ACIDBASE-BALANCE-Austin-Community-College-District：酸碱平衡奥斯汀社区学院区课件

Acid-BaseBalance:OverviewMLAB2401:ClinicalChemistry

KeriBrophy-MartinezTermsAcid Anysubstancethatcanyieldahydrogenion(H+)orhydroniumionwhendissolvedinwaterReleaseofprotonorH+BaseSubstancethatcanyieldhydroxylions(OH-)AcceptprotonsorH+

TermspK/pKaNegativelogoftheionizationconstantofanacidStrongacidswouldhaveapK<3StrongbasewouldhaveapK>9pHNegativelogofthehydrogenionconcentrationpH=pK+log([base]/[acid])RepresentsthehydrogenconcentrationTermsBufferCombinationofaweakacidand/oraweakbaseanditssaltWhatdoesitdo?ResistschangesinpHEffectivenessdependsonpKofbufferingsystempHofenvironmentinwhichitisplacedTermsAcidosispHlessthan7.35AlkalosispHgreaterthan7.45Note:NormalpHis7.35-7.45Acid-BaseBalanceFunctionMaintainspHhomeostasisMaintenanceofH+concentrationPotentialProblemsofAcid-BasebalanceIncreasedH+concentrationyieldsdecreasedpHDecreasedH+concentrationyieldsincreasedpHRegulationofpHDirectrelationoftheproductionandretentionofacidsandbasesSystemsRespiratoryCenterandLungsKidneysBuffersFoundinallbodyfluidsWeakacidsgoodbufferssincetheycantiltareactionintheotherdirectionStrongacidsarepoorbuffersbecausetheymakethesystemmoreacid8BloodBufferSystemsWhydoweneedthem?Iftheacidsproducedinthebodyfromthecatabolismoffoodandothercellularprocessesarenotremovedorbuffered,thebody’spHwoulddropSignificantdropsinpHinterfereswithcellenzymesystems.BloodBufferSystemsFourMajorBufferSystemsProteinBuffersystemsAminoacidsHemoglobinBuffersystemPhosphateBuffersystemBicarbonate-carbonicacidBuffersystemBloodBufferSystemsProteinBufferSystemOriginatesfromaminoacidsALBUMIN-primaryproteinduetohighconcentrationinplasmaBufferbothhydrogenionsandcarbondioxideBloodBufferingSystemsHemoglobinBufferSystemRolesBindsCO2

BindsandtransportshydrogenandoxygenParticipatesinthechlorideshiftMaintainsbloodpHashemoglobinchangesfromoxyhemoglobintodeoxyhemoglobinOxygenDissociationCurveCurveB:NormalcurveCurveA:Increasedaffinityforhgb,sooxygenkeepcloseCurveC:Decreasedaffinityforhgb,sooxygenreleasedtotissuesBohrEffectItallaboutoxygenaffinity!BloodBufferSystemsPhosphateBufferSystemHasamajorroleintheeliminationofH+viathekidneyAssistsintheexchangeofsodiumforhydrogenItparticipatesinthefollowingreactionHPO-24+H+H2PO–4EssentialwithintheerythrocytesBloodBufferSystemsBicarbonate/carbonicacidbuffersystemFunctionalmostinstantaneouslyCellsthatareutilizingO2,produceCO2,whichbuildsup.Thus,moreCO2isfoundinthetissuecellsthaninnearbybloodcells.Thisresultsinapressure(pCO2).Diffusionoccurs,theCO2leavesthetissuethroughtheinterstitialfluidintothecapillarybloodBicarbonate/CarbonicAcidBufferCarbonicacidBicarbonateConjugatebaseExcretedinurineExcretedbylungsBicarbonate/carbonicacidbuffersystem

HowisCO2transported?5-8%transportedindissolvedformAsmallamountoftheCO2combinesdirectlywiththehemoglobintoformcarbaminohemoglobin92-95%ofCO2willentertheRBC,andunderthefollowingreactionCO2+H20H++HCO3-Oncebicarbonateformed,exchangedforchlorideHenderson-HasselbalchEquationRelationshipbetweenpHandthebicarbonate-carbonicacidbuffersysteminplasmaAllowsustocalculatepHHenderson-HasselbalchEquationGeneralEquationpH=pK+logA-HABicarbonate/CarbonicAcidsystem pH=pK+logHCO3

H2CO3(PCO2x0.0301)

Henderson-HasselbalchEquationpH=pK+logHHAThepCO2andtheHCO3arereadorderivedfromthebloodgasanalyzer pCO2=40mmHg HCO3-=24mEq/LConvertthepCO2tomaketheunitsthesame pCO2=40mmHg*0.03=1.2mEq/LLetsdeterminethepH:PluginpKof6.1

PutthedataintheformulapH=pK+log24mEq/L1.2mEq/LpH=pK+log20pH=pK+1.30pH=6.1+1.30pH=7.40TheRatio….Normalis:20=Kidney =metabolic 1LungsrespiratoryTheratioofHCO3-(salt)toH2CO3(acid)isnormally20:1AllowsbloodpHof7.40ThepHfalls(acidosis)asbicarbonatedecreasesinrelationtocarbonicacidThepHrises(alkalosis)asbicarbonateincreasesinrelationtocarbonicacid

PhysiologicBufferSystemsLungs/respiratoryQuickestwaytorespond,takesminutestohourstocorrectpHEliminatevolatilerespiratoryacids suchasCO2Doesn’taffectfixedacidslikelacticacidBodypHcanbeadjustedbychangingrateanddepthofbreathing“blowingoff”ProvideO2tocellsandremoveCO2PhysiologicBufferSystemsKidney/MetabolicCaneliminatelargeamountsofacidCanexcretebaseaswellCantakeseveralhourstodaystocorrectpHMosteffectiveregulatorofpHIfkidneyfails,pHbalancefails25ReferencesBishop,M.,Fody,E.,&Schoeff,l.(2010).ClinicalChemistry:Techniques,principles,Correlations.Baltimore:WoltersKluwerLippincott