Energy Balance and Temperature Regulation

Definition of energy metabolism liberation storage transformation utilization liberation 2

Energy balance energy input =energy output

Energy Balance The difference between the number of kilocalories that you eat and the number of kilocalories that you burn obesity

Food energy Metabolic pool in body External work Internal work Thermal energy (heat) Energy storage Energy input Energy output First law of thermodynamics: Energy cannot be created or destroyed, but it can be converted from one form to another

Source and utilization of energy Foods (carbohydrate,fat and protein) Heat (>50%) O2 ATP Muscle contraction Nerve conduction Active transport Digestion Secretion Anabolism C oxidation C-P Energy <50% ADP Pi H2O,CO2 release transport storage utilization

ATP ATP is a combination of adenine,ribose,and three phosphate radicals. adenine 7

ATP(adenosine triphosphate) ATP:An energy “currency” ATP is generated by combustion of carbohydrate, fat and protein . ATP can be utilized by cell directly (high energy phosphate bonds) Synthesis and growth Muscular contraction Nerve conduction Active transport Gland secretion

Phosphocreatine Phosphocreatine: Another energy-rich phosphate compounds found in the muscle and brain acts as an accessory depot for energy of ATP and for buffering the concentration of ATP

This reversible interrelation between ATP and phosphocreatine is demonstrated by the following equation: Phosphocreatine+ADP=ATP+Creatine

Energy expenditure

energy input (food) Carbohydrate (mainly glucose ) 65% of the total energy (4.1kcal/g ) Glycolysis Citric acid cycle

Glucose: a major energy source Oxidation 6

energy input (food) Fat – fat acid (9.5kcal/g) The storage fat in the body is much greater than that of glucose The energy released by oxidation of fat is 2 times that produced by the same amount of glucose

energy input (food) Protein: (synthesize body structure protein) 4.3kcal/g The amount of energy provided by protein is relatively small in human being In special situation , the protein is the main source of energy . (Hungry for a long time)

Factors control food intake

The feeding center tell us to eat, whereas the satiety center tell us when we have had enough.

comparison of a normal rat with a rat whose satiety center has been destroyed.

Factors control food intake The size of fat stores Leptin:excellent indicator of total amount of TG store Leptin↑+ receptor →appetite↓and metabolic rate↑ Recepter:in the ventromedial hypothalamus(satiety center) Suppression of appetite Responsible for the long-term matching of food intake to energy expenditure

Factors control food intake The extent of glucose utilization and insulin secretion insulin→signals satiety The extent of glucose utilization appears to be more important in determining the timing of meals Low blood glucose levels activate lateral hypothalamic neurons in the vicinity of appetite centers

Factors control food intake Psychosocial and environmental influences Stress, anxiety, depression and boredom →unrelated to energy needs Food supplies are abundant

Energy 0utput Internal work External work: Na＋- K＋pump muscle contraction (shivering) or maintain the posture External work: go upstairs (potential energy ↑ ) lift the object from low site to high one

Energy 0utput Form of energy output Heat (During biochemical processing) 75% of the energy is lost as heat (directly) 25% of the energy is available to accomplish work (internal work or external work) (indirectly) Energy in Nutrient molecules 50% ATP 25% lost as heat during expenditure 25% energy accomplish work 75% energy will be lost as heat 50%heat

Obesity 20%overweight greater than normal body mass index(BMI)=height2/weight BMI≥24: overweight BMI≥28: obesity

Obesity 20%overweight greater than normal Energy intake ＞energy expenditure Abnormal feeding regulation Psychogenic factor During or after stressful situation Neurogenic abnomality Hypothalamas Disturbances of the satiety-appetite control Genetic factor Childhood overnutrition

Three possible states of energy balance Neutral energy balance : Energy input =energy expended Positive energy balance : Energy input > energy expended, store in adipose tissue , body weight increase– obesity Negative energy balance : Energy input < energy expended, lose weight

Energy Metabolism

Terminology metabolic rate = energy expenditure/unit of time (kcal/hr) Heat is the end product of almost all the energy release in the body Calorie : the basic unit of heat energy --the amount of heat required to raise the temperature of 1g of H2O 1℃

Method of metabolic rate determination

Direct calorimetry If person doesn’t do external work, energy output = heat released, we calculate the heat liberated from the body in a given time by a special calorimeter. so we can determinate the metabolic rate.

Measurement of metabolism rate Direct calorimetry water thermometer thermometer Thick insulation water

Measurement of metabolism rate Indirect calorimetry Principle: food + O2→CO2+H2O+energy(heat) C6H12O6+6O2 → 6CO2+6H2O + H (law of definite proportions )

Measurement of metabolism rate Indirect calorimetry Energy (Thermal) equivalent of food Heat production (The amount of energy liberated ) by oxidation or combustion of 1g of such food physical caloric value and biological caloric value Energy equivalent of oxygen Heat production (The amount of energy liberated ) by consuming of one liter of oxygen to oxidize a specific type of food glucose: 5.01 kcal, fat: 4.7 kcal, protein: 4.6 kcal

typical mixed diet is 4.8 Kcal

metabolic rate = energy expenditure/unit of time Indirect calorimetry An average estimate of the quantity of heat produced per liter of O2 consumed on a typical mixed diet (Energy equivalent of oxygen ) 15 liter/hr =O2 consumption ×4.8 Kcal/liter =energy equivalent of O2 72 Kcal/hr =estimated metabolic rate ? metabolic rate = energy expenditure/unit of time

Indirect calorimetry Method of measuring O2 consumption Closed circuit method

law of definite proportions C6H12O6+6O2 6CO2+6H2O + H Heat = thermal equivalent of oxygen ×the amount of O2 consumed Metabolic rate = Thermal equivalent of oxygen (4.825kcal/L)×oxygen utilized(L).

Counterbalancing weight water Recording drum Soda lime Mouth piece Counterbalancing weight volume time

Factors affect the energy metabolic rate Physical activity

Factors affect the energy metabolic rate Psychic activity stress elicits 他和secretion of the hormone epinephrine,chich increases the metabolic rate

Factors affect the energy metabolic rate Thermogenic effect of food Specific dynamic action of food the metabolic rate of a person increases after a meal. Protein increase it significantly.

Factors affect the energy metabolic rate Environment temperature: >30℃ or <20 ℃ metabolic rate↑

Rate of energy expenditure for a 70kg person during different types of activity Form of activity energy expenditure (Kcal/h) Sleeping 65 Sitting at rest 100 Typewriting 140 Walking slowly on level 200 Bicycling on level 304 Swimming 500 Jogging 570 Rowing 828 Walking up stairs 1100

Basal metabolic rate (BMR)

BMR The minimum energy expenditure for the body to existence the heat output in kilocalories per hour per square meter of surface area is normally about the same.

BMR is not the lowest metabolic rate, metabolic rate will reduce further in deep sleep

Basal metabolic rate (BMR) minimal waking rate of internal energy expenditure under basal condition basal condition physical rest: muscle and nerve relaxation room temperature: 20-25 ℃ Fasting: Not have any eaten food 12 hours before determination waking?

Why should subject keep awake?

Method for determining BMR Under the following condition At physical rest At mental rest At a comfortable room temperature Avoiding Specific dynamic action of food

The meaning of determining the BMR For a healthy person, the BMR does not vary more than 10 to 15 percentage from the normal values. Hyperthyroid: increase 25%~80% Hypothyroid: decease 20%~25%

Other factors affected the BMR Gender and age

Other factors affected the BMR Hormone Thyroid hormone : BMR↑ Male sex hormone Sleep and malnutrition Deep sleep : BMR↓ ↓ BMR is not the lowest metabolic rate, metabolic rate will reduce further in deep sleep

how to compare MR of different person?

Because sex age height and weight affect the basal rate of energy expenditure. the output in kilocalories per hour per square meter of surface area is normally about the same. The BMR is usually expressed as calories per hour per square meter of body surface area

Data used to measure energy Thermal( Energy) equivalent of food The amount of energy liberated by oxidation or combustion of 1g of such food thermal ( Energy) equivalent of oxygen Heat production by consuming of one liter of oxygen to oxidize a specific type of food the amount of the food oxidation the amount of the O2 consumption

Temperature regulation

Why keep the temperature constantly？

Even moderate elevations of body temperature begin to cause nerve malfunction and irreversible protein denaturation. Higher than 44 to 45℃, maintained for certain length of time is also fatal. An optimum environment for the cells, it is necessary to maintain a constant body temperature.

Body temperature Skin temperature : Core temperature: variation by surrounding temperature Core temperature: maintaining constant the body may conveniently be viewed as a central core surrounded by an outer shell.

Normal core temperature No single temperature level can be considered to be normal, it is a range

Influence factors of core temperature

Physiological fluctuation of the body temperature Influence factors of core temperature Circadian rhythm Diurnal rhythmical changes with a variation of 1℃ biological clock circadian美 [sɝ'kedɪən] biological clock

Influence factors of core temperature Sex different in body temperate Female : check safe period 0.5 ℃ higher during the half of the cycle from the time of ovulation to menstruation

Influence factors of core temperature : the older , the lower

Influence factors of core temperature Emotional stress: Food :specific dynamic action of food Drugs: tranquilizer

Temperature regulation Heat gain must balance heat loss to maintain a stable temperature

Temperature regulation Heat production Major organs of heat production in the body

Temperature regulation Modes of heat production Shivering thermo-genesis: rhythmic oscillation skeletal muscle contractions Non - shivering thermo-genesis brown fat : a special fat tissue in newborn Mediated by hormone: Thyroid hormone and epinephrine Important for newborns (lack the ability to shiver)

Temperature regulation Heat loss (down temperature gradient) By skin By expiration, urination and defecation By panting

Temperature regulation How heat is lost from the skin surface? (down a thermal gradient) Radiation (60%) :by Infrared heat rays emission or absorption depend on the difference in temperature between the surface of skin and other object in the environment camouflage clothes camouflage clothes 迷彩服

Temperature regulation How heat is lost from the skin surface? Conduction : in direct contact with each other Conduction to solid subjects Conduction to air Effect of clothing on conductive heat loss

Temperature regulation How heat is lost from the skin surface? Convection (air or water current) Cooling effect of wind

Conduction and convection Similarity: direct heat transfer to the material which contacts with the body Dissimilarity conduction :Heat transfer to and from solids Convection: heat is transferred from the skin by conduction to the air heated air moves away from the skin, more heat is lost to the unheated air that is continually brought in contact with the skin

Temperature regulation How heat is lost from the skin surface? When T Environmental ＞ T skin ,evaporation is the only avenue for heat loss body is gaining heat by radiation and conduction 0.58 Calorie of heat is lost for 1g water that evaporates

Temperature regulation How heat is lost from the skin surface? Evaporation (T Environmental ＞ T skin ) Insensible evaporation : airways and surface of skin (without controlled , passive) 450ml – 600ml H2O/day (fluid infusion) Sensible evaporation: sweat (hot , humid days) Sweat gland: sympathetic cholinergic nerve innervations Evaporating and dripping of sweat

Regulation of body temperature temperature-regulating centers: hypothalamus Afferent input Peripheral thermoreceptors: Skin cold and warmth receptor more cold receptors than warmth receptors Central thermoreceptors : hypothalamus itself

Temperature regulation (Control of heat loss) Posterior region of hypothalamus activated by cold triggers reflexes :mediate heat production and heat conservation. skin vasoconstriction Increase in heat production Anterior region of hypothalamus, activated by warmth initiates reflexes :mediate heat loss Vasodilation sweating Decrease in heat production

Temperature regulation Nervous feedback mechanism (short term) Humeral regulation : thyroid gland hormone( long term ) Behavioral control : shivering

Temperature regulation Hypothalamus : sensitive thermostat The concept of set point: thermostat Any deviation from a very critical body core temperature, between the level of 37.0 and 37.1℃, would cause drastic change in both the rate of heat loss and heat production, then bring the body temperature back to set point

T skin T core Peripheral thermo receptors (skin) Central thermo receptors (in hypothalamus) Hypothalamus thermoregulatory center Behavioral adaptations Sympathetic nervous system Motor neurons sweating Muscle tone Skin vaso -constriction and vasodilation Control of heat production or loss Major thermoregulatory pathway

Abnormality temperature regulation Fever : the point is reset at an elevated temperature. endogenous pyrogen: raise the “set-point” .(PG↑) (Aspirin )

Hyperthermia : no related to infection --malfunction of the hypothalamic control centers Hyperthermia in sustained exercise: heat loss mechanism reflexly increased

Abnormality temperature regulation Heat stroke Breakdown of the hypothalamic thermoregulatory systems Prolonged exposure to a hot humid environment

Abnormality temperature regulation Frostbite Excessive cooling of a particular part of the body , the tissue in that area is damaged

Summary Definition List the factors that affect energy metabolic rate 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

Question How does the body actively maintain a constant body temperature despite changes in ambient temperature?