1、Catabolism and Anabolism nCatabolism:breaks down large molecules(such as polysaccharides,lipids,nucleic acids and proteins)into smaller units,releasing energy into smaller units(such as monosaccharides,fatty acids,nucleotides,and amino acids).nAnabolism:construct molecules from smaller units,requiri
2、ng energy.nAnabolism is powered by catabolism(hydrolysis of adenosine triphosphate(ATP).Part I Energy metabolism nDefinitionnThe metabolic processes by which energy is made available for the use of the bodynThe main sources of chemical energy are carbohydrates,fats,and protein.nThe breakdown of orga
3、nic molecules liberates the energy and ATP synthesis.nThe breakdown of ATP serves as the immediate energy source for biological work.nGrowth,repair,and physical activity.n ATP:“Energy Currency”ATP is generated by combustion of carbohydrates,fats and proteins.RiboseAdenineEnergy sourcesnCarbohydrates
4、-mainly glucosenMajor source:70%of the total energynATP is producednBy glycolysis(oxygen independent)nBy citric acid cycle(Krebs cycle requires oxidation)n1g of glucose contains 4 kcal nGlucose is stored as glycogen in the liver and the muscleEnergy sourcesnFat fatty acidsnMajor form of energy stora
5、ge The storage of fat in the body is much greater than that of glucosenAlternative energy source 1g of fat contains 9 kcal Energy sourcesnProteinsnThe amount of energy provided by proteins is relatively small in human beingn1g of protein contains 4 kcal nProtein will become the major energy source t
6、o maintain the essential vital activities in special conditionsCholesterolnA type of lipid does not serve as a metabolic energy source.nA component of plasma membrane,bile salts,steroid hormones,etc.CholesterolTriglycerideTwo states body provides energynAbsorptive state:ingested nutrients enter the
7、blood from the gastrointestinal tract.nPostabsorptive state:gastrointestinal tract is empty of nutrients and the bodys own stores must supply energy.Metabolic pathways of the absorptive stateSummary of metabolism during the absorptive staten1.Energy is provided primarily by absorbed carbohydrate in
8、a typical meal.nThere is net uptake of glucose by the liver.nSome carbohydrate is stored as glycogen in liver and muscle,but most carbohydrates and fats in excess of that used for energy are stored as fat in adipose tissue.nThere is synthesis of body protein,but some of the amino acids in dietary pr
9、otein are used for energy or converted to fat.Metabolic pathways of the postabsorptive stateGlucose sparing(fat utilization)nGlycogenolysis(glucose generation by hydrolysis of glycogen)nGluconeogenesis(glucose generation from non-carbohydrate carbon substrates,such as amino acids,glycerol and lactat
10、e.nGlucose sparing:glycogenolysis and Gluconeogenesis cannot supply all the energy demands of the body.Other than the nervous system,most organs markedly reduce their glucose catabolism and increase their fat utilization.nFatty acids:plasma free fatty acids are taken up by almost all tissues and pro
11、vide energynKetones: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 system.Summary of metabolism during the postabsorptive statenGlycogen,fat and protein syntheses are curtailed and net breakdown occurs.
12、nGlucose is formed in the liver both from the glycogen and glyconeogenesis.nThe glucose produced in the liver is released into the blood,but its utilization for energy is greatly reduced in nonneural tissues.nLipolysis releases adipose tissue fatty acids into the blood,and the oxidation of these fat
13、ty acids ketones provides most of the bodys energy supply.nThe brain uses glucose but also starts using ketones as they build up in the blood.Endocrine control of metabolismnIslets of Langerhans are clusters of endocrine cells in the pancreas.*Secrete two peptide hormones:cells:glucagon cells:insuli
14、nEndocrine control of metabolism InsulinEndocrine control of metabolism InsulinEndocrine control of metabolism GlucagonnStimulate gluconeogenesis,in particular,in the liver.nMobilize amino acids from extrahepatic tissues.nInhibit glucose uptake in muscle and adipose tissue.nStimulate fat breakdown i
15、n adipose tissue.Net effects:Increased plasma concentration of amino acids,glucose and free fatty acidsEndocrine control of metabolism CortisolEnergy expenditurenThe metabolism of foodstuffs yields chemical energy and heat.nHeat is the end product of almost all the energy released in the bodynAbout
16、60%of the energy released from organic molecules appears immediately as heat.nThe rest is used for work.Basal metabolismnBasal metabolic rate(BMR)nBMR in the basal conditionnThe minimum energy expenditure for the body to existn50-70%of the daily energy expenditurenBMR is usually expressed as calorie
17、s per hour per square meter of body surface area Method for determining BMR nTo measure the rate of O2 utilization under the basal conditionsnAt mental and physical restnRoom temperature:20 to 25CnKeep fasting for at least for 12 hours Factors that influence the BMRnAgenSex:women less than men at an
18、y given ageFactors that influence the BMRnThyroid hormone,male sex hormone,growth hormone and fever BMRnSleep and malnutrition BMRThyroid hormone(T3 and T4)nRequired for normal maturation of the nervous system in the fetus and infants.nRequired for normal bodily growth.nRequired for normal alertness
19、 and reflexes.nThe single most important determinant of BMR.nFacilitates the activity of the sympathetic nervous systemFactors that affect energy metabolic ratenPsychic activitynEmotional stressMRnSympathetic nerve activationnE,NEFactors that affect energy metabolic raten Specific dynamic action of
20、foods(Diet induced thermogenesis)nThe ingestion of food rapidly increase the metabolic rate by 1020%for a few hours after eating.nMost of the increased heat production is caused by the processing of the absorbed nutrients by the liver.nIngested protein produces the greatest effect.Factors that affec
21、t energy metabolic ratenEnvironmental temperatureHow to maintain a stable body weightnEnergy balance is the difference between the number of kilocalories that you eat(energy intake)and the number of kilocalories that you burn(energy expenditure)Energy intakenAppetitenquality and quantity of foodncul
22、ture influenceEnergy expendituren Energy expenditurenAn effective meansnphysical activitynLeptinnsynthesized by adipose tissue cellsnfunctions in a negative feedback system to maintain a constant body weight nStressnGhrelinnis released from endocrine cells in the fundus of stomach n hungern gastric
23、motility and acid productionnburning of fatControl of energy balancePart 2 Body Temperature and Temperature Regulation Body temperature nSkin temperaturenChanging with the temperature of the surroundings nCore temperature nMaintaining constant(when T=1254C)Normal core temperatureSiteMean value of te
24、mperatureStandard deviationRange of variation of temperatureAxilla36.79oC0.35736.0-37.4 oCOral cavity37.19 oC0.24936.7-37.7 oCRectum37.47 oC0.25136.9-37.9 oCPhysiological fluctuations of the body temperaturenCircadian rhythmnDiurnal rhythmic changes with a variation of 1 CnThese rhythms originate in
25、 the hypothalamusnCircamensal rhythmnWomen have a T rhythm that varies with the menstrual cycle.Physiological fluctuations of the body temperaturenAgenEmotional stressnMuscle activitynFood,drugsnImportant to maintain a stable body temperatureCore Temperature()Symptoms28muscle failure30loss of body t
26、emperature control 33loss of consciousness37normal42central nervous system breakdown44 deathTemperature regulationnBody temperature is controlled by balancing heat production against heat loss Heat productionnMajor organs of heat production in the bodyPercentage inbody weightPercentage in At resthea
27、t-production During laborThe brain2.5161The internalorgans(i.e.liver and spleen,etc.)34568The muscle&skin561890The Others7.5101Heat productionnModes of heat-productionnShivering thermogenesisnNon-shivering thermogenesisnControl of thermogenesisnThyroxine,catecholamines,androgens and GH nSympathetic
28、nervous systemShivering thermogenesisnReflex change(shivering thermogenesis)nconsists of rhythmic,oscillating skeletal muscle contractions nprimary controlled by hypothalamusNonshivering thermogenesisnoccurs in brown adipose tissue(brown fat)that is present in human infants and hibernating mammalsni
29、s mediated by sympathetic stimulation and thyroid hormoneHeat lossnBy the skinnBy expiration,urination,and defecationnBy pantingHeat is mainly lost from the skinHow is heat lost from the skin surface?nRadiation:60%nThe emission of heat energy from the surface of a warm body in the form of electromag
30、netic waves,or heat waves(infrared heat rays)nThe human body both emits and absorbs radiant energy How is heat lost from the skin surface?nConductionnis the transfer of heat between objects of differing temperatures that are in direct contact with each othernThe rate of heat transfer by conduction d
31、epends on the temperature difference between the touching objects and the thermal conductivity of the substances involved Heat lossnControl of heat lossnBy regulation of skin blood flownBy regulation of sweat glandsRegulation of body temperaturenThe temperature of the body is regulated almost entire
32、ly by nervous feedback mechanisms:hypothalamus:*It receives information 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
33、return the body temperature back to normal.Regulation of body temperaturenTemperature-regulating centersnIn the hypothalamusnTemperature-decreasing mechanisms when the body is too hotnVasodilatationnSweatingnDecrease in heat productionnTemperature-increasing mechanisms when the body is too coldnSkin vasoconstrictionnIncrease in heat productionnShivering nSympathetic excitationnThyroxine(Eskimos-higher incidence of toxic thyroid goitres)The End.
