资源描述：
《呼吸系统 气体交换(英文版).ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、RespiratorySystem(Ⅱ)GasExchangeAlveolar-BloodGasExchangeGasExchangeintheTissuesTransportinBloodThebloodthatentersthepulmonarycapillariesis,ofcourse,systemicvenousbloodpumpedtothelungsviathepulmonaryarteries.Havingcomefromthetissues,ithasarelativelyhighPCO2andare
2、lativelylowPO2.Thedifferencesinthepartialpressuresofoxygenandcarbondioxideonthetwosidesofthealveolar-capillarymembraneresultinthenetdiffusionofoxygenfromalveolitobloodandofcarbondioxidefrombloodtoalveoli.Asthisdiffusionoccurs,thecapillarybloodPO2risesanditsPCO2f
3、alls.Thenetdiffusionofthesegasesceaseswhenthecapillarypartialpressuresbecomeequaltothoseinthealveoli.Inanormalperson,therateatwhichoxygenandcarbondioxidediffusearesorapidandthebloodflowthroughthecapillariessoslowthatcompeteequilibriumisreachedwellbeforetheendoft
4、hecapillaries.Thus,thebloodthatleavesthepulmonarycapillariestoreturntotheheartandbepumpedintothesystemicarterieshasessentiallythesamePO2andPCO2asalveolarair.Inlungaffectionsorpulmonaryedema,someofthealveolimaybecomefilledwithfluid.Diffusionmayalsobeimpairedifthe
5、alveolarwallsbecomethickened.Veryimportantly,diffusionproblemsinthelungarerestrictedtooxygenanddonotaffecteliminationofcarbondioxide,whichismuchmorediffusiblethanoxygen.GasExchangeinthetissuesMetabolicreactionsoccurringwithincellsareconstantlyconsumingoxygenandp
6、roducingcarbondioxide.Therefore,intracellularPO2islowerandPCO2higherthaninblood.Astheresult,thereisanetdiffusionofoxygenfrombloodintocells,andanetdiffusionofcarbondioxidefromcellsintoblood.Inthismanner,asbloodflowsthroughsystemiccapillaries,itsPO2decreasesandits
7、PCO2increases.Transport---O2HemoglobinmoleculeEachironatomcanbindonemoleculeofoxygen,asinglehemoglobinmoleculecanbindfourmoleculesofoxygen.aproteinmadeupoffoursubunitsboundtogetherEachhemoglobinmoleculeisaproteinmadeupoffoursubunitsboundtogether.Eachsubunitconsi
8、stsofmoleculargroupknownashemeandapolypeptideattachedtotheheme.Eachofthefourhemegroupsinahemoglobinmoleculecontainsoneatomofiron,towhichoxygenbinds.Transport---CO2Ina
