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1、MoisturizationandskinbarrierfunctionABSTRACT:Overthepastdecade，greatprogresshasbeenmadetowardelucidatingthestructureandfunctionofthestratumcorneum(SC),theoutermostlayeroftheepidermis.SCcells(corneocytes)protectagainstdesiccationandenvironmentalbytheSCislargelydependentonseveralfactors.First,i
2、ntercellularlamellarlipids,organizedpredominantlyinanorthorhombicgelphase,provideaneffectivebarriertothepassageofwaterthroughthetissue.Secondly,thediffusionpathlengthalsoretardswaterloss,sincewatermusttraversethetortuouspathcreatedbytheSClayersandcorneocyteenvelopes.Thirdly,andequallyimportan
3、t,isnaturalmoisturizingfactor(NMF),acomplexmixtureoflow-molecular-weight,water-solublecompoundsfirstformedwithintheecorneocytesbydegradationofthehistidine-richproteinknownasfilaggrin.Eachmaturationstepleadingtotheformationofaneffectivemoisturebarrier－includingcorneocytestrengthening,lipidproc
4、essing,andNMFgeneration－isinfluencedbythelevelofSChydration.Theseprocesses,aswellasthefinalstepofcorneodesmolysisthatmediatesexfoliations,areoftendisturbeduponenvironmentalchallenge,resultingindry,flakyskinconditions.ThepresentpaperreviewsourcurrentunderstandingofthebiologyoftheSC,particularl
5、yitshomeostaticmechanismsofhydration.Keywords:corneocyte,corneodesmolysis,filaggrin,naturalmoisturizingfactor,stratumcorneum.IntroductionForhumanstosurviveinaterrestrialenvironment,thelossofwaterfromtheskinmustbecarefullyregulatedbytheepidermis,afunctiondependentonthecomplexnatureofitsouterla
6、yer,thestratumcorneum(SC)(1)。TheSCisaselectivelypermeable,heterogeneous,compositeouterlayeroftheepidermisthatprotectsagainstdesiccationandenvironmentalchallenge,andretainssufficientwatertoallowittofunctioninaridenvironments.ThesmallamountofwaterlossthatdoesoccurhydratestheouterlayersoftheSC,m
7、aintainingitsflexibilityandfacilitatingtheenzymaticreactionsthatdrivetheSC’smaturation(2－4).Thewater-retainingcapacityoftheSCishighlydependentuponthephenotypeofthecorneocytes,theirspatialarrangement,theprecisecompositionandphysicalpackingofex
