Energy Metabolism and. Body Temperature

Transcription

1 Energy Metabolism and Body Temperature Liang Huawei, Ph.D.

2 Energy metabolism 能量代谢 The metabolic processes by which energy is made available for the use of the body

3 Energy sources 能量的来源 Carbohydrates - mainly glucose 65 % of the total energy Glycolysis ( 糖酵解 ) and citric acid cycle

4 Fat fatty acids The storage of fat in the body is much greater than that of glucose The energy liberated by oxidation of 1 g of fat is 2 times that produced by the same amount of glucose

5 Proteins The amount of energy provided by proteins is relatively small in human being Protein will become the major energy source to maintain the essential vital activities in special conditions

6 Energy transfer and utilization 能量的转移和利用 ATP: Energy Currency ATP is generated by combustion of carbohydrates, fats and proteins Energy from ATP can be used by the cells Synthesis and growth Muscular contraction Glandular secretion Nerve conduction Active absorption

7 Phosphocreatine ( 磷酸肌酸 ): an ATP buffer

8 Heat is the end product of almost all the energy released in the body

9 Obesity 肥胖 Energy intake > energy expenditure

10 Measurement of Energy Metabolism 能量代谢的测定 Metabolic rate Metabolism per unit time especially as estimated by food consumption, energy released as heat, or oxygen used in metabolic processes Method Direct Calorimetry 直接测热法 Indirect Calorimetry 间接测热法

11 Direct Calorimetry 直接测热法

12 Indirect Calorimetry 间接测热法 - Estimation of the heat produced by means of the respiratory differences of oxygen and carbon dioxide in the inspired and expired air C 6 H 12 O 6 + 6O 2 = 6CO 2 + 6H 2 O + ΔH Thermal equivalent of food ( 食物的热价 ):kcal/g (kj/g) Physical thermal equivalent ( 物理热价 ) Biological thermal equivalent ( 生物热价 ) Protein: Biological thermal equivalent < Physical thermal equivalent

13 Energy equivalent of oxygen 食物的氧热价 Heat production by consuming one litre of oxygen to oxidize a specific type of food Respiratory quotient (RQ) 呼吸商 The ratio of the volume of CO 2 produced to volume of O 2 consumed when a type of food is oxidized

14 The Caloric Values of Foods and the Relative Data Food Heat Production (kj/g) Physical Biological Calorie Calorie Consumption of O 2 (L/g) Production of CO 2 (L/g) Thermal equivalent of oxygen (kj/g) Respiratory quotient (RQ) Glucose Protein Fat

15 Energy metabolic rate = thermal equivalent of oxygen oxygen consumption

16 Methods of measuring CO 2 production and O 2 consumption Open circuit method Closed circuit method

17 Closed circuit method

18 Factors that affect energy metabolic rate 影响能量代谢的主要因素 Physical Activities 肌肉活动 Form of Activity Heat Output (kj/m 2 /min) Awake lying still Sitting at rest Cleaning the window Washing clothes Cleaning the floor Playing volleyball Playing basketball Playing football

19 Psychic activity 精神活动

20 Thermogenic effect of food -Specific Dynamic Action of food 食物的特殊动力效应 to refer to the way that the foods you eat can increase the amount of heat your body generates as it digests them, resulting in an increased metabolism for a short amount of time

21 Environmental temperature 环境温度 20 C - 30 C Cold stress Shivering thermogenesis Non-shivering thermogenesis

22 Basal Metabolism 基础代谢 Basal metabolic rate (BMR) 基础代谢率 The minimum energy expenditure for the body to exist 50-70% of the daily energy expenditure BMR is usually expressed as Calories per hour per square meter of body surface area

23 Method for determining BMR 基础代谢率的测定方法 To measure the rate of O 2 utilization under the following conditions Keep fast at least for 12 hours After a night of restful sleep No strenuous activity Eliminated psychic and physical factors that cause excitement No physical activity RT: 20 to 27 C

24 Gender and age Factors that influence the BMR 影响 BMR 的因素

25 Thyroid hormone, male sex hormone, growth hormone and fever BMR Sleep and malnutrition BMR

26 Body Temperature & Temperature Regulation

27 Body temperature 体温 Shell temperature Changing with the temperature of the surroundings Core temperature Maintaining constant (when T=13~54 C)

28 Normal Core temperature Site Mean Value of Temperature Standard Deviation Range of Variation of Temperature Axilla o C o C Oral cavity o C o C Rectum o C o C

29 Physiological fluctuations of the body temperature 体温的生理性波动 Circadian rhythm 昼夜节律 Diurnal rhythmic changes with a variation of 1 C Sex difference in body temperature

30 Age Emotional stress Muscle activity Food, drugs

31 Temperature Regulation 体温的调节 Body temperature is controlled by balancing heat production against heat loss

32 Heat production 机体的产热 Major organs of heat production in the body Percentage in Body Weight Percentage at Rest Heat-production During Labor The Brain The Internal Organs (i.e. Liver and Spleen, etc.) The muscle & Skin The Others

33 Modes of heat-production 产热方式 Shivering thermogenesis 战栗产热 Non-shivering thermogenesis Control of thermogenesis Thyroxine, catecholamines, androgens and GH Sympathetic nervous system

34 Heat Loss 机体的散热 By the skin By expiration, urination, and defecation By panting

35 How is heat lost from the skin surface? Radiation 辐射 : 60% Infrared heat rays

36 Conduction 传导 Conduction to solid objects Conduction to air Effect of clothing on conductive heat loss

37 Convection 对流 Cooling effect of wind

38 Evaporation 蒸发 A necessary cooling mechanism at very high air temperature 0.58 Calorie of heat is lost for 1 g water that evaporates

39 Evaporation Insensible perspiration 不感蒸发 ml H 2 O/day Sweating 发汗 Sweat gland Cholinergic sympathetic nerve innervation

40 Control of heat loss By regulation of skin blood flow By regulation of sweat glands

41 Regulation of Body Temperature The temperature of the body is regulated almost entirely by nervous feedback mechanisms Behavioral control of body temperature

42 Temperature receptors 温度感受器 Temperature receptors in the skin Warmth receptors Cold receptors: more Deep body temperature receptors Spinal cord, abdominal viscera, great veins

43 Anterior hypothalamic-preoptic area (AH/PO) Cold-sensitive neurons Heat-sensitive neurons Serve as a thermostatic body temperature control center

44 Temperature-regulating centers In the hypothalamus Preoptic and anterior hypothalamic (PO/AH) region 视前区 - 下丘脑前部

45 Set point 调定点 The level or point at which a variable physiological state (as body temperature) tends to stabilize PO/AH

46 Neuronal effector mechanisms that decrease or increase body temperature Temperature-decreasing mechanisms when the body is too hot Vasodilatation Sweating Decrease in heat production

47 Neuronal effector mechanisms that decrease or increase body temperature Temperature-increasing mechanisms when the body is too cold Skin vasoconstriction Increase in heat production Shivering (primary motor center for shivering in hypothalamus) Sympathetic excitation Thyroxine (Eskimos -- higher incidence of toxic thyroid goiters)

48 Regulation of Body Temperature

49 Regulation of Body Temperature

50 Abnormalities of body temperature regulation Fever 发热 Pyrogens 致热原 Increasing set-point Heatstroke 中暑 BT: o C A cold water bath Sponge or spray cooling of the skin

51 Summary Terms Respiratory quotient Specific dynamic action of food Basal metabolic rate Body temperature Set-point List the factors that affect energy metabolic rate Describe the modes of heat-loss from the skin

52 General Question How dose the body actively maintain a constant body temperature despite changes in ambient temperature?

53 Thank You!