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Passage1and2OverviewoftheDigestiveSystem-translationOverviewoftheDigestiveSystemConsiderforamomentaBigMac.ThepurposeinyoureatingaBigMac,otherthansimplehedonism,istoassimilatethenutrientsitrepresentsandmakethemavailabletobuild,repairandmaintainyourowntissues,aswellasprovideenergyforstudyingandocca-sionalotherpursuits.Youmayhaveaskedyourself-"ExactlywhatnutientsarepresentinaBigMacthatIcanassimilate?"MacDonald'scomesclosetofulldisclosureinthisregard,butwhattheydon'ttellyouisthatinordertotakeadvantageofthesenutrients,youhavetoprovidethemeanstocarefullybreakthemdownintomuchsmallermoleculesthatcanbeimportedintoblood.Luckily,yourdigestivesystemtakescareofthisverycomplexprocesssoefficientlythatmostofthetimeyoudon'tevenneedtothinkaboutit.Atitssimplest,thedigestivesystemitisatuberunningfrommouthtoanus.Thistubeislikeanassemblyline,ormoreproperly,adissemblyline.Itschiefgoalistobreakdownhugemacromolecules(proteins,fatsandstarch),whichcannotbeabsorbedintact,intosmallermolecules(aminoacids,fattyacidsandglucose)thatcanbeabsorbedacrossthewallofthetube,andintothecirculatorysystemfordisseminationaroundyourbody.ConsiderforamomentaBigMac.ThepurposeinyoureatingaBigMac,otherthansimplehedonism,istoassimlatethenutrientsitrepresentsandmakethemavailabletobuild,repairandmaintainyourowntissues,aswellasprovideenergyforstudyingandoccasio-nalotherpursuits.ThebreakdownoffoodstuffslikeaBigMacisaccomplishedthroughacombinationofmechanicalandenzymaticprocesses.Toaccomplishthisbreakdown,thedigestivetuberequiresconsiderableassistancefromaccessorydigestiveorganssuchasthesalivaryglands,liverandpancreas,whichdumptheirsecretionsintothetube.Thename"accessory"shouldnotbetakentomeandispensible;indeed,withoutpancreaticenzymesyouwouldstarvetodeathinshortorder.Inmanyways,thedigestivesystemcanbethoughtofasawell-runfactoryinwhichalargenumberofcomplextasksareperformed.Thethreefundamentalprocessesthattakeplaceare:•Secretion:Deliveryofenzymes,mucus,ionsandthelikeintothelumen,andhormonesintoblood
