acid base balance ii—renal - raymond cheong：酸碱平衡二肾-雷蒙德昌

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1、AcidBaseBalanceII—RenalI.Introa.TypicalAmericanDiet—produces15,000mmolCO2perdayi.Renalexcretionofacid!b.VegetarianDiet—producesalkalineurineb/cofexcess“ash”indietc.Definitionsi.Acid—protondonorii.Base—protonacceptoriii.Strongacid—fullydissociatesintoH+&A

2、-atphysiologicalpHiv.Weakacid—doesn’tfullydissociate=>kidneycanrecombineintoHAv.TitratableAcid—conjugatebaseofweakacidthatactsasbufferinurinevi.Titratableacidity—amountofNaOHthatmustbeaddedtoa24hr.collectionofurinetotitratepHfrom7.4to4.5;measureoftheamou

3、ntofacidexcretedbykidneyinformofweakacidd.KidneyFunctioni.HCO3-reabsorption(~90%of4300mEq/dayHCO3reabsorbed)ii.RemovesexcessacidvianetH+excretionintheformoftitratableacid&ammonium=>generationofmoreHCO3-(~100mEq/daynewHCO3-)iii.NetHCO3-excretionfollowingc

4、onsumptionofexcessbase(baseload)II.AcidProducingDieta.Bodybuffersminimize↓pHdueto↑H+;kidneysrecycleHCO3&excreteH+b.TubularAcidificationi.90%ofHCO3(4300mEq/day)absorbedinPCT=>slight↓pHii.lowestpHoccursincollectingducts,whereH+isactivelysecretediii.minpH=4

5、.5-5.0iv.excessH+secretedasweakacids(titrated)andammoniumc.BicarbonateReabsorptioni.EarlyProximalTubule—highcapacity,reabsorbsmostfilteredHCO31.HCO3fromlumenmovesintocells;ICcarbonicanhydraseconvertsCO2↔H++HCO3a.H+secretedtotubulelumenb.HCO3reabsorbedw/N

6、a+w/ochangingluminalpHii.LateProximalTubule—highcapacity,generatesnewbicarbonate1.CO2frombloodmovesintocells,wherecarbonicanhydrasebreaksitdown=>NEWHCO3!!a.H+secretedtotubulelumen,whereitcombinesw/weakacids(AW-)=>HAWb.HCO3reabsorbedw/Na+2.smalldropinlumi

7、nalpH:7.4→6.8iii.CollectingDuct—lowcapacity,butcangeneratelargepHgradients1.protonpumpssecreteH+intolumen2.largedropinluminalpH:6.8→4.53.CO2frombloodcontinuestomoveintocells,wherecarbonicanhydrasebreaksitdown=>NEWHCO3!!tobloodstreamd.Ammonia(NH4+)3i.Stro

8、ngacidsarebrokendownandexcretedasammonia(NH4+)andA-NH3+H+↔NH4+1.NH3readilydiffusesthrucellmembranes,NH4+islesspermeable2.Ammoniageneratedfromglutaminebreakdowninmitochondria;alsogeneratesa-ketogluterate=>newHCO3production!