CHAPTER 116 Disorders of Sodium and Water Homeostasis

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1、CHAPTER116 DisorDersofsoDiumanDWaterHomeostasis741Intracellular116 Water(2/3)ExtracellularWater(1/3)Interstitial(2/3)Blood(1/3)DISORDERSOFSODIUMAND25Na140150K4.5WATERHOMEOSTASIS15Mg1.2ITZCHAKSLOTKIANDKARLSKORECKI0.01Ca2.42Cl1006HCO32550Phos1.2A SODIUMANDWATERHOMEOSTASISEPIDEMIOLOGYDisturbancesins

2、odiumandwaterbalanceordistribution,withattendantperturbationsinthevolumeorsolutecompositionofbodyfluidcompart-ments,areamongthemostfrequentlyencounteredabnormalitiesinclinicalmedicine.Theprincipalmanifestationsofthesedisturbancesarehypovolemia,hypervolemia,dysnatremia(hyponatremiaorhypernatremia)

3、,andpolyuria.Disturbancesinbodytonicity,reflectedbyhyponatremiaorhypernatremia,areestimatedtoaffectupto15to20%ofhospitalizedpatients,withseveredisturbances(>10%deviationfromnormalvalues)affecting1to2%ofICF=2/3TBWpatients.Prevalenceratesfortheseabnormalitiesinambulatorypopulations(28L)arelower,and

4、elderlyindividualsandpatientstreatedwithmultiplemedica-tionsarethemostsusceptible.PATHOBIOLOGYISF=3/4ECFTBW=60%Approximately60%ofbodymassiscomposedofsolute-containingfluid(10.5L)weight(42L)solutionsthataredividedintoextracellularfluid(ECF)andintracellularfluidECF=1/3TBW(14L)(ICF)compartments.Wate

5、rflowsfreelyacrosscellmembranesthroughspe-cificwaterchannels(aquaporinfamilyoftransmembraneproteins)accordingtothedictatesofosmoticforces,therebymaintainingnearequalityoftheIVF=1/4ECFsolute-to-waterratio(osmolality)intheICFandECF.However,thecompo-(13.5L)sitionofthemajorsolutesdiffersbetweentheECF

6、andICF(Fig.116-1A).BSodiumandpotassiumarethemajorcationsintheECFandICF,respec-tively.ChlorideandbicarbonatearethemajoraccompanyinganionsintheFIGURE116-1.Compositionofbodyfluidcompartments. schematicrepresentationECF,andnegativechargesonorganicmoleculesmaintainelectroneutralityof(A)electrolytecomp

7、ositionofcompartmentsinhumansand(B)bodyfluidcompart-ments. inA,electrolyteconcentrationsareinmillimolesperliter;intracellularconcentra-withpotassiumintheICF.Thedifferenceincationicsolutecompositiontionsaretypicalvalues