Chapter 1 - Blood.docxVIP专享VIP免费原创优质

Chapter1-BloodHAEMATOPOIETICANDLYMPHATICSYSTEMBernardD.GoldsteinThelymphohaemopoieticsystemconsistsoftheblood,thebonemarrow,thespleen,thethymus,lymphaticchannelsandlymphnodes.Thebloodandbonemarrowtogetherarereferredtoasthehaematopoieticsystem.Thebonemarrowisthesiteofcellproduction,continuallyreplacingthecellularelementsoftheblood(erythrocytes,neutrophilsandplatelets).Productionisundertightcontrolofagroupofgrowthfactors.Neutrophilsandplateletsareusedastheyperformtheirphysiologicalfunctions,anderythrocyteseventuallybecomesenescentandoutlivetheirusefulness.Forsuccessfulfunction,thecellularelementsofthebloodmustcirculateinpropernumbersandretainboththeirstructuralandphysiologicalintegrity.Erythrocytescontainhaemoglobin,whichpermitsuptakeanddeliveryofoxygentotissuestosustaincellularmetabolism.Erythrocytesnormallysurviveinthecirculationfor120dayswhilesustainingthisfunction.Neutrophilsarefoundinbloodontheirwaytotissuestoparticipateintheinflammatoryresponsetomicrobesorotheragents.Circulatingplateletsplayakeyroleinhaemostasis.Theproductionrequirementofthebonemarrowisaprodigiousone.Daily,themarrowreplaces3billionerythrocytesperkilogramofbodyweight.Neutrophilshaveacirculatinghalf-lifeofonly6hours,and1.6billionneutrophilsperkilogramofbodyweightmustbeproducedeachday.Theentireplateletpopulationmustbereplacedevery9.9days.Becauseoftheneedtoproducelargenumbersoffunctionalcells,themarrowisremarkablysensitivetoanyinfectious,chemical,metabolicorenvironmentalinsultthatimpairsDNAsynthesisordisruptstheformationofthevitalsubcellularmachineryoftheredbloodcells,whitebloodcellsorplatelets.Further,sincethebloodcellsaremarrowprogeny,theperipheralbloodservesasasensitiveandaccuratemirrorofbonemarrowactivity.Bloodisreadilyavailableforassayviavenipuncture,andexaminationofthebloodcanprovideanearlyclueofenvironmentallyinducedillness.Thehaematologicalsystemcanbeviewedasbothservingasaconduitforsubstancesenteringthebodyandasanorgansystemthatmaybeadverselyaffectedbyoccupationalexposurestopotentiallyharmfulagents.Bloodsamplesmayserveasabiologicalmonitorofexposureandprovideawaytoassesstheeffectsofoccupationalexposureonthelymphohaematopoieticsystemandotherbodyorgans.Environmentalagentscaninterferewiththehaematopoieticsysteminseveralways,includinginhibitionofhaemoglobinsynthesis,inhibitionofcellproductionorfunction,leukaemogenesisandincreasedredbloodcelldestruction.Abnormalityofbloodcellnumberorfunctioncauseddirectlybyoccupationalhazardscanbedividedintothoseforwhichthehaematologicalproblemisthemostimportanthealtheffect,suchasbenzene-inducedaplasticanaemia,andthoseforwhichtheeffectsonthebloodaredirectbutoflesssignificancethantheeffectsonotherorgansystems,suchaslead-inducedanaemia.Sometimeshaematologicaldisordersareasecondaryeffectofaworkplacehazard.Forexample,secondarypolycythaemiacanbetheresultofanoccupationallungdisease.Table1.1liststhosehazardswhicharereasonablywellacceptedashavingadirecteffectonthehaematologicalsystem.Table1.1SelectedagentsimplicatedinenvironmentallyandoccupationallyacquiredmethaemoglobinaemiaNitrate-contaminatedwellwaterNitrousgases(inweldingandsilos)AnilinedyesFoodhighinnitratesornitritesMothballs(containingnaphthalene)PotassiumchlorateNitrobenzenesPhenylenediamineToluenediamineExamplesofWorkplaceHazardsPrimarilyAffectingtheHaematologicalSystemBenzeneBenzenewasidentifiedasa...