不感受局部CO2血氫離子和缺O(jiān)2的刺激。113（二）CO2對呼吸的影響

一定水平的PCO2對維持呼吸和呼吸中樞的興奮性是必要的，CO2是調(diào)節(jié)呼吸的最重要的生理性體液因子。114吸入氣CO24%肺通氣量增加1倍吸入氣CO27%CO2

麻醉現(xiàn)象115CO2刺激呼吸是通過兩條途徑實現(xiàn)的，一是通過刺激中樞化學(xué)感受器,二是刺激外周化學(xué)感受器反射性地使呼吸加深、加快。但兩條途徑中前者是主要的。116血液中的CO2能迅速通過血腦屏障，使化學(xué)感受器周圍液體中的[H+]升高，從而刺激中樞化學(xué)感受器，再引起呼吸中樞的興奮。117PCO2{外周化學(xué)感受器（20%）中樞化學(xué)感受器（80%）呼吸中樞呼吸加深，加快118119H+對呼吸的調(diào)節(jié)也是通過外周化學(xué)感受器和中樞化學(xué)感受器實現(xiàn)的,以前者為主。H+通過血液屏障的速度慢，限制了它對中樞化學(xué)感受器的作用。（三）H+對呼吸的影響120pH外周化學(xué)感受器呼吸中樞呼吸加深，加快121低O2對呼吸的刺激作用完全是通過外周化學(xué)感受器實現(xiàn)的。122當(dāng)缺氧不甚嚴(yán)重時，低O2對中樞的直接作用是壓抑。低O2可以通過對外周化學(xué)感受器的刺激而興奮呼吸中樞以對抗低O2的直接壓抑作用。123不過在嚴(yán)重低O2時，外周化學(xué)感受性反射已不足以克服低O2對中樞的壓抑作用，終將導(dǎo)致呼吸障礙。124（四）低O2對呼吸的影響PO2外周化學(xué)感受器呼吸中樞+-當(dāng)40mmHg≤PO2≤80mmHg呼吸加深加快

當(dāng)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