Chapter8-Renal-UrinarySystemRENAL-URINARYSYSTEMSGeorgeP.HemstreetTherenalandurinarysystemsarecomprisedofacomplexseriesoforganswhichtogether聽functiontofilterwastesfromtheblood,andmanufacture,storeanddischargeurine.Theseorgansystemsarevitaltohomeostasisthroughmaintainingfluidbalance,acid-basebalanceandbloodpressure.Theprimaryorgansoftherenal-urinarysystemsarethetwokidneysandtheurinarybladder.Intheprocessoffilteringwasteproductsfromthebloodthekidneysarepotentiallyexposedtohighconcentrationsofendogenousandexogenoustoxicsubstances.Thus,somekidneycellsareexposedtoconcentrationsathousandtimeshigherthaninblood.Problemsthatresultindamagetothekidneymaybepre-renal(affectbloodsupplytothekidney),renal(affectthekidneyitself)orpost-renal(affectanypointalongthepathwhichtheurinetravelsfromthekidneytotheendoftheurethraorpenis).Post-renalproblemsareusuallyobstructiveinnature;acommonsiteofobstructionistheprostate,juxtapositionedbetweenthebladderandtheurethra.Pre-existingdiseaseoftheprostate,bladderorureters,particularlyinfection,obstructionorforeignbodiessuchasstones,cancompromisekidneyfunctionandincreasesusceptibilitytoeitheracquiredorgeneticdefects.Understandingthemicroanatomyandmolecularmechanismsofthekidneysandbladderisimportanttoassessingsusceptibilityto,andmonitoringandpreventionof,occupationalexposures.Toxicantsseemtotargetspecificpartsofthekidneyorbladderandresultintheexpressionofspecificbiomarkersdirectlyrelatedtothedamagedsegment.Historically,predispositiontodiseasehasbeenviewedfromtheepidemiologicalperspectiveofidentifyingagroupofworkersatrisk.Today,withbetterunderstandingofthefundamentalmechanismsofdisease,individualriskassessmentthroughtheuseofbiomarkersofsusceptibility,exposure,effectanddiseaseisonthehorizon.Newethicalissuesarisebecauseofthepressuretodevelopcost-effectivestrategiestoprotectworkersfromoccupationalhazards.Thepressurearises,inpart,becausegenetictestingisgainingacceptanceforevaluatingdiseasepredispositionandbiomarkersofexposureandeffectcanserveasintermediateend-pointsatwhichinterventionmaybebeneficial.Thepurposeofthischapteristoprovideamedicalreviewoftherenalandurinarysystemsonthebasisofwhichguidelinesforassessingandreducingindividualriskintheworkplacecouldbesetforthwithdueaccounttakenoftheethicalaspectsinvolved.AnatomyandPathophysiologyoftheKidneyThehumankidneyisacomplexorganwhichfunctionstofilterwastesfromthebloodthroughtheproductionofurine.Thetwokidneysalsoperformavarietyofothervitalfunctionsincludingmaintaininghomeostasis,regulatingbloodpressure,osmoticpressureandacid-basebalance.Thekidneysreceive25%ofthetotalcardiacoutputofblood,potentiallyexposingthemtoendogenousandexogenoustoxins.Thekidneysarelocatedoneachsideofthespineinthelowerportionoftheback.Eachweighsabout150gramsandisaboutthesizeofanorange.Thekidneyconsistsofthreelayers:thecortex(outerlayer),themedullaandtherenalpelvis.Bloodflowsintothecortexandmedullathroughtherenalarteryandbranchesintoincreasinglysmallerarteries.Eachofthearteriesendsinabloodfiltrationunitcalledanephron.Ahealthykidneycontainsapproximately1.2millionnephrons,strategicallypositionedwithinthecortexandmedulla.Anephronconsistsoftheglomerulus(agroupoftinybloodvessels)surroundedbyBowman'scapsule(atwo-layermembrane)thatopensintoaconvolutedtubule.Thefluidportionofblood,plasma,isforcedthroughtheglomerulusintoBowman'scapsuleandthen,asfilteredp...
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