医学英语课件Temperature.pptVIP

BodyTemperatureandMetabolism sweat Shiver BodyTemperatureandMetabolism 1 1heatproduction1 2Heatloss1 3Regulationoftemperature 2 1Thedefinitionofmetabolism2 2Metabolicrate Metabolism BodyTemperature TEXTBodyTemperatureandMetabolismDuringeverymomentofourlives ourcellsarebreakingdownfoodmoleculestoobtainATPforenergy requiringcellularprocesses Naturally wearenotawareoftheprocessofcellrespiration butwemaybeawareofoneoftheproducts energyintheformofheat Thehumanbodyisindeedwarm anditstemperatureisregulatedveryprecisely eveninawiderangeofenvironmentaltemperatures time consumingeffort requiring equipment processingdrawings inspiration expiration perpiration BodyTemperatureThenormalrangeofhumanbodytemperatureis96 5 99 5 F 36 38 C withanaverageof98 6 F 37 C Withina24 hourperiod anindividual stemperaturefluctuates1 2 Fwiththelowesttemperaturesoccurringduringsleep Fahrenheit centigrade Ateitherendoftheagespectrum however temperatureregulationmaynotbeaspreciseasitisinolderchildrenoryoungeradults Infantshavemoresurfacearea skin relativetovolume andarelikelytoloseheatmorerapidly Intheelderly themechanismsthatmaintainbodytemperaturemaynotfunctionasefficientlyastheyoncedid andchangesinenvironmentaltemperaturemaynotbecompensatedforasquicklyoreffectively Thisisespeciallyimportanttorememberwhencaringforpatientswhoareveryyoungorveryold HeatProductionCellrespiration theprocessthatreleasesenergyfromfoodtoproduceATP alsoproducesheatasoneofitsenergyproducts Althoughcellrespirationtakesplaceconstantly therearemanyfactorsthatinfluencetherateofthisprocess 1 Thehormonethyr xine 甲状腺素andT3 producedbythethyroidgland increasestherateofcellrespirationandheatproduction Thesecretionofthyroxineisregulatedbythebody srateofenergyproduction themetabolicrate itself Whenthemetabolicratedecreases thethyroidglandisstimulatedtosecretemorethyroxine 甲状腺峡部 Asthyroxineincreasestherateofcellrespiration anegativefeedbackmechanisminhibitsfurthersecretionuntilmetabolicratedecreasesagain Thus thyroxineissecretedwheneverthereisaneedforincreasedcellrespiration andisprobablythemostimportantregulatorofday to dayenergyproduction 2 Instresssituations epinephrineandnorepinephrinearesecretedbytheadrenalmedulla andthesympatheticnervoussystembecomesmoreactive Epinephrineincreasestherateofcellrespiration especiallyinorganssuchastheheart skeletalmuscles andliver Sympatheticstimulationalsoincreasestheactivityoftheseorgans TheincreasedproductionofATPtomeetthedemandsofthestresssituationalsomeansthatmoreheatwillbeproduced 3 Organsthatarenormallyactive producingATP aresignificantsourcesofheatwhenthebodyisatrest Theskeletalmuscles forexample areusuallyinastateofslightcontractioncalledmuscletone SinceevenslightcontractionrequiresATP themusclesarealsoproducingheat Thisamountstoabout25 ofthetotalbodyheatatrest andmuchmoreduringexercisewhenmoreATPisproduced Theliverisanotherorganthatiscontinuallyactive producingATPtosupplyenergyforitsmanyfunctions Asaresult theliverproducesasmuchas20 ofthetotalbodyheatatrest Theheatproducedbytheseactiveorgansisdispersedthroughoutthebodybytheblood Astherelativelycoolerbloodflowsthroughorganssuchasthemusclesandliver theheattheyproduceistransferredtotheblood warmingit Thewarmedbloodcirculatestootherareasofthebody distributingthisheat distributehandbills 4 Theintakeoffoodalsoincreasesheatproduction becausethemetabolicactivityofthedigestivetractisincreased HeatisgeneratedasthedigestiveorgansproduceATPforperistalsisandforthesynthesisofdigestiveenzymes 5 Changesinbodytemperaturealsohaveaneffectonmetabolicrateandheatproduction Thisbecomesclinicallyimportantwhenapersonhasafever anabnormallyhighbodytemperature clinicalmedicalcollege Thehighertemperatureincreasesthemetabolicrate whichincreasesheatproductionandelevatesbodytemperaturefurther Thus ahighfevermaytriggeraviciouscycleofever increasingheatproduction HeatLossThepathwaysofheatlossfromthebodyaretheskin respiratorytract andtoalesserextent theurinaryanddigestivetracts HeatLossThroughtheSkinSincetheskincoversthebody mostbodyheatislostfromtheskintotheenvironment Whentheenvironmentiscoolerthanbodytemperature asitusuallyis heatlossisunavoidable Theamountofheatthatislostisdeterminedbybloodflowthroughtheskinandbytheactivityofsweatglands inevitable Bloodflowthroughtheskininfluencestheamountofheatlostbytheprocessesofradiation conduction andconvection 对流传热 Radiationmeansthatheatfromthebodyislosttocoolerair muchasaradiatorwarmstheairwithinaroom Conductionisthelossofheattocoolerobjects suchasclothing thattouchtheskin Convectionmeansthataircurrentsmovethewarmerairawayfromtheskinsurfaceandfacilitatethelossofheat thisiswhyafanmakesusfeelcooleronhotdays Convectionistheflowofheatthroughabulk macroscopicmovementofmatterfromahotregiontoacoolregion asopposedtothemicroscopictransferofheatbetweenatomsinvolvedwithconduction Thetemperatureoftheskinandthesubsequentlossofheataredeterminedbybloodflowthroughtheskin Thearteriolesinthedermismayconstrictordilatetodecreaseorincreasebloodflow Vasoconstrictiondecreasesbloodflowthroughthedermis andtherebydecreasesheatloss Vasodilationinthedermisincreasesbloodflowtothebodysurfaceandlossofheattotheenvironment Squeezeorexpand vasoconstriction vasodilation Theothermechanismbywhichheatislostfromtheskinissweating Theeccrinesweatglandssecretesweat water ontotheskinsurface andexcessbodyheatevaporatesthesweat Thinkofrunningwaterintoahotfryingpan thepanisrapidlycooledasitsheatv porizesthewater Althoughsweatingisnotquiteasdramatic novisiblesteam theprincipleisjustthesame Sweatingismostefficientwhenthehumidityofthesurroundingairislow Humidityisthepercentageofthemaximumamountofwatervaportheatmospherecancontain Ahumidityreadingof90 meansthattheairisalready90 saturatedwithwatervaporandcanholdlittlemore Insuchasituation sweatdoesnotreadilyevaporate butrather remainsontheskinevenasmoresweatissecreted Ifthehumidityis40 however theaircanholdagreatdealmorewatervapor andsweatevaporatesquicklyfromtheskinsurface removingexcessbodyheat Althoughsweatingisaveryeffectivemechanismofheatloss itdoeshaveadisadvantageinthatitrequiresthelossofwaterinordertoalsoloseheat Waterlossduringsweatingmayrapidlyleadtodehydration andthewaterlostmustbereplacedbydrinkingfluids compensated Smallamountsofheatarealsolostinwhatiscalled insensiblewaterloss Sincetheskinisnotlikeaplasticbag butissomewhatpermeabletowater asmallamountofwaterdiffusesthroughtheskinandisevaporatedbybodyheat Comparedtosweating however insensiblewaterlossisaminorsourceofheatloss 不显性失水 小散热源 HeatLossThroughtheRespiratoryTractHeatislostfromtherespiratorytractasthewarmthoftherespiratorymucosaevaporatessomewaterfromthelivingepithelialsurface Thewatervaporformedisexhaled andasmallamountofheatislost mucosae epithelium inhale Animalssuchasdogsthatdonothavenumeroussweatglandsoften pant inwarmweather Pantingistherapidmovementofairintoandoutoftheupperrespiratorypassages wherethewarmsurfacesevaporatelargeamountsofwater Inthiswaytheanimalmayloselargeamountsofheat Apantingdog considerable HeatLossThroughtheUrinaryandDigestiveTractsWhenexcreted urineandfecesareatbodytemperature andtheireliminationresultsinaverysmallamountofheatloss RegulationofBodyTemperatureThehypothalamusisresponsiblefortheregulationofbodytemperature andisconsideredthe thermostat ofthebody Asthethermostat thehypothalamusmaintainsthe setting ofbodytemperaturebybalancingheatproductionandheatlosstokeepthebodyatthesettemperature Inordertodothis thehypothalamusmustreceiveinformationaboutthetemperaturewithinthebodyandabouttheenvironmentaltemperature Specializedneuronsofthehypothalamusdetectchangesinthetemperatureofthebloodthatflowsthroughthebrain Thetemperaturereceptorsintheskinprovideinformationabouttheexternaltemperaturechangesthebodyisexposedto Thehypothalamusthenintegratesthissensoryinformationandpromotesthenecessaryresponsestomaintainbodytemperaturewithinthenormalrange 皮肤温度感受器负责提供肌体接触到外部温度变化的信息 接着下丘脑将感官信息整合 为使体温维持在正常范围进行必要的反应 MechanismstoIncreaseHeatLossInawarmenvironmentorduringexercise thebodytemperaturetendstorise andgreaterheatlossisneeded Thisisaccomplishedbyvasodilationinthedermisandanincreaseinsweating Vasodilationbringsmorewarmbloodclosetothebodysurface andheatislosttotheenvironment However iftheenvironmentaltemperatureishigherthanbodytemperature thismechanismbecomesineffective Thesecondmechanismisincreasedsweating inwhichexcessbodyheatevaporatesthesweatontheskinsurface Asmentionedpreviously sweatingbecomesinefficientwhentheatmospherichumidityishigh Onhotdays heatproductionmayalsobedecreasedbyadecreaseinmuscletone Thisiswhywemayfeelverysluggishonhotdays ourmusclesareevenlessslightlycontractedthanusual andareslowertorespond MechanismstoConserveHeatInacoldenvironment heatlossfromthebodyisunavoidable butmaybeminimizedtosomeextent Vasocontrictioninthedermisshuntsbloodawayfromthebodysurface sothatmoreheatiskeptinthecoreofthebody Sweatingdecreases andwillstopcompletelyifthetemperatureofthehypothalamusfallsbelowabout98 6 F maximise Ifthesemechanismsarenotsufficienttopreventthebodytemperaturefromdropping moreheatmaybeproducedbyincreasingmuscletone Whenthisgreatermuscletonebecomesnoticeableandrhythmicitiscalledshivering andmayincreaseheatproductionasmuchasfivetimesthenormal Peoplealsohavebehavioralresponsestocold andthesetooareimportanttopreventheatloss Suchthingsasputtingonasweaterorgoingindoorsreflectourawarenessofthediscomfortofbeingcold Forpeople wedonothavethickfurassomeothermammals thesevoluntaryactivitiesareofcriticalimportancetothepreventionofexcessiveheatlosswhenitisverycold MetabolismThetermmetabolismencompassesallthereactionsthattakeplaceinthebody Everythingthathappenswithinusispartofourmetabolism Thereactionsofmetabolismmaybedividedintotwomajorcategories anabolismandcatabolism Anabolismmeanssynthesisor formation reactions thebondingtogetherofsmallermoleculestoformlargerones Thesynthesisofhemoglobinbycellsoftheredbonemarrow synthesisofglycogenby Lifewithoutanaimislikesailingwithoutacompass erythro livercells andsynthesisoffattobestoredinadiposetissueareallexamplesofanabolism Suchreactionsrequireenergy usuallyintheformofATP Catabolismmeansdecomposition thebreakingofbondsoflargermoleculestoformsmallermolecules Cellrespirationisaseriesofcatabolicreactionsthatbreakdownfoodmoleculestocarbondioxideandwater Duringcatabolism energyisoftenreleasedandusedtosynthesizeATP TheATPformedduringcatabolismisthenusedforenergy requiringanabolicreactions Mostofouranabolicandcatabolicreactionsarecatalyzedbyenzymes Enzymesareproteinsthatenablereactionstotakeplacerapidlyatbodytemperature Thebodyhasthousandsofenzymes andeachisspecific thatis willcatalyzeonlyonetypeofreaction MetabolicRateAlthoughthetermmetabolismisusedtodescribeallofthechemicalreactionsthattakeplacewithinthebody metabolicrateisusuallyexpressedasanamountofheatproduction ThisisbecausemanybodyprocessesthatutilizeATPalsoproduceheat Theseprocessesincludethecontractionofskeletalmuscle thepumpingoftheheart andthenormalbreakdownofcellularcomponents Therefore itispossibletoquantifyheatproductionasameasureofmetabolicactivity Generally theenergyavailablefromfoodismeasuredinkilocalories kcal Kilocaloriesarealsotheunitsusedtomeasuretheenergyexpendedbythebody utility Duringsleep forexample energyexpendedbya150 poundpersonisabout60to70kcalperhour Gettingupandpreparingbreakfastincreasesenergyexpenditure80to90kcalperhour Formotherswithseveralsmallchildren thisvaluemaybesignificantlyhigher Clearly greateractivityresultsingreaterenergyexpenditure Theenergyrequiredformerelyliving lyingquietlyinbed isthebasalmetabolicrate BMR Thereareanumberoffactorsthataffectthemetabolicrateofanactiveperson 1 Exercise Contractionofskeletalmuscleincreasesenergyexpenditureandraisesmetabolicrate 2 Age Metabolicrateishighestinyoungchildrenanddecreaseswithage Theenergyrequirementsforgrowthandthegreaterheatlossbyasmallerbodycontributetothehigherrateinchildren Aftergrowthhasstopped metabolicratedecreasesabout2 perdecade Ifapersonbecomeslessactive thetotaldecreaseisalmost5 perdecade 3 BodyConfigurationofAdults Tall thinpeopleusuallyhavehighermetabolicratesthandoshort stockypeopleofthesameweight Thisissobecausethetall thinpersonhas