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1、VirtualexperimentExperiment13Regulationofurineformation[Objectives]1.Toinvestigatetheeffectsofincreasedplasmavolume,hyperglycemia,norepinephrine,furosemide,pituitrinandvagusnerveactivationonvolumeofurine,andtounderstandtheunderlyingmechanisms.2.Toexaminethesecretionfunctionofrenaltubulesbythe
2、phenolredtimetest.[Principles]Theformationofurineincludesthreerenalprocesses:(1)glomerularfiltration,(2)tubularreabsorptionoffiltrateand(3)tubularsecretion.Anyfactorsthataffectthesethreeprocessesofurineformationwillinfluencetheurinevolumeandcomponentsintheurine(Figure1).Becauseofthehighpermea
3、bilityoftheglomerularmembrane,allthecomponentsintheplasmaexceptplasmaproteinarefilteredintoBowman’scapsule.Thevolumeoffiltrateisdeterminednotonlybyhydrostaticpressureandcolloidosmoticforcesacrosstheglomerularmembrane,butalsobythepermeabilityandsurfaceareaoffiltrationmembrane.Norepinephrine(NE
4、),whichisaneurotransmitterreleasedfromsympatheticnerveendings,constrictsrenalarteriestodecreaseglomerularhydrostaticpressure,anddecreasethevolumeofurine.Activationofthevagusnervedepressesarterialbloodpressure(includingrenalarterialpressure)todecreaseglomerularhydrostaticpressure,anddecreaseth
5、evolumeofurine.Whenfiltrateflowsthroughtherenaltubule,somesubstancessuchasglucosearealmostcompletelyreabsorbed,andotherssuchassodiumionsarepartlyreabsorbed.Withsolutereabsorption,morethan99%offilteredwaterisabsorbedtoo.Butinpatientswithdiabetesmellitus,whenthereismorethan180mg/dlglucoseinbloo
6、daswellasinfiltrate,alltheglucoseinthefiltratecannotbereabsorbedduetosaturationoftheglucosetransportcapacityoftheproximaltubule(concentrationofbloodglucoseexceedsthethresholdlevelforreabsorptionbythekidneys).Sosomeglucosestaysintheurine,increasingitsosmolarity,andcausingincreasedurinevolume.+
7、+-Furosemide,aninhibitoroftheNa-K-2Clco-transporterlocatedinthethicksegmentoftheascendinglimb,cangreatlydecreasethereabsorptionoftheseions,tocauselargequantitiesofwatertobeexcreted(polyuria)(Figure1).Atrialnatriureticpeptide(ANP)issynthesized
