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1、PathogenicMechanismofPulmonaryHypertensionRoleofCa2+andIonChannelsandNOCertainproblemsrelatedtodistributionofbloodflowandotherhemodynamicsarespecialtothepulmonarycirculationandareespeciallyimportantforgasex-changeinthelungs.Thepresentdiscussionisconcerneds
2、peciallywiththesespecialfeaturesofthepulmonarycircu1ationPHYSIOLOGICANATOMYOFTHEPULMONARYCIRCULATORYSYSTEMPulmonaryvesselsThepulmonaryarteryextendsonly5centimetersbeyondtheapexoftherightventricleandthendividesintotherightandleftmainbranches,whichsupplybloo
3、dtothetworespectivelungs.Thepulmonaryarteryisalsothin,withawallthicknessabouttwicethatofthevenaecavaeandonethirdthatoftheaorta.Thepulmonaryarterialbranchesareveryshort,andallthepulmonaryateries,eventhesmallerarteriesandarterioles,havelargerdiametersthanthe
4、ircounterpartsystemicarteries.This,combinedwiththefactthatthevesselsareverythinanddistensible,givesthepulmonaryarterialtreealargecompliance,averagingalmost7ml/mmHg,whichissimilartothatoftheentiresystemicarterialtree.Thislargecomplianceallowsthepulmonaryart
5、eriestoaccommodateabouttwothirdsofthestrokevolumeoutputoftherightventricle.Thepulmonaryveins,likethepulmonaryarteries,areshort,buttheirdistensibilitycharacteristicsaresimilartothoseoftheveinsinthesystemiccirculationBronchialVesselsBloodalsoflowstothelungst
6、hroughsmallbronchialarteriesthatoriginatefromthesystemiccirculation,amountingtoaboutlto2percentofthetotalcardiacoutput.Thisbronchialarterialbloodisoxygenatedblood,incontrasttothepartiallydeoxygenatedbloodinthepulmonaryarteries.Itsuppliesthesupportingtssues
7、ofthelungs,includingtheconnectivetissue,septa,andlargeandsmallbronchi.PRESSURESINTHEPULMONARYSYSTEMPulmonaryarterialpressureaveragesabout25mmHginthenormalhumanbeing;thediastolicpulmonaryarterialpressure,about8mmHg;andthemeanpulmonaryarterialpressure,15mmHg
8、.PulmonaryarterialpressurePulmonaryCapillaryPressureThemeanpulmonarycapillarypressure,hasbeenestimatedbyindirectmeanstobeabout7mmHg.Theimportanceofthislowcapillarypressureisrelatedtofluidexchangefunctionsofth
