Chapter4-DigestiveSystemDIGESTIVESYSTEMG.Frada**Adaptedfrom3rdedition,EncyclopaediaofOccupationalHealthandSafety.Thedigestivesystemexertsaconsiderableinfluenceontheefficiencyandworkcapacityofthebody,andacuteandchronicillnessesofthedigestivesystemareamongthecommonestcausesofabsenteeismanddisablement.Inthiscontext,theoccupationalphysicianmaybecalleduponineitherofthefollowingwaystooffersuggestionsconcerninghygieneandnutritionalrequirementsinrelationtotheparticularneedsofagivenoccupation:toassesstheinfluencethatfactorsinherentintheoccupationmayhaveeitherinproducingmorbidconditionsofthedigestivesystem,orinaggravatingothersthatmaypre-existorbeotherwiseindependentoftheoccupation;ortoexpressanopinionconcerninggeneralorspecificfitnessfortheoccupation.Manyofthefactorsthatareharmfultothedigestivesystemmaybeofoccupationalorigin;frequentlyanumberoffactorsactinconcertandtheiractionmaybefacilitatedbyindividualpredisposition.Thefollowingareamongthemostimportantoccupationalfactors:industrialpoisons;physicalagents;andoccupationalstresssuchastension,fatigue,abnormalpostures,frequentchangesinworktempo,shiftwork,nightworkandunsuitableeatinghabits(quantity,qualityandtimingofmeals).ChemicalHazardsThedigestivesystemmayactasaportalfortheentryoftoxicsubstancesintothebody,althoughitsrolehereisnormallymuchlessimportantthanthatoftherespiratorysystemwhichhasanabsorptionsurfaceareaof80-100m2whereasthecorrespondingfigureforthedigestivesystemdoesnotexceed20m2.Inaddition,vapoursandgasesenteringthebodybyinhalationreachthebloodstreamandhencethebrainwithoutmeetinganyintermediatedefence;however,apoisonthatisingestedisfilteredand,tosomedegree,metabolizedbytheliverbeforereachingthevascularbed.Nevertheless,theorganicandfunctionaldamagemayoccurbothduringentryintoandeliminationfromthebodyorasaresultofaccumulationincertainorgans.Thisdamagesufferedbythebodymaybetheresultoftheactionofthetoxicsubstanceitself,itsmetabolitesorthefactthatthebodyisdepletedofcertainessentialsubstances.Idiosyncrasyandallergicmechanismsmayalsoplayapart.Theingestionofcausticsubstancesisstillafairlycommonaccidentaloccurrence.InaretrospectivestudyinDenmark,theannualincidencewasof1/100,000withanincidenceofhospitalizationof0.8/100,000adultperson-yearsforoesophagealburns.Manyhouseholdchemicalsarecaustic.Toxicmechanismsarehighlycomplexandmayvaryconsiderablyfromsubstancetosubstance.Someelementsandcompoundsusedinindustrycauselocaldamageinthedigestivesystemaffecting,forexample,themouthandneighbouringarea,stomach,intestine,liverorpancreas.Solventshaveparticularaffinityforlipid-richtissues.Thetoxicactionisgenerallycomplexanddifferentmechanismsareinvolved.Inthecaseofcarbontetrachloride,liverdamageisthoughttobemainlyduetotoxicmetabolites.Inthecaseofcarbondisulphide,gastrointestinalinvolvementisattributedtothespecificneurotropicactionofthissubstanceontheintramuralplexuswhilstliverdamageseemstobemoreduetothesolvent'scytotoxicaction,whichproduceschangesinlipoproteinmetabolism.Liverdamageconstitutesanimportantpartofthepathologyofexogenicpoisonssincetheliveristheprimeorganinmetabolizingtoxicagentsandactswiththekidneysindetoxicationprocesses.Thebilereceivesfromtheliver,eitherdirectlyorafterconjugation,varioussubstancesthatcanbereabsorbedintheenterohepaticcycle(forinstance,cadmium,cobalt,manganese).Livercellsparticipateinoxidation(e.g.,alcohols,phenols,toluene...
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