英语翻译.docx

英语翻译.docx

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英语翻译

第一个人

CobraProblem:

PharmacokineticsofSnakeBites

SusanStagg-Williams,DieterAndrewSchweiss,GavinSy,andH.ScottFogler

WelcometotheCobraProblem!

Mostpeoplediewithin30minutesofbeingbittenbyacobra--unlesstheyreceiveaninjectionofantivenom,thatis.Withthatcheerythoughtinmind,let'stakealookathowthehumanbodyisaffectedbycobravenom,howantivenomworks,andhowonemightusechemicalengineeringprinciplestomodeltheseinteractions.

BackgroundInformation

ThecountryofThailandishalfaworldawayfromtheUnitedStates.Itisalandofvastjungles,inquisitivepeople,andancienttraditions.Unfortunately,itisalsothehomeofsomeofthemostdangeroussnakesintheworld,andapproximately2500peopledieeachyearinThailandasadirectresultofbeingbittenbysuchsnakes.

Untilrecently,themedicalworldwasuncertainaboutthemechanismbywhichsnakevenomattackedthehumanbody.Fortunately,researchinthisareahasprogressedrapidlyinthepasttenyears,andmedicalsciencehasbeenabletodeterminewhathappenswhensomeoneisbittenbyapoisonoussnake.Thisknowledgehasresultedinthedevelopmentofantivenomsthatcansavesnakebitevictims,butonlyiftheyareinjectedintimewithanappropriatedosageofthecorrectantivenom.

Aclose-upviewofaKingCobra（Ophiophagushannah）!

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TwoofthedeadliestsnakesinThailandaretheKingCobra（Ophiophagushannah）andtheSiameseCobra（Najasiamensis）.TheKingCobra'svenomisoneofthemostlethalandfast-actingneurotoxinsfoundinnature,andtheSiameseCobra'svenomisjustastroublesome.Asinglebitefromeitherofthesesnakescanincapacitateahumanrespiratorysystemwithin30minutes,afterwhichdeathswiftlyfollows,unlessaninjectionofantivenomisimmediatelyavailable.SeetheZoocheckCanadawebsitetoreadaboutmorecobrainformation.

TheLayperson'sGuidetoHumanRespiration

Peopletendtotaketheirbreathingforgranted--it'sjustsomethingthatyoudo.IfIweretoaskyoutotakeabreath,youcouldconsciouslycontrolyourbreathing,butassoonasyourmindbegantowander,yourbodywouldtakeoverforyouagain.（Whichisgoodnewsforyou,sinceifyoustopbreathing,you'lldie!

）Butwhatreallyhappenswhenyoubreathe?

Well,ifyouthinkbacktoyourhighschoolbiologyclass,you'llrecallthatyourlungsarelikeabellowsinthewaytheydrawairintoyourbodyandexhaleitoutagain.Butyourlungsareuselesswithoutyourdiaphragmmuscle,whichdoesthepushingandpullingonyourlungstomakethemwork.Sowhenyoutakeabreath,yourbrainsendsanelectricalimpulsethroughyournervoussystemtoyourdiaphragmmuscle,tellingittodoitsthing,butwhatis"itsthing?

"

Whentheordertobreathearrivesatyourdiaphragmmuscle,thenerveendingsthatsurroundthemusclearetriggeredandtheyreleasechemicalsignalsforyourdiaphragm.Thesechemicalsignalsconsistofacetylcholinemolecules,whicharereleasedfromtransmittersitesinthenerveendings.Theacetylcholinemoleculesbindtoreceptorsitesontheindividualfibersofyourdiaphragmmuscle.（Atransmitter/receptorpairingisknownasasynapse.）

Whenenoughofthesechemicalsignalsarereceivedbyyourmusclefibers,theywillstimulateyourentirediaphragmtocontractandthenrelax.Duringrelaxation,theacetylcholinemoleculesboundtoreceptorsiteswillbreakdownandvacatethereceptorsitestheyoccupied,sothatthecontraction/relaxationcyclecanstartagain.Thishappenseverytimeyoutakeabreath.

（Ifthiswatered-downexplanationofbreathingwasn'tenoughforyou,thencheckoutamore-detailedexplanationofthemechanismofhumanrespiration.

EffectsofCobraVenom

Cobrashaveseveralmethodsfordeliveringtheirdeadlyvenomtotheirprey.Somecobrascanspittheirvenomintoavictim'seyes,causingextremepainandblindness.However,themostcommonandwellknownmethodofvenomdeliveryisinjectionintoavictim'sbodythroughtheirbite.

ACobrastriking!

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Cobrasbelongtothesub-groupofsnakesknownaselapids;thereareover270speciesofcobrasandtheirrelatives.Anelapid'svenomcontainspostsynapticneurotoxinsthatspreadrapidlyinitsvictim'sbloodstream,causingrespiratoryfailureand,eventually,death.

Cobravenomisanexampleofamoleculethatprohibitstheinteractionofacetylcholinemolecules（transmittedfromnerveendingssurroundingthediaphragmmuscle）withthereceptorsitesonthediaphragmmuscle.（SeethesectiononHumanRespirationformoredetails）.Itbindstothereceptorsites,blockingthemfrominteractingwithacetylcholinemolecules.Evenworse,thevenommoleculewillnotimmediatelybreakdownandvacatethereceptorsite,effectivelyremovingthesitefromactiveduty.

Ithasbeendeterminedthatevenifonlyathirdofthereceptorsitesonyourdiaphragmbecomeblockedbyvenom,youwillceasebreathing.Withcobravenoms,thisprocesscantakeaslittleas30minutes.Theonlywaytocounteracttheeffectsofcobravenom（ormostotherpoisonoussnakevenoms）istoinjecttheappropriateantivenomshortlyafterthebiteoccurs.Ifantivenomisunavailable,yourlifecanstillbesavedbyputtingyouonanartificialrespiratoruntiltheparalysisofthediaphragmmusclewearsoff.

（Ifthiswatered-downexplanationofeffectsofcobravenomwasn'tenoughforyou,thencheckoutamore-detailedexplanationoftheeffectsofcobravenom.）

第二个人

MechanismofAntivenom*

Antivenomactstoneutralizethepoisonousvenomofthecobraandcausesthevenomtobereleasedfromthereceptorsite.Thus,thereceptorsitesthatwerepreviouslyblockedbyvenomarenowfreetointeractwiththeacetylcholinemolecule,andnormalrespirationresumes.Thespentantivenomandtheneutralizedvenomarethenexcretedfromthebody.

Venomcomposition（anditscorrespondingtoxicity）canvaryamongcobrasfromthesamespeciesandevenfromthesamelitter--itcanalsovaryforanindividualcobraduringitslifetime--andallofthismakeseachcobrabitetrulyunique.Inordertoinsurecorrecttreatment,antibodiesspecifictoeachformofcobravenommustbedeveloped.Thecorrectantibodiesmaybesynthesizedbyinjectinghorseswithasmallamountofcobravenom,andthencollectingtheantibodiesproducedbythehorses'immunesystems.Ofcourse,largesamplesofcobravenommustbecollectedforthisprocess,andmanysnakefarmsaroundtheworldmakesignificantamountsofmoneybyharvestingthedeadlysnaketoxin.

Milkingacobraforvenom!

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Carefulexecutionoftheinjectionoftheantivenomisnecessarytoavoidanycomplicationsthatmayresultfromimpropertreatment.Iftheamountofantivenomisnotsufficienttoneutralizeallofthevenom,aportionofthereceptorsiteswillremainblockedandthepersonwouldrequiretheuseofartificialrespirationmachinesandelectricalimpulsestohavecompleterespiration.Duetothesizeoftheantivenommolecule,ifgiveningreatexcessitmayacttoshieldthereceptorsitefrominteractionwiththeacetylcholinemolecule.Thus,thevictimwoulddevelopsymptomssimilartothatofbeingbittenbyasnake.Unlikecobravenom;however,theantivenomwilleventuallybereleasedfromthebody.Therateofreleaseisveryslow,andalthoughtherearenoprovencasesofexcessantivenomcausingdeath,severeproblemssuchasparalysishaveoccurred.

*

[Thereadershouldnote,thatthecorrecttechnicaltermtousehereisantivenin,notantivenom.Theauthorsmadethedecisiontouseantivenomratherthanantivenin,becausethisisanon-technicalpresentation,andtheaveragepersonismorefamiliarwiththewordantivenom.Itisalsomoreintuitivetousethewordantivenom,whendiscussingasubstancethatworksagainstvenom.]

CobraVenomReactions

Theinteractionofthevenomandtheantivenomwiththereceptorsitescanbemodeledasareactionengineeringcatalysisproblem.Examplesofthereactionsaregivenbelow.

Adsorptionofvenomontosite:

Adsorptionofantivenomontosite:

Reactionofvenomwithantivenomonsite:

Reactionofantivenomwithvenomonsite:

Reactionofvenomandantivenominblood:

Removalofproductandreactantsfromsystem:

where:

V=venom

A=antivenom

S=unoccupiedreceptorsite

VS=siteoccupiedbyvenom

AS=siteoccupiedbyantivenom

AV=neutralizedproductfromvenom/antivenomreaction

DevelopingtheEquations

Ourdevelopmentoftheequationsyouwillneed,inordertomodelthebehaviorofvenomand/orantivenominthehumanbody,willbequickanddirty,butalsorelativelystraight-forward.Youmaywanttoreadthroughthisinformationmorethanoncetogetafeelfortheprocedure.

BatchReactorDesignEquation:

Thedesignequationforabatchreactoris:

Ifweassumethereactoriswell-mixed,thenthereactionratewillbeconstantovereverydifferentialportionofvolume,andwe'llget:

Finally,combiningthenumberofmolesofvenomintheblood,NV,withthevolumewillgiveustheconcentrationofvenomintheblood:

Thedevelopmentissimilarfortheotherrelevantconcentrationsforantivenomandvenom-antivenomproductintheblood,CAandCP,respectively.

第三个人

AnalogoustoCatalytic