医学英语emeraure课件.pptx

1、sweatShiverShiver4 parts1.1 heat 1.1 heat productionproduction1.2 Heat loss1.2 Heat loss1.3 Regulation of 1.3 Regulation of temperaturetemperature2.1 The 2.1 The definition of definition of metabolismmetabolism2.2 Metabolic 2.2 Metabolic raterateMetabolismMetabolismBody TemperatureBody TemperatureTE

2、XTTEXT Body Temperature and Metabolism Body Temperature and Metabolism During every moment of our lives,our cells are breaking downbreaking down food molecules to obtain ATP for energy-requiring cellular processes.Naturally,we are not aware of are not aware of the process of cell respirationcell res

3、piration,but we may be aware of one of the products,energy in the form of heat.The human body is indeed warm,and its temperature is regulated regulated very precisely,even in a wide range ofin a wide range of e n v i r o n m e n t a l t e m p e r a t u r e s.time-consuming effort-time-consuming effo

4、rt-requiringrequiringequipment-processing drawingsequipment-processing drawingsinspirationinspirationexpirationexpirationperpirationperpirationBody TemperatureBody Temperature T h e n o r m a l range of human body t e m p e r a t u r e i s 96.5-99.5 F(36-3 8 C),w i t h a n average of 98.6 F(37C).Wit

5、hin a 24-hour period,an i n d i v i d u a l s t e m p e r a t u r e fluctuatesfluctuates 1-2 F with the lowest t e m p e r a t u r e s occurring during sleep.Fahrenheit/Fahrenheit/centigradecentigrade At either end of the age spectrumspectrum,however,temperature regulation may not be as precisepreci

6、se as it is in older childrenolder children or younger adultsyounger adults.Infants have more surface area(skin)relative to volume,and are likely to lose heat more rapidly.In the elderly,the mechanisms that maintain body temperature may not function as efficientlyefficiently as they once did,and cha

7、nges in environmental temperature may not be compensated forcompensated for as quickly or effectively.This is especially important to remember when caring for patients who a r e v e r y y o u n g o r v e r y o l d.Heat ProductionHeat Production Cell respiration,the process that releases energy from

8、food to produce ATP,also produces heat as one of its energy products.Although cell respiration takes place constantlyconstantly,there are many factors that influence the rate of this process:1.The hormone thyrthyrxinexine(甲状腺素and T3),produced by the thyroid gland,increases the rate of cell respirati

9、on and heat production.The secretion of thyroxine is regulatedregulated by the b o d y s r a t e o f e n e r g y production,the metabolic ratemetabolic rate,itself.When the metabolic rate decreases,the thyroid gland is stimulated to secrete more thyroxine.甲状腺峡部 As thyroxine increases the rate of cel

10、l respiration,a negative feedbacknegative feedback mechanism inhibits further secretion until metabolic rate decreases again.Thus,thyroxine is secreted whenever there is a need for increased cell respiration,and is probably the most important regulator regulator of day-to-dayday-to-day energy produc

11、tion.2.In stress situations,epinephrineepinephrine and norepinephrinenorepinephrine are secreted by the adrenal medullaadrenal medulla,and the sympathetic sympathetic nervous systemnervous system becomes more active.Epinephrine increases the rate of cell respiration,especially in organs such as the

12、heart,skeletal skeletal musclesmuscles,and liver.Sympathetic Sympathetic stimulationstimulation also increases the activity of these organs.The increased production of ATP to meet the demands of the stress situation also means that more heat will be produced.3.Organs that are normally a c t i v e (p

13、 r o d u c i n g A T P)a r e significant sources of heat when the body is at restat rest.The skeletal muscles,for example,are usually in a state of slight contraction called muscle muscle tonetone.Since even slightslight contraction requires ATP,the muscles are also producing heat.This amounts toamo

14、unts to about 25%of the total body heat at rest,and much more during exerciseduring exercise when more ATP is produced.The liver is another organ that is continually active,producing ATP to supply energy for its many functions.As a result,the liver produces as much as 20%of the total body heat at re

15、st.The heat produced by these active organs is disperseddispersed throughout the body by the blood.As the relatively cooler blood flowsflows through organs such as the muscles and liver,the heat they produce is transferredtransferred to the blood,w a r m i n g i t.T h e w a r m e d b l o o d circula

16、tescirculates to other areas of the body,d i s t r i b u t i n gd i s t r i b u t i n g t h i s h e a t.distribute handbillsdistribute handbills 4.The intakeintake of food also increases heat production,because the metabolic activity of the digestive tractdigestive tract is increased.Heat is generat

17、edgenerated as the digestive organs produce ATP for peristalsisperistalsis and for the synthesis of d i g e s t i v e e n z y m e sd i g e s t i v e e n z y m e s.5.Changes in body temperature also have an effect on metabolic rate and heat production.This becomes clinicallyclinically important when

18、a person has a fever,an abnormallyabnormally high body temperature.clinical medical collegeclinical medical collegeThe higher temperature increases the metabolic rate,which increases heat production and elevates elevates body temperature further.Thus,a high fever may trigger trigger a vicious cyclev

19、icious cycle of ever-increasing heat production.Heat LossHeat Loss The pathwayspathways of heat loss from the body are the skin,respiratory tract,and to a to a lesser extentlesser extent,the urinaryurinary and digestive tracts.Heat Loss Through the SkinHeat Loss Through the Skin Since the skin cover

20、s the body,most body heat is lost from the skin to the environment.When the environment is cooler than body temperature(as it usually is),heat loss is unavoidableunavoidable.The amount of heat that is lost is determined by blood flow through the skin and by the activity of sweat glands.inevitableine

21、vitable Blood flow through the skin influences the amount of heat lost by the processes of radiationradiation,conduction,conduction,and convectionconvection(对流传热).Radiation means that heat from the body is lost to cooler air,much as a radiatorradiator warms the air within a room.Conduction is the lo

22、ss of heat to cooler objects,such as clothingclothing,that touch the skin.Convection means that air currentsair currents move the warmer air away from the skin surface and facilitate the loss of heat;this is why a fanfan makes u s f e e l c o o l e r o n h o t d a y s.ConvectionConvection is the flo

23、w of heat through a bulk,macroscopic movement of matter from a hot region to a cool region,as o p p o s e d t o t h e microscopic transfer o f h e a t b e t w e e n atoms involved with c o n d u c t i o n.The temperature of the skin and the s u b s e q u e n ts u b s e q u e n t loss of h e a t a r

24、e determined by blood flow through the skin.The arteriolesarterioles in the dermisdermis may constrictconstrict or dilate dilate to decrease o r i n c r e a s e b l o o d f l o w.Vasoconstriction decreases blood flow through the dermis,and thereby decreases heat loss.Vasodilation in the dermis incre

25、ases blood flow to the body surface and loss of heat to t h e e n v i r o n m e n t.Squeeze or expandvasoconstrictionvasodilation The other mechanism by which heat is lost from the skin is sweatsweating.The eccrineeccrine sweat glands secrete sweat(water)onto the skin surface,and excess body heat ev

26、aporatesevaporates the sweat.Think of running water into a hot frying pan;the pan is rapidly cooled as its heat vporizesvporizes the water.Although sweating is not quite as dramaticdramatic(no visible steam),the p r i n c i p l e i s j u s t t h e s a m e.Sweating is most efficient when the humidity

27、humidity of the surrounding air is low.Humidity is the percentage of the maximum amount of water vapor the atmosphere can contain.A humidity reading of 90%means that the air is already 90%saturatedsaturated with water vapor and can hold little more.In such a situation,sweat does not readily evaporat

28、e,but rather,remains on the skin even as more sweat is secreted.If the humidity is 40%,however,the air can hold a great deal more water vapor,and sweat evaporates quickly from the skin surface,removing excess body heat.Although sweating is a very effective mechanism of heat loss,it doesdoes have a d

29、isadvantage in that it requires the loss of water in order to also lose heat.Water loss during sweating may rapidly lead to lead to dedehydrationhydration,and the water lost must be replaced by drinking pensatedcompensated Small amounts of heat are also lost in what is called“insensible insensible w

30、ater losswater loss”.Since the skin is not like a plastic bag,but is somewhat permeable to water,a small amount of water diffuses through the skin and is evaporated by body heat.Compared to sweating,however,insensible water loss is a minor source of heat loss.不显性失水小散热源THANK YOUSUCCESS2022-10-1331可编辑

31、Heat Loss Through the Respiratory Heat Loss Through the Respiratory TractTract Heat is lost from the respiratory t r a c t a s t h e w a r m t h o f t h e respiratory mucosamucosa evaporates some water from the living epiepithelialthelial surface.The water vapor formed is exhaledexhaled,and a small

32、amount of heat is lost.mucosaemucosaeepitheliumepitheliuminhaleinhale Animals such as dogs that do not have numerousnumerous sweat glands often“pantpant”in warm weather.Panting is the rapid movement of air into and out o f t h e u p p e r respiratory passages,w h e r e t h e w a r m surfaces evapora

33、te large amounts of water.In this way the animal may lose large amounts oflarge amounts of heat.A panting dogA panting dogconsiderablconsiderable eHeat Loss Through the Urinary and Heat Loss Through the Urinary and Digestive TractsDigestive Tracts When excretexcreted,urine and feces are at body temp

34、erature,and their eliminationelimination results in a very small amount of heat loss.Regulation of Body TemperatureRegulation of Body Temperature The hypothalamushypothalamus is responsible for the regulation of body temperature,and is considered the“thermostatthermostat”of the body.As the thermosta

35、t,the hypothalamus maintains the“setting”of body temperature by balancing heat production and heat loss to keep the body at the set temperature.In order to do this,the hypothalamus must receive information about the temperature within the body a n d a b o u t t h e e n v i r o n m e n t a l temperat

36、ure.SpecializedSpecialized neuronsneurons of the hypothalamus detectdetect changes in the temperature of the blood that f l o w s t h r o u g h t h e b r a i n.The temperature receptors in the skin provide information about the external temperature changes the body is exposed is exposed toto.The hyp

37、othalamus then integrateintegrates this sensory information and promotepromotes the necessary responses to maintain body temperature within the normal range.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。Mechanisms to Increase Heat LossMechanisms to Increase Heat Loss In a warm environmen

38、t or during exercise,the body temperature tends to rise,and greater heat loss is needed.This is accomplishaccomplished by vasodilation in the dermis and an increase in sweating.Vasodilation brings more warm blood close to the body surface,and heat is lost to the environment.However,if the environmen

39、tal temperature is higher than body temperature,this mechanism becomes ineffective.The second mechanism is increased sweating,in which excess body heat evaporates the sweat on the skin surface.As mentioned previously,sweating becomes inefficient when the atmospheric atmospheric humidityhumidity is h

40、igh.On hot days,heat production may also be decreased by a decrease in muscle tone.This is why we may feel very sluggishsluggish on hot days;our muscles are even less slightly contracted than usual,and are s l o w e r t o r e s p o n d.Mechanisms to Conserve HeatMechanisms to Conserve Heat In a cold

41、 environment,heat loss from the body is unavoidable,but may be minimizedminimized to some extent.Vasocontriction in the dermis shunts shunts blood away from the body surface,so that more heat is kept in the core core of the body.Sweating decreases,and will stop completely if the temperature of the h

42、ypothalamus fallfalls b e l o w a b o u t 9 8.6 F.maximisemaximise If these mechanisms are not sufficientsufficient to prevent the body temperature from dropdropping,more heat may be produced by increasing muscle tone.When this greater muscle tone becomes noticeable and rhythmic it is called shiveri

43、ng,and may increase heat production as much as five times the normal.People also have behavioral responses to cold,and these too are important to prevent heat loss.Such things as putting on a sweater or going indoors r e f l e c tr e f l e c t our awareness of the discomfort of being cold.For people

44、(we do not have thick fur as some other mammals),these voluntaryvoluntary activities are of critical importance to the prevention of excessive heat l o s s w h e n i t i s v e r y c o l d.MetabolismMetabolism The term metabolism encompassencompasses all the reactions that take place in the body.Ever

45、ything that happens within us is part of our metabolism.The reactions of metabolism may be divided into two major categories:anabolismanabolism and catabolismcatabolism.Anabolism means synthesissynthesis or“formation”reactions,the bonding together of smaller molecules to form larger ones.The synthes

46、is of hemoglobinhemoglobin by cells of the red bone marrowred bone marrow,synthesis of glycogenglycogen byLife without an aim is like sailing without a compass.erythroliver cells,and synthesis of fat to be stored in adiposeadipose tissuetissue are all examples of anabolism.Such reactions require ene

47、rgy,usually in the form of ATP.Catabolism means decompositiondecomposition,the breaking of bonds of larger molecules to form smaller molecules.Cell respiration is a series of catabolic reactions that break break downdown food molecules to carbon dioxide and water.During catabolism,energy is often re

48、leased and used to synthesize ATP.The ATP formed during catabolism is then used for energy-requiring anabolic reactions.Most of our anabolic and catabolic reactions are catalyzedcatalyzed by enzymes.Enzymes are proteins that enable reactions to take place rapidly at body temperature.The body has tho

49、usands of enzymes,and each is specificspecific,that is,will catalyzecatalyze only one type of reaction.Metabolic RateMetabolic Rate Although the term metabolism is used to describe all of the chemical reactions that take place within the body,metabolic rate is usually expressed as an amount of heat

50、production.This is because many body processes that utilizeutilize ATP also produce heat.These processes include the contraction of skeletal muscle,the pumping of the heart,and the normal breakdownbreakdown of cellular components.Therefore,it is possible to quantifyquantify heat production as a meas