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1、MoisturizationandskinbarrierfunctionABSTRACT:Overthepastdecade,greatprogresshasbeenmadetowardelucidatingthestructureandfunctionofthestratumcorneum(SC),theoutermostlayeroftheepidermis.SCcells(corneocytes)protectagainstdesiccationandenvironmentalbytheSCislargelydependentons
2、everalfactors.First,intercellularlamellarlipids,organizedpredominantlyinanorthorhombicgelphase,provideaneffectivebarriertothepassageofwaterthroughthetissue.Secondly,thediffusionpathlengthalsoretardswaterloss,sincewatermusttraversethetortuouspathcreatedbytheSClayersandcorn
3、eocyteenvelopes.Thirdly,andequallyimportant,isnaturalmoisturizingfactor(NMF),acomplexmixtureoflow-molecular-weight,water-solublecompoundsfirstformedwithintheecorneocytesbydegradationofthehistidine-richproteinknownasfilaggrin.Eachmaturationstepleadingtotheformationofaneffe
4、ctivemoisturebarrier—includingcorneocytestrengthening,lipidprocessing,andNMFgeneration—isinfluencedbythelevelofSChydration.Theseprocesses,aswellasthefinalstepofcorneodesmolysisthatmediatesexfoliations,areoftendisturbeduponenvironmentalchallenge,resultingindry,flakyskincon
5、ditions.ThepresentpaperreviewsourcurrentunderstandingofthebiologyoftheSC,particularlyitshomeostaticmechanismsofhydration.Keywords:corneocyte,corneodesmolysis,filaggrin,naturalmoisturizingfactor,stratumcorneum.IntroductionForhumanstosurviveinaterrestrialenvironment,theloss
6、ofwaterfromtheskinmustbecarefullyregulatedbytheepidermis,afunctiondependentonthecomplexnatureofitsouterlayer,thestratumcorneum(SC)(l)oTheSCisaselectivelypermeable,heterogeneous,compositeouterlayeroftheepidermisthatprotectsagainstdesiccationandenvironmentalchallenge,andret
7、ainssufficientwatertoallowittofunctioninaridenvironments.ThesmallamountofwaterlossthatdoesoccurhydratestheouterlayersoftheSC,maintainingitsflexibilityandfacilitatingtheenzymaticreactionsthatdrivetheSC'smaturation(2—4).Thewater-retainingcapacityoftheSCishighlydependentupon
8、thephenotypeofthecorneocytes,theirspatialarrangement,theprecisecompositionandphysicalpackingofex
