【精品】生理学病案分析.doc

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1、细胞1.HyperkalemiawithMuscleWeaknessDescriptionofCase.A48-year-oldwomanwithinsulin-dependentdiabetesmellitusreportstoherphysicianthatsheexperiencingseveremuscleweakness・Sheisbeingtreatedforhypertensionwithpropranolol,aP-adrenergicblockingagent.Herphysicianimmediatelyordersbloodstudi

2、es,whichrevealaserum[K*]of6.5mEq/L(nonnaL4.5mEq/L)andelevatedBUN(bloodureanitrogen).Thephysiciantapersoffthedosageofpropranolol,witheventualdiscontinuationofthedrug・Headjustsherinsulindosage・Withinafewdays,thepatient'sserum[Kjhasdecreasedto4.7mEq/L,andshereportsthathermusclestreng

3、thhasreturnedtonomial・ExplanationofCase.Thisdiabeticpatienthasseverehyperkalemiacausedbyseveralfactors.(1)Becauseherinsulindosageisinsufficient,thelackofadequateinsulinhascausedashiftofK+outofcellsintoblood(insulinpromotesK*uptakeintocells).(2)Propranolol,thep-blockingagentusedtot

4、reatthewoman'shypertension,alsoshiftsK+outofcellsintoblood.(3)ElevatedBUNsuggeststhatthewomanisdevelopingrenalfailure;herfailingkidneysareunabletoexcretetheextraK+thatisaccumulatinginherblood.Thesemechanismsinvolveconceptsrelatedtorenalphysiologyandendocrinephysiology.Itisimportan

5、ttounderstandthatthiswomanhasaseverelyelevatedblood[IC](hyperkalemia)andthathermuscleweaknessresultsfromthishyperkalemia.Thebasisforthisweaknesscanbeexplainedasfollows.TherestingmembranepotentialofmusclecellsisdeterminedbytheconcentrationgradientforK+acrossthecellmembrane(Nemstequ

6、ation).Atrest,thecellmembraneisverypermeabletoK+,andK+diffusesoutofthecelldownitsconcentrationgradient,creatingaK+diffusionpotential・ThisK〒diffusionpotentiidisresponsiblefortherestingmembninepotential,whichiscellinteriornegative・ThelargertheK+concentrationgradient,thegreatertheneg

7、ativityinthecell・Whentheblood[K+]iselevated,theconcentrationgradientacrossthecellmembraneislessthannonnal;restingmembranepotentialwillthereforebelessnegative(ie,depolarized).Itmightbeexpectedthatthisdepolarizationwouldmakeiteasiertogenerateactionpotentialsinthemusclebecausetherest

8、ingmembranepotentialwouldbecloser