1、Body Temperature and Metabolism,sweat,Shiver,Body Temperature and Metabolism,1.1 heat production 1.2 Heat loss 1.3 Regulation of temperature,2.1 The definition of metabolism 2.2 Metabolic rate,Metabolism,Body Temperature,TEXT Body Temperature and Metabolism During every moment of our lives, our cell

2、s are breaking down food molecules to obtain ATP for energy-requiring cellular processes. Naturally, we are not aware of the process of cell respiration, 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 very preci

3、sely, even in a wide range of environmental temperatures.,time-consuming effort-requiring,equipment-processing drawings,inspiration,expiration,perpiration,Body Temperature The normal range of human body temperature is 96.5-99.5 F (36-38C), with an average of 98.6 F (37C). Within a 24-hour period, an

4、 individuals temperature fluctuates 1-2 F with the lowest temperatures occurring during sleep.,Fahrenheit/ centigrade,At either end of the age spectrum, however, temperature regulation may not be as precise as it is in older children or younger adults. Infants have more surface area (skin) relative

5、to volume, and are likely to lose heat more rapidly. In the elderly, the mechanisms that maintain body temperature may not function as efficiently as they once did, and changes in environmental temperature may not be compensated for as quickly or effectively. This is especially important to remember

6、 when caring for patients who are very young or very old.,Heat Production Cell respiration, the process that releases energy from food to produce ATP, also produces heat as one of its energy products. Although cell respiration takes place constantly, there are many factors that influence the rate of

7、 this process:,1. The hormone thyrxine (甲狀腺素and T3), produced by the thyroid gland, increases the rate of cell respiration and heat production. The secretion of thyroxine is regulated by the bodys rate of energy production, the metabolic rate, itself. When the metabolic rate decreases, the thyroid g

8、land is stimulated to secrete more thyroxine.,甲狀腺峽部,As thyroxine increases the rate of cell respiration, a negative 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

9、 the most important regulator of day-to-day energy production. 2. In stress situations, epinephrine and norepinephrine are secreted by the adrenal medulla, and the sympathetic nervous system becomes more active.,Epinephrine increases the rate of cell respiration, especially in organs such as the hea

10、rt, skeletal muscles, and liver. Sympathetic stimulation 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 active (producing ATP) are significant sources of

11、heat when the body is at rest. The skeletal muscles, for example, are usually in a state of slight contraction called muscle tone.,Since even slight contraction requires ATP, the muscles are also producing heat. This amounts to about 25% of the total body heat at rest, and much more during exercise

12、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 rest.,The heat produced by these active organs is dispersed throughout the body by the blo

13、od. As the relatively cooler blood flows through organs such as the muscles and liver, the heat they produce is transferred to the blood, warming it. The warmed blood circulates to other areas of the body, distributing this heat.,distribute handbills,4. The intake of food also increases heat product

14、ion, because the metabolic activity of the digestive tract is increased. Heat is generated as the digestive organs produce ATP for peristalsis and for the synthesis of digestive enzymes. 5. Changes in body temperature also have an effect on metabolic rate and heat production. This becomes clinically

15、 important when a person has a fever, an abnormally high body temperature.,clinical medical college,The higher temperature increases the metabolic rate, which increases heat production and elevates body temperature further. Thus, a high fever may trigger a vicious cycle of ever-increasing heat produ

16、ction.,Heat Loss The pathways of heat loss from the body are the skin, respiratory tract, and to a lesser extent, the urinary and digestive tracts. Heat Loss Through the Skin Since the skin covers the body, most body heat is lost from the skin to the environment. When the environment is cooler than

17、body temperature (as it usually is), heat loss is unavoidable. The amount of heat that is lost is determined by blood flow through the skin and by the activity of sweat glands.,inevitable,Blood flow through the skin influences the amount of heat lost by the processes of radiation, conduction, and co

18、nvection(對流傳熱). Radiation means that heat from the body is lost to cooler air, much as a radiator warms the air within a room. Conduction is the loss of heat to cooler objects, such as clothing, that touch the skin. Convection means that air currents move the warmer air away from the skin surface an

19、d facilitate the loss of heat; this is why a fan makes us feel cooler on hot days.,Convection is the flow of heat through a bulk, macroscopic movement of matter from a hot region to a cool region, as opposed to the microscopic transfer of heat between atoms involved with conduction.,The temperature

20、of the skin and the subsequent loss of heat are determined by blood flow through the skin. The arterioles in the dermis may constrict or dilate to decrease or increase blood flow. Vasoconstriction decreases blood flow through the dermis, and thereby decreases heat loss. Vasodilation in the dermis in

21、creases blood flow to the body surface and loss of heat to the environment.,Squeeze or expand,vasoconstriction,vasodilation,The other mechanism by which heat is lost from the skin is sweating. The eccrine sweat glands secrete sweat (water) onto the skin surface, and excess body heat evaporates the s

22、weat. Think of running water into a hot frying pan; the pan is rapidly cooled as its heat vporizes the water. Although sweating is not quite as dramatic (no visible steam), the principle is just the same.,Sweating is most efficient when the humidity of the surrounding air is low. Humidity is the per

23、centage of the maximum amount of water vapor the atmosphere can contain. A humidity reading of 90% means that the air is already 90% saturated with water vapor and can hold little more. In such a situation, sweat does not readily evaporate, but rather, remains on the skin even as more sweat is secre

24、ted. 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 does have a disadvantage in that it requires the loss of water in orde

25、r to also lose heat. Water loss during sweating may rapidly lead to dehydration, and the water lost must be replaced by drinking fluids.,compensated,Small amounts of heat are also lost in what is called “insensible water loss”. Since the skin is not like a plastic bag, but is somewhat permeable to w

26、ater, 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.,不顯性失水,小散熱源,Heat Loss Through the Respiratory Tract Heat is lost from the respiratory tract as the warmth of the respiratory muc

27、osa evaporates some water from the living epithelial surface. The water vapor formed is exhaled, and a small amount of heat is lost.,mucosae,epithelium,inhale,Animals such as dogs that do not have numerous sweat glands often “pant” in warm weather. Panting is the rapid movement of air into and out o

28、f the upper respiratory passages, where the warm surfaces evaporate large amounts of water. In this way the animal may lose large amounts of heat.,A panting dog,considerable,Heat Loss Through the Urinary and Digestive Tracts When excreted, urine and feces are at body temperature, and their eliminati

29、on results in a very small amount of heat loss. Regulation of Body Temperature The hypothalamus is responsible for the regulation of body temperature, and is considered the “thermostat” of the body. As the thermostat, the hypothalamus maintains the “setting” of body temperature by balancing heat pro

30、duction 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 and about the environmental temperature. Specialized neurons of the hypothalamus detect changes in the temperature of the blood that flo

31、ws through the brain.,The temperature receptors in the skin provide information about the external temperature changes the body is exposed to. The hypothalamus then integrates this sensory information and promotes the necessary responses to maintain body temperature within the normal range. 皮膚溫度感受器負

32、責提供肌體接觸到外部溫度變化的信息，接著下丘腦將感官信息整合，為使體溫維持在正常范圍進行必要的反應。,Mechanisms to Increase Heat Loss In a warm environment or during exercise, the body temperature tends to rise, and greater heat loss is needed. This is accomplished by vasodilation in the dermis and an increase in sweating. Vasodilation brings more

33、warm blood close to the body surface, and heat is lost to the environment. However, if the environmental 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

34、 mentioned previously, sweating becomes inefficient when the atmospheric humidity is high.,On hot days, heat production may also be decreased by a decrease in muscle tone. This is why we may feel very sluggish on hot days; our muscles are even less slightly contracted than usual, and are slower to r

35、espond. Mechanisms to Conserve Heat In a cold environment, heat loss from the body is unavoidable, but may be minimized to some extent. Vasocontriction in the dermis shunts blood away from the body surface, so that more heat is kept in the core of the body. Sweating decreases, and will stop complete

36、ly if the temperature of the hypothalamus falls below about 98.6F.,maximise,If these mechanisms are not sufficient to prevent the body temperature from dropping, more heat may be produced by increasing muscle tone. When this greater muscle tone becomes noticeable and rhythmic it is called shivering,

37、 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 reflect our awareness of the discomfort of being cold. For people (we do not have

38、thick fur as some other mammals), these voluntary activities are of critical importance to the prevention of excessive heat loss when it is very cold.,Metabolism The term metabolism encompasses all the reactions that take place in the body. Everything that happens within us is part of our metabolism

39、. The reactions of metabolism may be divided into two major categories: anabolism and catabolism. Anabolism means synthesis or “formation” reactions, the bonding together of smaller molecules to form larger ones. The synthesis of hemoglobin by cells of the red bone marrow, synthesis of glycogen by,L

40、ife without an aim is like sailing without a compass.,erythro,liver cells, and synthesis of fat to be stored in adipose tissue are all examples of anabolism. Such reactions require energy, usually in the form of ATP. Catabolism means decomposition, the breaking of bonds of larger molecules to form s

41、maller molecules. Cell respiration is a series of catabolic reactions that break down food molecules to carbon dioxide and water. During catabolism, energy is often released and used to synthesize ATP. The ATP formed during catabolism is then used for energy-requiring anabolic reactions.,Most of our

42、 anabolic and catabolic reactions are catalyzed by enzymes. Enzymes are proteins that enable reactions to take place rapidly at body temperature. The body has thousands of enzymes, and each is specific, that is, will catalyze only one type of reaction. Metabolic Rate Although the term metabolism is

43、used to describe all of the chemical reactions that take place within the body, metabolic rate is usually expressed as an amount of heat production.,This is because many body processes that utilize ATP also produce heat. These processes include the contraction of skeletal muscle, the pumping of the

44、heart, and the normal breakdown of cellular components. Therefore, it is possible to quantify heat production as a measure of metabolic activity. Generally, the energy available from food is measured in kilocalories (kcal). Kilocalories are also the units used to measure the energy expended by the b

45、ody.,utility,During sleep, for example, energy expended by a 150-pound person is about 60 to 70 kcal per hour. Getting up and preparing breakfast increases energy expenditure 80 to 90 kcal per hour. For mothers with several small children, this value may be significantly higher. Clearly, greater act

46、ivity results in greater energy expenditure. The energy required for merely living (lying quietly in bed) is the basal metabolic rate (BMR). There are a number of factors that affect the metabolic rate of an active person.,1. ExerciseContraction of skeletal muscle increases energy expenditure and ra

47、ises metabolic rate. 2. AgeMetabolic rate is highest in young children and decreases with age. The energy requirements for growth and the greater heat loss by a smaller body contribute to the higher rate in children. After growth has stopped, metabolic rate decreases about 2% per decade. If a person becomes less active, the total decrease is almost 5% per decade.,3. Body Configuration of AdultsTall, thin people usually have higher metabolic rates than do short, stocky people of the same wei