Energy Balance and Temperature Regulation Energy Balance Temperature Regulation
Jan 12, 2016
Energy Balance and Temperature Regulation
Energy Balance
Temperature Regulation
Definition of energy metabolism
Energy metabolism liberation storage transformation utilization
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)
H2O,CO2
O2
oxid
atio
n
ATP
ADP
Pi
C
C-P
Heat
(>50%)
Energy
<50%
Muscle contraction
Nerve conduction
Active transport
Digestion
Secretion
Anabolism
release transport storage utilization
ATP
ATP is a combination of adenine,ribose,and three phosphate radicals.
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
Oxidation6
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 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)
50%heat
Energy in
Nutrient molecule
s
50% ATP
25% lost as heat during
expenditure
25% energy accomplish work
75% energy will be lost as
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
thermometer
thermometer
water
water
Thick insulation
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
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
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).
law of definite proportions
Mouth piece
Soda lime
waterRecording drum
Counterbalancing weight
volume
time
Factors affect the energy metabolic rate
Physical activity
Psychic activity
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
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 65Sitting at rest 100Typewriting 140Walking slowly on level 200Bicycling on level 304Swimming 500 Jogging 570 Rowing 828 Walking up stairs 1100
Basal metabolic rate (BMR)
BMR
The minimum energy expenditure for the body to existence
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 : variation by surrounding temperature
Core temperature: maintaining constant
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
Circadian rhythm Diurnal rhythmical changes with a variation of 1℃
Influence factors of core temperature
biological clock
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
Influence factors of core temperature
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
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
Motor neurons Sympathetic nervous system
Control of heat production or
loss
Muscle tone Skin vaso -constriction and
vasodilation
sweating
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 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?