一、机体能量的来源和去路 (一)机体能量的来源 主要能源.ppt

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1、Energy and substance flow in creature, Metabolism,Xiao (Gregory) ShenDepartment of Physiology, ZUSM,Catabolism and Anabolism,Catabolism: breaks down large molecules (such as polysaccharides, lipids, nucleic acids and proteins) into smaller units, releasing energy into smaller units (such as monosacc

2、harides, fatty acids, nucleotides, and amino acids).Anabolism: construct molecules from smaller units, requiring energy. Anabolism is powered by catabolism (hydrolysis of adenosine triphosphate (ATP).,Part I Energy metabolism,DefinitionThe metabolic processes by which energy is made available for th

3、e use of the bodyThe main sources of chemical energy are carbohydrates, fats, and protein. The breakdown of organic molecules liberates the energy and ATP synthesis.The breakdown of ATP serves as the immediate energy source for biological work.Growth, repair, and physical activity.,ATP: “Energy Curr

4、ency”,ATP is generated by combustion of carbohydrates, fats and proteins.,Ribose,Adenine,Energy sources,Carbohydrates - mainly glucoseMajor source: 70 % of the total energyATP is producedBy glycolysis (oxygen independent )By citric acid cycle ( Krebs cycle requires oxidation )1g of glucose contains

5、4 kcal Glucose is stored as glycogen in the liver and the muscle,Energy sources,Fat fatty acidsMajor form of energy storage The storage of fat in the body is much greater than that of glucoseAlternative energy source 1g of fat contains 9 kcal,Energy sources,ProteinsThe amount of energy provided by p

6、roteins is relatively small in human being1g of protein contains 4 kcal Protein will become the major energy source to maintain the essential vital activities in special conditions,Cholesterol,A type of lipid does not serve as a metabolic energy source.A component of plasma membrane, bile salts, ste

7、roid hormones, etc.,Cholesterol,Triglyceride,Two states body provides energy,Absorptive state: ingested nutrients enter the blood from the gastrointestinal tract.Postabsorptive state: gastrointestinal tract is empty of nutrients and the bodys own stores must supply energy.,Metabolic pathways of the

8、absorptive state,Summary of metabolism during the absorptive state,1. Energy is provided primarily by absorbed carbohydrate in a typical meal.There is net uptake of glucose by the liver.Some carbohydrate is stored as glycogen in liver and muscle, but most carbohydrates and fats in excess of that use

9、d for energy are stored as fat in adipose tissue.There is synthesis of body protein, but some of the amino acids in dietary protein are used for energy or converted to fat.,Metabolic pathways of the postabsorptive state,Glucose sparing (fat utilization),Glycogenolysis (glucose generation by hydrolys

10、is of glycogen)Gluconeogenesis (glucose generation from non-carbohydrate carbon substrates, such as amino acids, glycerol and lactate.Glucose sparing: glycogenolysis and Gluconeogenesis cannot supply all the energy demands of the body. Other than the nervous system, most organs markedly reduce their

11、 glucose catabolism and increase their fat utilization. Fatty acids: plasma free fatty acids are taken up by almost all tissues and provide energyKetones: lipolysis in the liver produces ketones which are released to the blood and provide an energy source taken up by all tissues, include the nervous

12、 system.,Summary of metabolism during the postabsorptive state,Glycogen, fat and protein syntheses are curtailed and net breakdown occurs.Glucose is formed in the liver both from the glycogen and glyconeogenesis.The glucose produced in the liver is released into the blood, but its utilization for en

13、ergy is greatly reduced in nonneural tissues.Lipolysis releases adipose tissue fatty acids into the blood, and the oxidation of these fatty acids ketones provides most of the bodys energy supply.The brain uses glucose but also starts using ketones as they build up in the blood.,Endocrine control of

14、metabolism,Islets of Langerhans are clusters of endocrine cells in the pancreas.*Secrete two peptide hormones: cells: glucagon cells: insulin,Endocrine control of metabolism Insulin,Endocrine control of metabolism Insulin,Endocrine control of metabolism Glucagon,Stimulate gluconeogenesis, in particu

15、lar, in the liver.Mobilize amino acids from extrahepatic tissues.Inhibit glucose uptake in muscle and adipose tissue.Stimulate fat breakdown in adipose tissue.Net effects: Increased plasma concentration of amino acids, glucose and free fatty acids,Endocrine control of metabolism Cortisol,Energy expe

16、nditure,The metabolism of foodstuffs yields chemical energy and heat.Heat is the end product of almost all the energy released in the bodyAbout 60% of the energy released from organic molecules appears immediately as heat.The rest is used for work.,Basal metabolism,Basal metabolic rate (BMR)BMR in t

17、he basal conditionThe minimum energy expenditure for the body to exist50-70% of the daily energy expenditureBMR is usually expressed as calories per hour per square meter of body surface area,Method for determining BMR,To measure the rate of O2 utilization under the basal conditionsAt mental and phy

18、sical restRoom temperature: 20 to 25CKeep fasting for at least for 12 hours,Factors that influence the BMR,AgeSex: women less than men at any given age,Factors that influence the BMR,Thyroid hormone, male sex hormone, growth hormone and fever BMRSleep and malnutrition BMR,Thyroid hormone (T3 and T4)

19、,Required for normal maturation of the nervous system in the fetus and infants.Required for normal bodily growth.Required for normal alertness and reflexes.The single most important determinant of BMR.Facilitates the activity of the sympathetic nervous system,Factors that affect energy metabolic rat

20、e,Psychic activityEmotional stressMRSympathetic nerve activationE, NE,Factors that affect energy metabolic rate,Specific dynamic action of foods ( Diet induced thermogenesis)The ingestion of food rapidly increase the metabolic rate by 1020% for a few hours after eating.Most of the increased heat pro

21、duction is caused by the processing of the absorbed nutrients by the liver.Ingested protein produces the greatest effect.,Factors that affect energy metabolic rate,Environmental temperature,How to maintain a stable body weight,Energy balance is the difference between the number of kilocalories that

22、you eat (energy intake) and the number of kilocalories that you burn (energy expenditure),Energy intake,Appetitequality and quantity of foodculture influence,Energy expenditure,Energy expenditureAn effective meansphysical activity,Leptinsynthesized by adipose tissue cellsfunctions in a negative feed

23、back system to maintain a constant body weight StressGhrelinis released from endocrine cells in the fundus of stomach hunger gastric motility and acid productionburning of fat,Control of energy balance,Part 2 Body Temperature and Temperature Regulation,Body temperature,Skin temperatureChanging with

24、the temperature of the surroundings Core temperature Maintaining constant (when T=1254C),Normal core temperature,Physiological fluctuations of the body temperature,Circadian rhythmDiurnal rhythmic changes with a variation of 1 CThese rhythms originate in the hypothalamusCircamensal rhythmWomen have

25、a T rhythm that varies with the menstrual cycle.,Physiological fluctuations of the body temperature,AgeEmotional stressMuscle activityFood, drugs,Important to maintain a stable body temperature,Temperature regulation,Body temperature is controlled by balancing heat production against heat loss,Heat

26、production,Major organs of heat production in the body,Heat production,Modes of heat-productionShivering thermogenesisNon-shivering thermogenesisControl of thermogenesisThyroxine, catecholamines, androgens and GH Sympathetic nervous system,Shivering thermogenesis,Reflex change (shivering thermogenes

27、is)consists of rhythmic, oscillating skeletal muscle contractions primary controlled by hypothalamus,Nonshivering thermogenesis,occurs in brown adipose tissue (brown fat) that is present in human infants and hibernating mammalsis mediated by sympathetic stimulation and thyroid hormone,Heat loss,By t

28、he skinBy expiration, urination, and defecationBy panting,Heat is mainly lost from the skin,How is heat lost from the skin surface?,Radiation: 60%The emission of heat energy from the surface of a warm body in the form of electromagnetic waves, or heat waves (infrared heat rays)The human body both em

29、its and absorbs radiant energy,How is heat lost from the skin surface?,Conductionis the transfer of heat between objects of differing temperatures that are in direct contact with each otherThe rate of heat transfer by conduction depends on the temperature difference between the touching objects and

30、the thermal conductivity of the substances involved,Heat loss,Control of heat lossBy regulation of skin blood flowBy regulation of sweat glands,Regulation of body temperature,The temperature of the body is regulated almost entirely by nervous feedback mechanisms: hypothalamus:*It receives informatio

31、n from heat and cold thermoreceptors in the skin.*It also contains thermoreceptors which are sensitive to the temperature of the bodys blood.*The hypothalamus responds to this information by sending nerve impulses to effectors to return the body temperature back to normal.,Regulation of body tempera

32、ture,Temperature-regulating centersIn the hypothalamus,Temperature-decreasing mechanisms when the body is too hotVasodilatationSweatingDecrease in heat production,Temperature-increasing mechanisms when the body is too coldSkin vasoconstrictionIncrease in heat productionShivering Sympathetic excitationThyroxine (Eskimos-higher incidence of toxic thyroid goitres),The End.,