energy metabolism & body temperature · 2017-12-20 · body temperature regulation . body...
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Ying-ying Chen, PhDDept. of Physiology, Zhejiang University School of Medicine
bchenyy@zju.edu.cn
HUMAN PHYSIOLOGYHUMAN PHYSIOLOGYChapter 16Chapter 16
Energy Metabolism &Body Temperature
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SECTION A ENERGY METABOLISM
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Energy BalanceThe difference between the number of kilocalories that you eat and the number of kilocalories that you burn
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Energy intakeEnergy sources
Fat -> fatty acids Long carbohydrates -> shorter -> glucose Shorter carbohydrates ('sugars') -> glucose Proteins -> Amino acids
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Glucose: a major energy sourceAerobic oxidation
Glycolysis
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Fat
Major form of energy storage
Alternative Energy Source
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Proteins
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Energy transferATP: primary energy currency
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Phosphocreatine: an ATP “buffer”
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Energy expenditure
Heat is the end product of almost all the energy released in the body
heat heat
heat
50%20%
25%
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Metabolic rate
Normally expressed in terms of the rate
of heat liberation during the chemical
reactions
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Factors that affect metabolic rate
Physical Activities
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Thermogenic effect of food-Specific Dynamic Action of protein
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Psychic activity
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Environmental temperature
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Basal metabolic rate (BMR)The minimum energy expenditure for the body to exist
0102030405060708090
100
% D
aily
ene
rgy
expe
rndi
ture
Basal metabolism
(60%)
Physical activity(25%)
Thermic effect of food (8%)
Nonexercise activity (7%)
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Determining BMR under the following conditions
Keep fast at least for 12 hours After a night of restful sleep
No strenuous activityEliminated psychic and physical factors RT: 16 to 27°CNo physical activity during the test
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BMR is usually expressed as Calories per hour per square meter of body surface area
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Other Factors that influence the BMR
Thyroid hormone, male sex
hormone, growth hormone
Fever
Sleep
Malnutrition
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SECTION B
BODY TEMPERATURE REGULATION
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Body temperature
Core temperature Homeostatically maintained at 37℃
Skin temperatureinfluenced by the environment
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Normal body temperature
36.9-37.9℃Rectum
36.7-37.7℃Oral cavity
36.0-37.4℃Armpit
Range of Variation of TemperatureSite
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Important to maintain a stable body temperature
death44 central nervous system breakdown42normal37loss of consciousness33loss of body temperature control 30muscle failure28
SymptomsCore Temperature (℃)
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Factors affecting normal body temperature
Circadian rhythmoriginates in the hypothalamus
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Sex
7 14 21 2836.0
36.2
36.4
36.6
36.8
37.0
37.2
37.4
day
Tem
pera
ture
(o C)
Ovulation is marked by a rise in temperature
0.5℃
menstruation
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AgeMuscle activity
40
37
Tem
pera
ture
(oC
)
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Other factors
Emotion
Eating
Environment temperature
Vascular activities
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Heat production
A principal by-product of the metabolismBasal metabolismExtra metabolism caused by
Muscular activityHormones (thyroxine)Sympathetic nervous systemDietary intake
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Main organs of heat production in the body
heat production (%)
1107.5Others901856Skeletal muscle
85634viscera (especially liver)
1162.5Brainworkingat rest
Percentage in Body Weight
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Muscle activity Reflex change (shivering thermogenesis)
Primary controlled by hypothalamus
rhythmic, oscillating skeletal muscle contractions
Voluntary change
Cold exposure
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Chemical activity (non-shivering thermogenesis)
Brown adipose tissue
Electron transport chain
H+
H+ H+
Uncoupling protein
ATP synthase
heat
ATPADPNADH
GlucoseFatty acids
Mitochondrial matrix
cytosol
Intermembrane space
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Mediated by sympathetic stimulation and thyroid hormone
Observed in the following natural situations
In small children
In cold adaptation
In hibernating animals
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Heat LossHeat transfer
Deep organs Skin Air and other surrounding
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heat transfer from the body core to skin
flow of bloodcontrolled by the sympathetic nervous system
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Heat is lost from the skin
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Radiationin the form of electromagnetic waves
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ConductionTemperature difference between the touching objectsThermal conductivity
heating pad
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ConvectionAir (H2O) currents
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Evaporation
Required to transform water from a
liquid to a gaseous state
Forms
Insensible Evaporation
Evaporation of sweat
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Sweating An active evaporative heat loss process
Sweat gland
Cholinergic sympathetic nerve innervation
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Body temperature is controlled by
balancing heat production against heat loss
Temperature Regulation
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Thermoregulatory centerPreoptic/anterior hypothalamus (PO/AH)
Thermostat: set point
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set point theory
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FeverPyrogens: Shift the set point
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Temperature receptors
PO/AHHeat-sensitive neurons
Cold–sensitive neurons
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Skin temperature receptors Cold receptors
Warmth receptors
Deep body temperature receptors Spinal cord, abdominal viscera, great veins
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PO/AH monitors its own temperature and receives input from receptors in skin & spinal cordBehavioral control of temperature
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Cold exposure
Immediate reflex effects
Shivering
Nonshivering thermogenesis (Sympathetic excitation)
Skin vasoconstriction
Chronic effect
Thyroxine
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Vasodilatation
Sweating
Decrease in heat production
when the body is too hot
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Summary
TermsSpecific dynamic action of proteinBasal metabolic rateBody temperatureSet-point
List the factors that affect energy metabolic rateDescribe the modes of heat-loss from the skin