Metabolism

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Metabolism Regulation of Body Temperature
By Dr. Khaled Ezam Physiology Department
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OBJECTIVES

• 1-Understand the basis of energy balance.
• 2-Define BMR and its significance.
• 3-Respiratory Quotient.
• 4-Understand the basis of thermal balance.
• 5-Explain the thermoregulatory response to cold
  and hot atmosphere.

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Physiology of Energy Metabolism

• Metabolism
• Anabolism
• Glucose Energy---------Glycogen
• Catabolism
• Glycogen----------Glucose ENERGY
• Energy in the form of ATP
• ATP combustion of food stuffs ,carbohydrates,
  lipids, proteins.
• Degradation of ATP ? 24 kcal/molecule.

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ATP

• Synthesis of most intracellular components.
• Synthesis of glucose.
• Synthesis of fatty acids.
• Synthesis cholesterol,phospholipids, hormones,
• Synthesis of urea.
• Source of muscle energy.
• Energizes active transport across membranes.
• Energizes glandular secretion.
• Energizes nerve conduction.

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ENERGY BALANCE
Energy intake Energy output
If energy intake more than energy output
------------ obesity state.
If energy intake less than energy output
------------- thin state.
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Origin of Energy Input
Food intake.
Stored glycogen triglycerides.
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Energy output

• 60---------BMR.
• 8----------Thermic effect of food
• cold induced thermogenesis.
• 7----------Spontaneous purposeless activity.
• 25---------Purposeful physical activity.

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Unit of Energy

• Kilocalorie(Kcal) the amount of heat required to
  raise the temperature of one Kg. of water from
  15-16 C.
• ( kcal capital C)
• Kilocalorie 1000 calorie.
• Physical heat value the amount of energy
  liberated when 1 gm. of substrate is completely
  oxidized outside the body
• Caloric value of food ( physical heat value)
• CHO ------------4.1 C/gm
• Fats--------------9.3 C/gm
• Protein-----------5.6 C/gm

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Physiological heat value

• The amount of energy liberated by 1 gm. of food
  substrate when they are completely oxidized
  inside the body.
• CHO--------------------4.0 C/gm.
• Fats----------------------9.0 C/gm.
• Protein------------------4.1 C/gm.
• physiological heat value of protein (4.1)
  less than physical heat value( 5.6) due to
  incomplete oxidation of protein as complete
  oxidation lead to formation of nitric acid which
  is fatal.
• The difference between physical and
  physiological values are due to variations in GIT
  absorption, 98 CHO, 95 fats and 92 protein

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Caloric value of oxygen heat value

• Is the amount of heat generated when 1 liter of
  oxygen used to oxidize different food stuffs.
• CHO produces 5 C.(kcal)
• Fat produces 4.7 C.(kcal)
• protein produces 4.5 C.( kcal)
• Mixed food produces 4.8 C. (kcal)

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Respiratory Quotient (RQ)

• CO2 production
• RQ --------------------- as a ratio
• O2 consumption.
• At rest
• O2 consumption250-300 ml/min(VO2).
• CO2 production 200-250ml/min(VCO2).

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Importance of RQ

• Determines the nature of food substance oxidized
  in different tissues and under
• different conditions.
• CHO ------------RQ1.
• Fat---------------RQ0.7.
• Protein-----------RQ0.8.
• Transformation of one food substance into another
  one.
• CHO(O2 rich) ----------------Fat
  (O2-poor)----------------------more CO2
  production so higher RQ.
• 3. Determines the caloric value of O2 using
  special metabolic tables.
• 4. Denotes the type of food utilization after
  their absorption
• If RQ1 ----------CHO utilization.
• If RQ0.7---------Fat utilization.
• 5. Negative RQ( arterial CO2 gt venous CO2 ) as
  in
• - HCL secretion in stomach.
• - HCO3 secretion in pancreas
• - Formation of intraocular formation.
• - Utilization of CO2 by the kidney to get
  red of H.

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Basal Metabolic Rate

• The absolute minimal energy expenditure of the
  body to exist under basal conditions.
• Criteria of basal conditions
• at the morning.
• 12-14 after the last meal.
• Complete physical and mental rest.
• Resting and supine position.
• Comfortable temperature 20-25C.
• Normal body temperature.

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Importance of BMR

• 1. Generating maintaining ionic gradients and
  other molecules across membranes.
• 2. The mechanical work of respiration.
• 3. Circulation of blood.
• 4. Production of muscle tone, signals
  conduction in nervous system.
• 5. Obligate heat loss via body surfaces to the
  environment.

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Factors affecting BMR

• Physiological factors
• Age
• Newborn 25C/H/M2
• Age2-5 years60C/H/M2
• Age 20 years40C/H/M2
• Above 20 years ? Decreased 1C/10 years.
• Sex
• BMR is lower in female by about 7
• due to more fat store with little metabolic
  activity.

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• Normal value of BMR
• In adult man 40 C/H/M2 15 .
• Clinical expression of BNR
• Expressed as a of increase or decrease from
• the normal standard value for the subject.
• e.g. If BMR 60 C/H/M2( 20 C/H/M2)
• Exceeding the normal standard value by
  20
• so, 50 ( higher than normal value
  i.e.
• 15 for his age and sex)

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• Race
• pure race as Chinese have
• lower BMR.
• Mixed race as Egyptians have
• higher BMR.
• Dark races have higher BMR
• than white races.
• Climate
• BMR is higher 10 in cold zone
• than in hot zone.

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• Physical habits
• Athletes have BMR about 10
• higher than in sedentary due to
• more muscle bulk and lesser
• amount of fat stores.
• Dietetic habit
• prolonged ingestion of protein
• increases BMR 10 more than
• eating CHO. or mixed diet.

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• Pregnancy
• pregnant women have higher
• BMR than non pregnant due to
• additional metabolism of fetus.
• Anxiety stress
• Higher BMR due to increase
• the level of stress hormone
• adrenaline, noradrenaline,
• cortisone.

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• Sleep
• Lower BMR by 10-15 due to
• - Decreased skeletal muscle
• tone.
• - Decreased activity of SNS.
• 2. Pathological factors
• Higher BMR,
• . Hyperthyroidism up to 100
• . Hyperpituitarism due to
• - G.H. - TSH

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• . Hyperadrenalism due to more
• secretion of catecholamines.
• . Hyperpyrexia Higher BMR by
• 10-14 for each 1C rise in body
• temperature.
• . Heart failure Higher BMR due to
• increase activity of respiratory
• muscles.
• . Diabetes insipidus Higher BMR
• to maintain body temperature.

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• Lower BMR
• Hypothyroidism
• Hypopituitrism
• Hypofunction of adrenal cortex.
• Hypothermia Decreased BMR
• 10 for each 1C lower.
• Prolonged starvation,
• - Depression of SNS.
• - Decreased catecholamines.
• - Decreased thyroxine and
• corticoids.

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• 3. Chemical factors
• Hormones,
• Thyroid h. most stimulant.
• TSH Adrenaline
• ACTH cortisone.
• G.H. increase BMR 15-20
• due to direct stimulation of
• cellular metabolism.
• Male sex h. increase BMR
• 10-15.

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• Drugs
• Caffeine
• - Central stimulant action.
• - Increase CAMP.
• Antithyroid agents
• - block production of thyroid h.
• Alcohol
• - Increase heat loss due to
• cutaneous V.D. so ? BMR to
• maintain body temperature.

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Body Temperature

• The body temperature of human body is maintained
  within 0.6 C of its normal value 37.0 C(98 F)
  .
• Constant body temperature is essential for
  optimum enzymatic activity.
• Homeostasis depends upon the balance between heat
  gain heat output.

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Variations in body temperature

• Diurnal Rhythm
• ? in the morning?? in the early afternoon??
  in the midafternoon
• ( maximum activity).
• Children have higher temperature .
• Adult women show body temperature changes related
  to menstrual cycle.

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• 4. Prolonged inactivity exposure to cold
  environment ??body temperature.
• 5. Emotional stress, muscular exercise, activity,
  and exposure to hot environment
• ?? body temperature.
• 6. Febrile illness state of thyroid gland
  affect body temperature.

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Measurements of body temperature

• Core temperature.
• Site Deep organs
• ----- almost keep constant.
• ----- Oral, Rectal,Axillary routes.
• ----- Oral lt Rectal by o.5C
• ----- Axillary lt Rectal by 1C
• ----- Rectal is the most accurate route.
• ----- Ranges between ( morning oral ) 36.5
  37.2C at room temperature 24 -25C.

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• 2. Skin temperature
• ----- Surface temperature.
• ----- Fluctuates with ambient temperature.
• ----- Highest in areas of head , chest ,and
  abdomen 34C, big muscles 30C and small
  muscles,28C.

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(No Transcript)
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Heat gain

• Heat production
• . BMR.
• . Exercise.
• . Specific dynamic action (SDA).
• . Extra- metabolism by
• Thyroxine.
• Growth hormone testosterone.
• Sympathetic nervous system.
• Cell activity.
• Heat uptake
• . Ambient temperature gt Skin temperature.

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Heat Loss

1. Most of heat loss is produced by deep organs
   especially liver, brain ,heart and skeletal
   muscles.
2. Conveyed to the surface through the tissues to
   the skin only if the skin temperature is lt core
   temperature.

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• Rate of heat Loss depends upon
• Rate of heat production by the body tissues.
  
• 2. Rate of heat conduction from deep organs to
  skin.
• 3. Rate of heat transfer from the skin to the
  surroundings.
• Skin blood supply( cutaneous blood supply).

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• Source of heat production
• In 70-kg normal person, Energy requirements
  
• At rest 75 80 Kcal / hour.
• During exercise 1400 Kcal/ hour.
• Behavioral responses,
• - in cold weather ---- increased food intake.
• - in hot weather ---- decreased food intake.

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• 2. Physiological responses,
• a) Muscle tone
• - increased gradually by signals from
  hypothalamus, ? MR up to 50 100 .
• b) Shivering
• - It is involuntary response to a fall in
  core body temperature.
• - It can be stopped or reduced by voluntary
  pathways.
• - It is characterized by , not rhythmic ,
  no actual muscle shaking, gradually increase in
  MT above a certain level leads to shivering
  begins( asynchronous contraction and relaxation
  of small antagonistic muscle groups a rate of
  about 10 20 / second.
• - It is controlled via hypothalamic
  signals.
• - Most of energy is transformed into heat,
  since no external work is done.
• - It can be abolished by ,alcohol,crure.
• - It can be induced by ingestion of cold
  food.

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• 3. Endocrinal responses( chemical thermogenesis)
  
• a) Catecholamines SNS excitation.
• -?MR by uncoupling phosphorylation
• - ?FFA release of fat stores
• - VC of skin blood vessels?? heat loss
• - Stimulate glycogenolysis in liver
• b) Thyroid hormone.
• - Long exposure to cold stimulate
• thyroid hormone secretion ??MR by
• uncoupling phosphorylation.

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• c) Hypothalamic hormone.
• - TSH.
• - ACTH Glucocorticoids.
• - ADH.
• d) Effect of clothing.
• - Protect the body against heat loss.
• - Clothes act as air traps which is a bad
  
  conductor of heat.

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2- Rate of heat conduction from deep organs to
the skin

• Blood flow to the skin from the body core
  provides heat transfer. Blood vessels are
  distributed profusely in SC tissues. The rate of
  cutaneous blood flow into skin venous plexuses
  vary 0 30 of cardiac output according to the
  surrounding temperature and the state of CVS
  system.

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• A high rate of cutaneous blood flow
  (VD)
• ?
• ? heat conduction from core to skin
• ?
• ? heat loss as during exposure to
  hot environment

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• A low rate of cutaneous blood flow (VC)
• ?
• ? heat conduction from core to skin
• ?
• ? heat loss as during exposure to cold
  environment

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• The degree of VC or VD of arterioles and the
  anastomosis that supply blood to venous plexuses
  of the skin is controlled by
• VC is controlled by SNS.
• VD is controlled by local factors as
• heat metabolites( mainly )

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3. Rate of heat transfer from the skin to the
surroundings

• Radiation 60 - 70 of heat loss.
• Conduction 15 of heat loss.
• Evaporative heat loss
• - Latent heat of vaporization
• 580kcal/1Kg of water vaporized.
• so, amount of heat loss by evaporation
• 580kcal/h X amount of water
  evaporated

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• - Each ml of evaporated water removes
• with it 0.6 kcal.
• - Under resting conditions , 500 ml /day is
• evaporated , so , 500 X 0.6 300 kcal/
  day.
• - Heat loss by the skin is increased
  dramatically by sweating in hot dry climate
  and during muscular exercise.
• - Evaporative heat loss is the only mean of
  heat loss when the body is exposed to high
  ambient temperature.

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• 4. Convection.
• - It is the bulk of air movement surrounding
  the skin surface and is used as a way of heat
  loss
• - Convection also increases evaporative heat
  loss.
• - Also, it increases the degree of
  conduction.
• - Water has a higher heat conductivity than
  air.
• - Effect of clothing entraps air adjacent to
  the skin---- increases thickness of the private
  zone adjacent to the skin and decreases the flow
  of convection of air currents.

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Physiological Regulation of Heat Exchange
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• Rate of Heat Exchange with Environment depends
  on
• Skin temperature.
• - Different from one portion to
  another portion.
• - Skin, subcutaneous fat act as
  insulating blanket around the core of body
  protecting against heat loss or heat gain
  rapidly.
• - Skin temperature is determined by
• skin blood flow ( VC or VD ).

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• Rate of Sweat production
• Heat loss by evaporation is regulated by
  controlling the rate of sweat production by
• - Distributed all over the skin.
• - Innervated by sympathetic cholinergic
  fibers.
• - Stimulated by catecholamines (stress,
  anxiety)
• - Stimulated by aldosterone.
• - Blocked by atropine.
• - Controlled by hypothalamic center.

eccrine sweat gland
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• Mechanism of sweat secretion
• - Active process.
• - The deep subdermal coiled part secretes a
  precursor or primary secretion.
• - The duct portion of the gland modify the
  primary secretion in response to sympathetic
  cholinergic fibers.
• - Na Cl reabsorption in the ductal part
• under the effect of aldosterone.
• - Rate of sweat secretion 0-1.5 L/hour
  900Kcal/Hour.
• - Protein- free filtrate.

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• Composition of sweat secretion
• - Water 99.2.
• - Specific gravity 1001 1006.
• - PH 3.8 -- 6.5.
• - State of osmolarity hypotonic.
• - Na Concentration 142mEq/L.
• - Cl Concentration 104mEq/L.
• - Urea Concentration 0.02.
• - Lactic acid Concentration 0.3

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Central regulation of body temperature

• 1. Thermoreceptors
• - peripheral central
  receptors
• ?
• 2. Temperature regulating
  centers
• - Heat gain center
• - Heat loss center
• - Set point (36.5 37.2)
• ?
• 3. Effector organ system
• - Skin, skin blood vessels,
  sweat glands.
• - Skeletal muscles.
• - Endocrinal glands.

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• Neuronal Effector Mechanisms when the body
  exposed to hot environment
• To balance Heat production Heat loss.
• 1. ? Heat production.
• Inhibit shivering mechanism.
• Inhibit chemical thermogenesis.
• Decreased appetite (?food intake).
• 2. ? Heat loss.
• VD of skin blood vessels ? ?heat
  transfer to the skin as much as 8 fold.
• Sweating ? body temperature above
  critical body temperature 37.1ºC ?increased
  sweating ?? rate of evaporative heat loss.

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• Neuronal Effector Mechanisms when the body
  exposed to cold environment
• 1.? Heat production.
• Gradual increase in muscle tone.
• Hypothalamic stimulation of shivering.
• Chemical thermogenesis.
• Sympathetic excitation of heat
  production.
• Behavioral response
• - Moving into heated place.
• - Wearing suitable clothes.
• - Increased food intake.

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• 2. ? Heat loss
• VC of skin blood vessels through
  stimulation of posterior hypothalamus
  stimulation of SNS ??heat transfer to the skin.
• Piloerection is caused by sympathetic
  stimulation , not well developed in humans.

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• 2. Long period exposure to hot environment
• Adaptation to hot climate in 1-3 weeks.
• - ? sweat production from 1.5 14 L/h.
• - ? number of sweat ducts.
• - ? NaCl reabsorption and Kdepletion in sweat
  kidney under the effect of aldosterone to avoid
  heat exhaustion.

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• Exercise
• - Body temperature may rise 39.4 40.8ºC.
• - Profuse sweating marked skin VD.
• - Loss of salt and water into sweat and
  shunting of blood to the skin lead to heat
  cramps.
• - Extreme elevation of core temperature may
  cause heat exhaustion (shock and collapse due to
  excessive sweating, dehydration and
  hypovolaemia).

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• 2. Long period of exposure to cold environment
• ? Heat production
• - ? Catecholamines secretion.
• - ? Thyroxine.
• - ? Appetite fat storage mechanisms.
• ? Heat loss
• - Cutaneous VC.
• - Inhibit sweating mechanism.