Absorption-of-Toxicants-through-the-Skin.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,andthesedifferencesaffectthepermeabilityoftheskintochemicalsthatdependsonboththediffusivityandthethicknessofthestratumcorneum.Thesecondphaseofpercutaneousabsorptionconsistsofdiffusionofthetoxicantsthroughthelowerlayersoftheepidermis(stratumgranulosum,spinosumandgermin

5、etivum)andthedermisthatcontainaporous,nonselectiveaqueousdiffusionmedium.Thenthetoxicantsenterthesystemiccirculationandlymphaticcapillaries.Andthisrateofdiffusiondependsonbloodflow,interstitialfluidmovementandperhapsinteractionswithdermalconstituents.Asisreported,someagentscouldinjurethestratumcomeu

6、mandincreaseitspcneability,whichmayenhancetheabsorptionofsometoxicants.Andthestratumcorneumthatispartiallyhydratedismorepermeablethanthatwhichisdry.Havingbeenemployedinstudyingthedermalabsorptionoftoxicants,considerablespeciesvariationshavebeenobservedincutaneouspermeability.Speciesdifferencesinperc

7、utaneousabsorptionareaccountforthedifferentialtoxicityofinsecticidesininsectsandhumans.AccordingtoDugard,theappendages(sweatducts,piIosebaceousducts)andthestratumcorneumthatarehighlyspecies-dependentareimportantindermalabsorptionofchemicals.Besides,thecutaneousbloodflowisanotherpotentialrate-limitingstepinthedermalabsorptionofchemicals.