医学circulation1-heart as a pump-lw

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1、TheHeartasaPumpConductingsystemoftheheart.Excitation-contractioncouplingincardiacmuscleCa2+CharacteristicsoftheheartmusclecontractionDependingonconcentrationofextracelluarCa2+DiffusionofextracellarCa2+intosarcoplasm(mainsource)SarcoplasmicreticulumreleaseofCa2+ExtracellularCa2+stre

2、ngthofcontractionSarcoplasmicreticulumislesswelldevelopedanddoesnotstoreenoughCa2+.2.CardiacmuscleasasyncytiumatrialsyncytiumandventricularsyncytiumAPspreadsimmediatelytowholeatriumorventricleentireatriumorventriclecontractsalmostsimultaneouslygapjunction:verypermeabletoionsThestru

3、ctureofgapjunctions.Gapjunctionsarewater-filledchannelsthroughwhichionscanpassfromonecelltoanother.Thispermitsimpulsestobeconducteddirectlyfromonecelltoanother.CardiacPumpFunctioncardiaccycle:Thecardiaceventsoccurringfromthebeginningoftheoneheartbeattothebeginningofthenextarecalled

4、thecardiaccycle.Heartbeat:60-100/minTimeofCardiaccycle:0.8second(75/min)cardiaccyclesystolediastolesystole:periodofcontractionejectiondiastole:periodofrelaxationfillingSystolePeriod

5、e↓HR↓→diastole↑↑,systole↑HRcardiaccycle(s)systolediastole1.50.81500.40.300.500.250.151.150.35FunctionoftheventriclesaspumpscontractionorrelaxationpressurechangesopeningorclosingofvalvesejectionorfillingvolumechangesofventricleMECHANICALEVENTSOFTHECARDIACCYCLEAtrialsystoleVentricula

6、rsystole＊Isovolumicventricularcontraction＊VentricularejectionVentriculardiastole＊Isovolumicventricularrelaxation＊VentricularfillingAtrialsystole(a“primer”pump)AtriumcontractsVentriclerelaxedAtriumpressureincreases(Ap>Vp，Aop>Vp)A-VvalveopensSemilunarvalveclosedBloodflowfromatriumtov

7、entricleA-VvalvesemilunarvalveAp:AtriumpressureVp:VentricularpressureAop:AorticpressureContractionofatriumincreasesfillingofventricle(25%).Thisphaselastsabout0.1s.semilunarvalveA-VvalveA-VvalvesemilunarvalveVentricularsystole0.3sintraventricularpressuresemilunarvalveopensventriclee

8、jectsbloodventriclecontrac