AbsorptionofToxicantsthroughtheSkin.docx

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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