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1、AbsorptionofToxicantsthroughtheSkin(abstract)Humanskinisnotverypermeableandthereforeisrelativelygoodbarrierforseparatingorganismsfromtheirenvironment.However,somechemicalscanbeabsorbedbyskininsufficientquantitiestoproducesystemiceffects.Tobeabsorbedthroughtheskin,atoxicantmustpassthroughtheepidermis
2、ortheappendages(sweatandsebaceousglandsandhairfollicles).Chemicalsthatareabsorbedthroughtheskinhavetopassthroughseveralcelllayers(atotalofseven)beforeenteringthesmallbloodandlymphcapillariesinthedermis.ThemostimportantconsiderationsregardingthedermalabsorptionofXenobioticsrelatetothestratumcorneum.T
3、hefirstphaseofpercutaneousabsorptionisdiffusionofXenobioticsthroughtherate-limitingbarrier,thestratumcomeumthatconsistsofabout75%to80%moderatelylipophilicmaterials.Itisclearthatalltoxicantsmoveacrossitbypassivediffusion.Moreover,humanstratumcomeumdisplayssignificantdifferencesinstructureandchemistry
4、fromoneregionofthebodytoanother,andthesedifferencesaffectthepermeabilityoftheskintochemicalsthatdependsonboththediffusivityandthethicknessofthestratumcomeum.Thesecondphaseofpercutaneousabsorptionconsistsofdiffusionofthetoxicantsthroughthelowerlayersoftheepidermis(stratumgranulosum,Spinosumandgermine
5、tivum)andthedermisthatcontainaporous,nonselectiveaqueousdiffusionmedium.Thenthetoxicantsenterthesystemiccirculationandlymphaticcapillaries.Andthisrateofdiffusiondependsonbloodflow,interstitialfluidmovementandperhapsinteractionswithdermalconstituents.Asisreported,someagentscouldinjurethestratumcomeum
6、andincreaseitspermeability,whichmayenhancetheabsorptionofsometoxicants.Andthestratumcomeumthatispartiallyhydratedismorepermeablethanthatwhichisdry.Havingbeenemployedinstudyingthedermalabsorptionoftoxicants,considerablespeciesvariationshavebeenobservedincutaneouspermeability.Speciesdifferencesinpercu
7、taneousabsorptionareaccountforthedifferentialtoxicityofinsecticidesininsectsandhumans.AccordingtoDugard,theappendages(sweatducts,piIosebaceousducts)andthestratumcorneumthatarehighlyspecies-dependentareimportantindermalabsorptionofchemicals.Besides,thecutaneousbldflowisanotherpotentialrate-limitingstepinthedermalabsorptionofchemicals.环科系02级陈熙B02174127
