醫(yī)學(xué)英語原文翻譯1至5單元

1、醫(yī)學(xué)英語原文翻譯1至5單元1.生理學(xué)是研究生物體正常功能的一門科學(xué)。它研究生物體如何進(jìn)行各種活動，如何飲食，如何運(yùn)動，如何適應(yīng)不斷改變的環(huán)境，如何繁殖后代。這門學(xué)科包羅萬象，涵蓋了生物體整個生命過程。生理學(xué)成功地解釋了生物體如何進(jìn)行日?；顒?，基于的觀點(diǎn)是生物體好比是結(jié)構(gòu)復(fù)雜而靈巧的機(jī)器，其操作受物理和化學(xué)規(guī)律控制。盡管從生物學(xué)整個范疇看，生物體某些活動過程是相似的，如基因編碼的復(fù)制，但許多過程還是某些生物體群組特有的。鑒于此，將這門學(xué)科分成不同部分研究如細(xì)菌生理學(xué)，植物生理學(xué)和動物生理學(xué)是有必要的。Physiologyisthestudyofthefunctionsoflivingmatter

2、.Itisconcernedwithhowanorganismperformsitsvariedactivities:howitfeeds,howitmoves,howitadaptstochangingcircumstances,howitspawnsnewgenerations.Thesubjectisvastandembracesthewholeoflife.Thesuccessofphysiologyinexplaininghoworganismsperformtheirdailytasksisbasedonthenotionthattheyareintricateandexquisi

3、temachineswhoseoperationisgovernedbythelawsofphysicsandchemistry.Althoughsomeprocessesaresimilaracrossthewholespectrumofbiologythereplicationofthegeneticcodeforexamplemanyarespecifictoparticulargroupsoforganisms.Forthisreasonitisnecessarytodividethesubjectintovariouspartssuchasbacterialphysiology,pl

4、antphysiology,andanimalphysiology.2.正如要了解一個動物如何活動，首先需要了解它的構(gòu)成，要充分了解一個生物體的生理學(xué)活動就必須掌握全面的解剖學(xué)知識。一個生物體的各部分起著什么作用可通過實(shí)驗(yàn)觀察得知。盡管我們對志愿者進(jìn)行了許多重要的生理調(diào)查，但是實(shí)驗(yàn)條件需要精確控制，所以我們當(dāng)前大多生理知識還是源于對其它動物如青蛙，兔子，貓和狗等的研究。當(dāng)我們明確大多數(shù)動物物種的特定生理過程存在共同之處時，相同的生理原理適用于人類也是合理的。通過這種方法，我們獲得了大量的知識，從而讓我們對人類生理學(xué)有了更深入的了解，為我們有效治療許多疾病提供了一個堅(jiān)實(shí)的基礎(chǔ)。Tostudyho

5、wananimalworksitisfirstnecessarytoknowhowitisbuilt.Afullappreciationofthephysiologyofanorganismmustthereforebebasedonasoundknowledgeofitsanatomy.Experimentscanthenbecarriedouttoestablishhowparticularpartsperformtheirfunctions.Althoughtherehavebeenmanyimportantphysiologicalinvestigationsonhumanvolunt

6、eers,theneedforprecisecontrolovertheexperimentalconditionshasmeantthatmuchofourpresentphysiologicalknowledgehasbeenderivedfromstudiesonotheranimalssuchasfrogs,rabbits,cats,anddogs.Whenitisclearthataspecificphysiologicalprocesshasacommonbasisinawidevarietyofanimalspecies,itisreasonabletoassumethatthe

7、sameprincipleswillapplytohumans.Theknowledgegainedfromthisapproachhasgivenusagreatinsightintohumanphysiologyandendoweduswithasolidfoundationfortheeffectivetreatmentofmanydiseases.Theorganizationofthebody3.機(jī)體的基本組成物質(zhì)是細(xì)胞，細(xì)胞結(jié)合在一起形成組織。組織的基本類型有上皮組織，結(jié)締組織，神經(jīng)組織，肌組織，每類組織都有各自的特征。許多結(jié)締組織中細(xì)胞量相對較少，但是有大量的細(xì)胞外基質(zhì)。相比而言

8、，光滑的肌組織由大量密密麻麻的肌細(xì)胞通過特定的細(xì)胞連接組成。各種器官如腦，心臟，肺，小腸和肝等由不同種類的組織聚集而成。這些器官是不同生理系統(tǒng)的組成部分。心臟和血管組成心血管系統(tǒng)；肺，器官，支氣管，胸壁和膈肌組成呼吸系統(tǒng)；骨骼和骨骼肌組成骨骼肌系統(tǒng)；大腦，脊髓，自主神經(jīng)和神經(jīng)中樞以及周圍軀體神經(jīng)組成神經(jīng)系統(tǒng)等等。3.Thebuildingblocksofthebodyarethecells,whicharegroupedtogethertoformtissues.Theprincipaltypesoftissueareepithelial,connective,nervous,andmuscu

9、lar,eachwithitsowncharacteristics.Manyconnectivetissueshaverelativelyfewcellsbuthaveanextensiveextracellularmatrix.Incontrast,smoothmuscleconsistsofdenselypackedlayersofmusclecellslinkedtogetherviaspecificcelljunctions.Organssuchasthebrain,theheart,thelungs,theintestines,andtheliverareformedbytheagg

10、regationofdifferentkindsoftissues.Theorgansarethemselvespartsofdistinctphysiologicalsystems.Theheartandbloodvesselsformthecardiovascularsystem;thelungs,trachea,andbronchitogetherwiththechestwallanddiaphragmformtherespiratorysystem;theskeletonandskeletalmusclesformthemusculoskeletalsystem;thebrain,sp

11、inalcord,autonomicnervesandganglia,andperipheralsomaticnervesformthenervoussystem,andsoon.4.細(xì)胞在形體和功能上差異很大，但是它們有某些共同的特征。第一，細(xì)胞由一層薄膜也稱細(xì)胞膜包被；第二，細(xì)胞能把大分子分解為小分子釋放能量供活動所需；第三，在生命過程中某個階段，細(xì)胞體內(nèi)存在一個以脫氧核糖核酸(DNA)形式出現(xiàn)，包含基因信息的細(xì)胞核。4.Cellsdifferwidelyinformandfunctionbuttheyallhavecertaincommoncharacteristics.First,th

12、eyareboundedbyalimitingmembrane,theplasmamembrane.Secondly,theyhavetheabilitytobreakdownlargemoleculestosmalleronestoliberateenergyfortheiractivities.Thirdly,atsomepointintheirlifehistory,theypossessanucleuswhichcontainsgeneticinformationintheformofdeoxyribonucleicacid（DNA）.5.活體細(xì)胞不斷轉(zhuǎn)化物質(zhì)。細(xì)胞分解葡萄糖和脂肪，為

13、自身生長和修復(fù)所需的蛋白質(zhì)合成和運(yùn)動等其它活動提供能量。這些化學(xué)變化統(tǒng)稱為新陳代謝。把大分子分解為小分子的過程稱為分解代謝，小分子合成大分子的過程稱為合成代謝。5. Livingcellscontinuallytransformmaterials.Theybreakdownglucoseandfatstoprovideenergyforotheractivitiessuchasmotilityandthesynthesisofproteinsforgrowthandrepair.Thesechemicalchangesarecollectivelycalledmetabolism.Thebre

14、akdownoflargemoleculestosmalleronesiscalledcatabolismandthesynthesisoflargemoleculesfromsmalleronesanabolism.6.細(xì)胞在進(jìn)化過程中不斷分化進(jìn)行不同的功能活動。有些細(xì)胞具有收縮能力（如肌細(xì)胞），有些可以傳導(dǎo)電信號（如神經(jīng)細(xì)胞）。進(jìn)一步進(jìn)化的細(xì)胞能夠分泌不同物質(zhì)如荷爾蒙(如內(nèi)分泌細(xì)胞)或酶。胚胎發(fā)育過程中，分化的過程由于很多不同細(xì)胞來源于受精卵而再次發(fā)生。6. Inthecourseofevolution,cellsbegantodifferentiatetoservedifferentfu

15、nctions.Somedevelopedtheabilitytocontract(musclecells),otherstoconductelectricalsignals(nervecells).Afurthergroupdevelopedtheabilitytosecretedifferentsubstancessuchashormonesorenzymes.Duringembryologicaldevelopment,thisprocessofdifferentiationisre-enactedasmanydifferenttypesofcellareformedfromthefer

16、tilizedegg.7.大多數(shù)組織包含有不同的細(xì)胞類型。比如，血液中含紅細(xì)胞，白細(xì)胞和血小板。紅細(xì)胞運(yùn)輸全身的氧氣。白細(xì)胞在抵御感染時起重要作用，血小板是血液凝集過程中重要的成分。結(jié)締組織有多種不同類型，但有一個共同特征，即細(xì)胞分布在豐富的細(xì)胞外基質(zhì)中。神經(jīng)組織含神經(jīng)細(xì)胞和神經(jīng)膠質(zhì)細(xì)胞。7.Mosttissuescontainamixtureofcelltypes.Forexample,bloodconsistsofredcells,whitecells,andplatelets.Redcellstransportoxygenaroundthebody.Thewhitecellsplayan

17、importantroleindefenseagainstinfectionandtheplateletsarevitalcomponentsintheprocessofbloodclotting.Thereareanumberofdifferenttypesofconnectivetissuebutallarecharacterizedbyhavingcellsdistributedwithinanextensivenoncellularmatrix.Nervetissuecontainsnervecellsandglialcells.8.大型多細(xì)胞動物體的細(xì)胞不能產(chǎn)生氧氣和營養(yǎng)物質(zhì)，需要直

18、接從外界環(huán)境中獲取。這些氧氣和營養(yǎng)物質(zhì)必須由血液運(yùn)送到細(xì)胞。這是血液的主要功能之一，血液憑借心臟的泵血作用在血管內(nèi)流動循環(huán)。8. Thecellsoflargemulticellularanimalscannotderivetheoxygenandnutrientstheyneeddirectlyfromtheexternalenvironment.Thesemustbetransportedtothecells.Thisisoneoftheprincipalfunctionsoftheblood,whichcirculateswithinbloodvesselsbyvirtueofthepu

19、mpingactionoftheheart.Theheart,bloodvessels,andassociatedtissuesformthecardiovascularsystem.9. 心臟有四個腔，其中有兩個心房，兩個心室構(gòu)成了一對并排存在的泵。右心室將去氧的血液泵至肺中，肺中的血液吸收空氣中的氧氣，而左心室把從肺回流來的有氧血液泵出至身體其它部位，供應(yīng)給各組織。生理學(xué)家研究促使心臟跳動的因素，心臟如何泵送血液使其循環(huán)，心臟如何根據(jù)各組織所需分配血液。血漿和組織間的流動液體交換流入淋巴系統(tǒng)，最終回流到血液中。10. Theheartconsistsoffourchambers,twoat

20、riaandtwoventricles,whichformapairofpumpsarrangedsidebyside.Therightventriclepumpsdeoxygenatedbloodtothelungswhereitabsorbsoxygenfromtheair,whiletheleftventriclepumpsoxygenatedbloodreturningfromthelungstotherestofbodytosupplythetissues.Physiologistsareconcernedwithestablishingthefactorsresponsiblefo

21、rtheheartbeat,howtheheartpumpsthebloodaroundthecirculation,andhowitisdistributedtoperfusethetissuesaccordingtotheirneeds.Fluidexchangedbetweenthebloodplasmaandthetissuespassesintothelymphaticsystem,whicheventuallydrainsbackintotheblood.11. 機(jī)體進(jìn)行各項(xiàng)活動所需的能量最終來源于呼吸。這一過程包括食物（主要是糖類和脂肪）的氧化，釋放它們所含的能量。這一過程中，氧

22、氣來自于肺中的空氣，經(jīng)由血液到達(dá)全身各組織。組織呼吸活動中釋放的二氧化碳由肺動脈中的血液運(yùn)送至肺，然后呼氣排出體外。需回答的基本問題如下：空氣是如何進(jìn)出肺的？呼吸的空氣量如何適應(yīng)機(jī)體所需？限制肺吸收氧氣頻率的因素是什么？10. Theenergyrequiredforperformingthevariousactivitiesofthebodyisultimatelyderivedfromrespiration.Thisprocessinvolvestheoxidationoffoodstuffstoreleasetheenergytheycontain.Theoxygenneededfort

23、hisprocessisabsorbedfromtheairinthelungsandcarriedtothetissuesbytheblood.Thecarbondioxideproducedbytherespiratoryactivityofthetissuesiscarriedtothelungsbythebloodinthepulmonaryarterywhereitisexcretedintheexpiredair.Thebasicquestionstobeansweredincludethefollowing:Howistheairmovedinandoutofthelungs?H

24、owisthevolumeofairbreathedadjustedtomeettherequirementsofthebody?Whatlimitstherateofoxygenuptakeinthelungs?11. 機(jī)體所需營養(yǎng)物質(zhì)來源于飲食。食物經(jīng)口腔進(jìn)入體內(nèi)，在胃腸道內(nèi)經(jīng)酶將其分解成小分子物質(zhì)。這些消化物通過腸壁吸收入血液，通過門靜脈進(jìn)入肝臟。經(jīng)肝臟作用后，這些營養(yǎng)物質(zhì)能夠滿足組織生長修復(fù)及能量需求。在消化系統(tǒng)部分，重要的生理學(xué)問題是：食物是如何消化的？食物如何被個體分解消化？個體營養(yǎng)物質(zhì)如何吸收？食物如何在腸內(nèi)轉(zhuǎn)運(yùn)的？未消化的殘留如何從體內(nèi)排出？11.Thenutrientsnee

25、dedbythebodyarederivedfromthediet.Foodistakeninbythemouthandbrokendownintoitscomponentpartsbyenzymesinthegastrointestinaltract.Thedigestiveproductsarethenabsorbedintothebloodacrossthewalloftheintestineandpasstotheliverviatheportalvein.Thelivermakesnutrientsavailabletothetissuesbothfortheirgrowthandr

26、epairandfortheproductionofenergy.Inthecaseofthedigestivesystem,keyphysiologicalquestionsare:Howisfoodingested?Howisitbrokendownanddigested?Howaretheindividualnutrientsabsorbed?Howisthefoodmovedthroughthegut?Howaretheindigestibleremainseliminatedfromthebody?12. 腎臟主要功能是控制細(xì)胞外液體的形成。在這一過程中，腎臟也會把不可揮發(fā)的廢物排出

27、去。為行使這一功能，在排出之前，腎臟產(chǎn)生含有各種成分的尿液并將其暫時儲存在膀胱中。這一部分主要的生理學(xué)問題是：腎臟如何調(diào)節(jié)血液中的成分？如何排出有毒廢物？如何應(yīng)對像脫水這樣的應(yīng)激反應(yīng)？以及尿液可以存儲和排出體外的機(jī)制是什么？12.Thechieffunctionofthekidneysistocontrolthecompositionoftheextracellularfluid.Inthecourseofthisprocess,theyalsoeliminatenon-volatilewasteproductsfromtheblood.Toperformthesefunctions,thek

28、idneysproduceurineofvariablecompositionwhichistemporarilystoredinthebladderbeforevoiding.Thekeyphysiologicalquestionsinthiscaseare:howdothekidneysregulatethecompositionoftheblood?Howdotheyeliminatetoxicwaste?Howdotheyrespondtostressessuchasdehydration?Whatmechanismsallowthestorageandeliminationofthe

29、urine?Thereproductivesystem13.生殖是活生物體的一個基本特征。生殖腺產(chǎn)生專門的性細(xì)胞，被稱為配子。性生殖的核心是雌雄配子即精子和卵子的產(chǎn)生和融合，因此兩個獨(dú)立個體的基因特征融合而產(chǎn)生一個基因上與雙親不同的后代。13.Reproductionisoneofthefundamentalcharacteristicsoflivingorganisms.Thegonadsproducespecializedsexcellsknownasgametes.Atthecoreofsexualreproductionisthecreationandfusionofthemalean

30、dfemalegametes,thespermandova(eggs),withtheresultthatthegeneticcharacteristicsoftwoseparateindividualsaremixedtoproduceoffspringthatdiffergeneticallyfromtheirparents14.這一系統(tǒng)由骨、骨骼肌、關(guān)節(jié)和它們的相關(guān)組織組成。其主要功能是提供運(yùn)動需要，維持姿勢及呼吸運(yùn)動。它也為內(nèi)臟器官提供物理支持。這一部分，肌肉收縮機(jī)制是主要問題。內(nèi)分泌系統(tǒng)和神經(jīng)系統(tǒng)14 .Thisconsistsofthebonesoftheskeleton,skel

31、etalmuscles,joints,andtheirassociatedtissues.Itsprimaryfunctionistoprovideameansofmovement,whichisrequiredforlocomotion,forthemaintenanceofposture,andforbreathing.Italsoprovidesphysicalsupportfortheinternalorgans.Herethemechanismofmusclecontractionisacentralissue.Theendocrineandnervoussystems15 .不同器

32、官系統(tǒng)的活動需要協(xié)作和調(diào)節(jié)，以便共同作用滿足機(jī)體需要。人體有兩大調(diào)節(jié)系統(tǒng)：神經(jīng)系統(tǒng)和內(nèi)分泌系統(tǒng)。神經(jīng)系統(tǒng)通過電信號迅速將信息傳導(dǎo)給特定細(xì)胞。這樣神經(jīng)將電信號傳遞給骨骼肌以控制收縮。內(nèi)分泌系統(tǒng)分泌化學(xué)物質(zhì)激素。激素通過血流到達(dá)施與調(diào)節(jié)作用的細(xì)胞。激素在許多不同器官中起著重要作用，在月經(jīng)期調(diào)節(jié)和其它生殖方面尤其重要。15. Theactivitiesofthedifferentorgansystemsneedtobecoordinatedandregulatedsothattheyacttogethertomeettheneedsofthebody.Twocoordinatingsystemsha

33、veevolved:thenervoussystemandtheendocrinesystem.Thenervoussystemuseselectricalsignalstotransmitinformationveryrapidlytospecificcells.Thusthenervespasselectricalsignalstotheskeletalmusclestocontroltheircontraction.Theendocrinesystemsecreteschemicalagents,hormones,whichtravelinthebloodstreamtothecells

34、uponwhichtheyexertaregulatoryeffect.Hormonesplayamajorroleintheregulationofmanydifferentorgansandareparticularlyimportantintheregulationofthemenstrualcycleandotheraspectsofreproduction.16. 免疫系統(tǒng)通過殺死入侵的有機(jī)體，清除致病或損傷細(xì)胞為機(jī)體提供防御功能。17. Theimmunesystemprovidesthebodysdefensesagainstinfectionbothbykillinginvad

35、ingorganismsandbyeliminatingdiseasedordamagedcells.18. 雖然研究各器官如何行使功能很有益處，但我們必須認(rèn)識到機(jī)體作為一個整體所做的活動依賴于各器官系統(tǒng)間錯綜復(fù)雜的相互作用。如果一部分無法正常工作，全身其它器官系統(tǒng)也會受到影響。例如，如果腎臟出現(xiàn)問題，內(nèi)部環(huán)境的調(diào)節(jié)受損，結(jié)果導(dǎo)致其它器官系統(tǒng)功能紊亂。17. Althoughitishelpfultostudyhoweachorganperformsitsfunctions,itisessentialtorecognizethattheactivityofthebodyasawholeisde

36、pendentontheintricateinteractionsbetweenthevariousorgansystems.Ifonepartfails,theconsequencesarefoundinotherorgansystemsthroughoutthewholebody.Forexample,ifthekidneysbegintofail,theregulationoftheinternalenvironmentisimpairedwhichinturnleadstodisordersoffunctionelsewhere.18. 各種復(fù)雜機(jī)制共同作用調(diào)節(jié)細(xì)胞外液的形成，不同個體

37、細(xì)胞有自身機(jī)制調(diào)節(jié)內(nèi)在組成成分。盡管外界環(huán)境和動物活動不停變化，調(diào)節(jié)機(jī)制維持著體內(nèi)環(huán)境的穩(wěn)定。內(nèi)部環(huán)境的穩(wěn)定被稱為穩(wěn)態(tài)，它是機(jī)體能夠正常發(fā)揮作用所必須的。18.Complexmechanismsareatworktoregulatethecompositionoftheextracellularfluidandindividualcellshavetheirownmechanismsforregulatingtheirinternalcomposition.Theregulatorymechanismsstabilizetheinternalenvironmentdespitevariatio

38、nsinboththeexternalworldandtheactivityoftheanimal.Theprocessofstabilizationoftheinternalenvironmentiscalledhomeostasisandisessentialifthecellsofthebodyaretofunctionnormally.19. 例如，心臟的跳動依賴于心肌細(xì)胞有節(jié)律的收縮。這一活動依賴于電信號，而電信號反過來依賴存在于細(xì)胞外和細(xì)胞內(nèi)液體中鈉和鉀離子的濃度。如果細(xì)胞外液中鉀離子過多，心肌細(xì)胞興奮性增強(qiáng)，可能出現(xiàn)不規(guī)律的收縮。因此，要維持心臟正常跳動，細(xì)胞外液中鉀離子的濃度就

39、必須控制在一定范圍內(nèi)。20. Totakeoneexample,thebeatingoftheheartdependsontherhythmicalcontractionsofcardiacmusclecells.Thisactivitydependsonelectricalsignalswhich,inturn,dependontheconcentrationofsodiumandpotassiumionsintheextracellularandintracellularfluids.Ifthereisanexcessofpotassiumintheextracellularfluid,t

40、hecardiacmusclecellsbecometooexcitableandmaycontractatinappropriatetimesratherthaninacoordinatedmanner.Consequently,theconcentrationofpotassiumintheextracellularfluidmustbekeptwithinanarrowrangeiftheheartistobeatnormally.21. 一天中，一個成人需要消耗約1千克食物，2-3升液體。以一個月計(jì)算，這相當(dāng)于約30千克食物，60-90升液體。然而，一般來說，機(jī)體體重是基本不變的。這類

41、個體可以說處于平衡狀態(tài)。食物和液體的攝入量相當(dāng)于正常機(jī)體活動消耗的能量加上尿液和糞便中丟失的能量。在一些情況下，如饑餓狀態(tài)，攝入量與機(jī)體所需量并不相當(dāng)，肌組織斷裂，提供葡萄糖產(chǎn)生能量。蛋白質(zhì)的攝入低于肌組織斷裂的速度，機(jī)體處于負(fù)氮平衡。同樣地，如果機(jī)體組織正處于生長期，如生長期的兒童，孕婦和早期訓(xùn)練階段的運(yùn)動員，那么蛋白質(zhì)的日常攝入量比正常機(jī)體所需要的多。相反，此時個體處于正氮平衡。20. Inthecourseofaday,anadultconsumesapproximately1kgoffoodanddrinks23litersoffluid.Inamonth,thisisequivale

42、nttoaround30kgoffoodand60-90litersoffluid.Yet,ingeneral,bodyweightremainsremarkablyconstant.Suchindividualsaresaidtobeinbalance;theintakeoffoodanddrinkmatchestheamountsusedtogenerateenergyfornormalbodilyactivitiesplusthelossesinurineandfeces.Insomecircumstances,suchasstarvation,intakedoesnotmatchthe

43、needsofthebodyandmuscletissueisbrokendowntoprovideglucoseforthegenerationofenergy.Here,theintakeofproteinislessthantherateofbreakdownandtheindividualissaidtohaveanegativenitrogenbalance.Equally,ifthebodytissuesarebeingbuiltup,asisthecaseforgrowingchildren,pregnantwomenandathletesintheearlystagesoftr

44、aining,thedailyintakeofproteinisgreaterthanthenormalbodyturnoverandtheindividualisinpositivenitrogenbalance.21. 平衡的概念可以應(yīng)用到機(jī)體的任何構(gòu)成成分上，包括水和鹽，而且平衡在機(jī)體調(diào)節(jié)其自身成分上是非常重要的。攝入必須等于所需，為維持機(jī)體平衡，任何多余的能量都必須排出。此外，因?yàn)闄C(jī)體的每種化學(xué)成分都有一個可取的濃度范圍，控制機(jī)制維持這個范圍。例如，兩餐間血糖濃度大約為4-5mmol.l-1.進(jìn)食后不久，血糖含量超過這一范圍，刺激胰腺分泌胰島素，降低濃度。隨著葡萄糖濃度的下降，胰島素分

45、泌減少。在此情況下，循環(huán)胰島素水平的改變都是為了使血漿中的葡萄糖維持在一個合適的范圍內(nèi)。這種調(diào)節(jié)稱為負(fù)反饋機(jī)制。在胰島素分泌期間，葡萄糖像肝糖原或脂肪一樣被儲存。21. Thisconceptofbalancecanbeappliedtoanyofthebodyconstituentsincludingwaterandsaltandisimportantinconsideringhowthebodyregulatesitsowncomposition.Intakemustmatchrequirementsandanyexcessmustbeexcretedforbalancetobemaint

46、ained.Additionally,foreachchemicalconstituentofthebodythereisadesirableconcentrationrange,whichthecontrolmechanismsareadaptedtomaintain.Forexample,theconcentrationofglucoseintheplasmaisabout4-5mmol.l1betweenmeals.Shortlyafterameal,plasmaglucoserisesabovethislevelandthisstimulatesthesecretionofthehor

47、moneinsulinbythepancreas,whichactstobringtheconcentrationdown.Astheconcentrationofglucosefalls,sodoesthesecretionofinsulin.Ineachcase,thechangesinthecirculatinglevelofinsulinacttomaintaintheplasmaglucoseatanappropriatelevel.Thistypeofregulationisknownasnegativefeedback.Duringtheperiodofinsulinsecret

48、ion,theglucoseisbeingstoredaseitherglycogenorfat.22. 負(fù)反饋環(huán)是在機(jī)體出現(xiàn)紊亂時，將一些變量控制在限定范圍內(nèi)的一個控制系統(tǒng)。雖然上面的例子講到血糖，但這一基本原則可以應(yīng)用到其它生理變量中如體溫、血壓和血漿的滲透濃度。負(fù)反饋環(huán)需要一種能對不確定的變量做出反應(yīng)而對其它生理變量不應(yīng)答的傳感器。因此，滲透壓感受器應(yīng)該能對機(jī)體體液滲透的變化而不是體溫和血壓的變化產(chǎn)生應(yīng)答。感受器傳遞的信息必須和理想水平（系統(tǒng)的調(diào)定點(diǎn)）以比較者的身份，以某種方式進(jìn)行比較。如果兩者不相符，一個錯誤信號就會傳遞給效應(yīng)器，效應(yīng)器是一種能使變量保持在理想水平的系統(tǒng)。負(fù)反饋的這些特

49、點(diǎn)可以通過檢測一種簡單的加熱系統(tǒng)來理解。被控制的變量是室溫，它可以由一個溫度計(jì)檢測到，效應(yīng)器是一種加熱器。當(dāng)室溫降低到調(diào)定點(diǎn)以下時，溫度計(jì)就可以監(jiān)測到溫度的變化而開啟加熱器，對室內(nèi)進(jìn)行加溫，直到室溫升高到先前調(diào)好的調(diào)定點(diǎn)，加熱器關(guān)閉。23. anegativefeedbackloopisacontrolsystemthatactstomaintainthelevelofsomevariablewithinagivenrangefollowingadisturbance.Althoughtheexamplegivenabovereferstoplasmaglucose,thebasicprinc

50、iplecanbeappliedtootherphysiologicalvariablessuchasbodytemperature,bloodpressure,andtheosmolalityoftheplasma.anegativefeedbacklooprequiresasensorofsomekindthatrespondstothevariableinquestionbutnottootherphysiologicalbariables,thusanosmoreceptorshouldrespindtochangesinosmolalityofthebodyfluidsbutnott

51、ochangesinbodytemperatureorbloodpressure.theinformationfromthesensormustbecomparedinsomewaywiththedesiredlevelbysomeformofcomparator.ifthetwodonotmatch,anerrorsignalistransmittedtoaneffector,asystemthatcanacttorestorethevariabletoitsdesiredlevel.thesefeaturesofnegativefeedbackcanbeappreciatedbyexami

52、ningasimpleheatingsystem.thecontrolledvariableisroomtemperature,whichissensedbyathermostat.theeffectorisaheaterofsomekind.whentheroomtemperaturefallsbelowthesetpoint,thetemperaturedifferenceisdetectedbythethermostatwhichswitchesontheheater.thisheatstheroomuntilthetemperaturereachesthepersetlevelwher

53、eupontheheaterisswitchedoff.23.總而言之，機(jī)體實(shí)際上是由100萬億細(xì)胞有序組成了不同的功能結(jié)構(gòu)，其中一些被稱為器官。每個功能結(jié)構(gòu)都在維持細(xì)胞外液穩(wěn)態(tài)方面發(fā)揮其作用，這稱之為內(nèi)環(huán)境。只要內(nèi)部環(huán)境處于正常狀態(tài)，機(jī)體細(xì)胞繼續(xù)生存并正常運(yùn)行。每個細(xì)胞都從穩(wěn)態(tài)中獲益，反過來，每個細(xì)胞都為穩(wěn)態(tài)做出貢獻(xiàn)。這種相互作用促使機(jī)體持續(xù)自主運(yùn)行，直至一個或多個功能系統(tǒng)不能正常運(yùn)轉(zhuǎn)。此時，機(jī)體所有細(xì)胞都會受損。功能極度異常會導(dǎo)致死亡，輕微的功能異常導(dǎo)致疾病的發(fā)生。23.Tosumarize,thebodyisactuallyasocialorderofabout100trillionce

54、llsorganizedintodifferentfunctionalstructures,someofwhicharecalledorgans.eachfunctionalstructuresitssharetothemaintenanceofhomeostaticconditionsintheextracellularfluid,whichiscalledtheinternalenvironment.aslongasnormalconditionsaremaintainedinthisinternalenvironment,thecellsofthebodycontinuetolivean

55、dfunctionproperly.Eachcellbenefitsfromhomeostasis,andinturn,eachcellcontributesitssharetowardthemaintenanceofhomeostasis.Thisreciprocalinterplayprovidescontinuousautomaticityofthebodyuntiloneormorefunctionalsystemslosetheirabilitytocontributetheirshareoffunction.Whenthishappens,allthecellsofthebodys

56、uffer.Extremedysfunctionleadstodeath;moderatedysfunctionleadstosickness.1 .心動周期是一次心跳中的一系列活動。心動周期最簡單的形式就是,是兩個心房的同時收縮,緊隨其后，兩個心室同時進(jìn)行收縮。但是,血液從心房進(jìn)入心室和從心室進(jìn)入動脈這兩個過程之間有很大的差別。Thecardiaccycleisthesequenceofeventsinoneheartbeat.Initssimplestform,thecardiaccycleisthesimultaneouscontractionofthetwoatria,followed

57、afractionofasecondlaterbythesimultaneouscontractionofthetwoventricles.Thereis,however,asignificantdifferencebetweenthemovementofbloodfromtheatriatotheventricles,andthemovementofbloodfromtheventriclestothearteries.2 .血液不間斷地從靜脈流入兩個心房。隨著大量的血液積聚,血液的壓力會打開左右房室瓣。兩個心房里三分之二的血液被動地流入到心室中;然后，心房收縮將剩余血液泵入心室。Blood

58、isconstantlyflowingfromtheveinsintobothatria.Asmorebloodaccumulates,itspressureforcesopentherightandleftAVvalves.Twothirdsoftheatrialbloodflowspassivelyintotheventricles;theatriathencontracttopumptheremainingbloodintotheventricles.3 .心房收縮后舒張，心室開始收縮。心室的收縮使血液施壓于左右房室瓣的皮瓣并使其閉合;同時，血液之力也打開了動脈和肺的半月瓣。隨著心室的繼續(xù)收縮,它們把血液射入動脈。注意，進(jìn)入動脈的血液必須被全部泵出。然后心室舒張,同時血液繼續(xù)流入心房，循環(huán)重新開始。Followingtheircontraction,theatriarelaxandtheventriclesbe