OBJECTIVESOBJECTIVES

11--Understand the basis of energy balanceUnderstand the basis of energy balance..

22--Define BMR and its significanceDefine BMR and its significance..

33--Respiratory QuotientRespiratory Quotient..

44--Understand the basis of thermal balanceUnderstand the basis of thermal balance..

55--Explain the thermoregulatory response to Explain the thermoregulatory response to cold and hot atmospherecold and hot atmosphere . .

Metabolism Metabolism AnabolismAnabolism Glucose + Energy---------GlycogenGlucose + Energy---------Glycogen CatabolismCatabolism Glycogen----------Glucose + ENERGYGlycogen----------Glucose + ENERGY

Energy in the form of ATPEnergy in the form of ATP ATP : combustion of food ATP : combustion of food stuffs ,carbohydrates, lipids, proteins.stuffs ,carbohydrates, lipids, proteins.Degradation of ATP → 24 kcal/molecule. Degradation of ATP → 24 kcal/molecule.

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

60%---------BMR.60%---------BMR.

8%----------Thermic effect of food & 8%----------Thermic effect of food &

cold cold ––induced thermogenesis.induced thermogenesis.

7%----------Spontaneous purposeless 7%----------Spontaneous purposeless activity.activity.

25%---------Purposeful physical activity.25%---------Purposeful physical activity.

Kilocalorie(Kcal): the amount of heat required to Kilocalorie(Kcal): the amount of heat required to raise the temperature of one Kg. of water from raise the temperature of one Kg. of water from 15-16 °C.15-16 °C.

( kcal= capital C)( kcal= capital C)

Kilocalorie = 1000 calorie.Kilocalorie = 1000 calorie.Physical heat value: the amount of energy Physical heat value: the amount of energy liberated when 1 gm. of substrate is completely liberated when 1 gm. of substrate is completely oxidized outside the bodyoxidized outside the bodyCaloric value of food ( physical heat value)Caloric value of food ( physical heat value)

CHO ------------4.1 C/gmCHO ------------4.1 C/gm Fats--------------9.3 C/gmFats--------------9.3 C/gm Protein-----------5.6 C/gmProtein-----------5.6 C/gm

The amount of energy liberated by 1 gm. of food The amount of energy liberated by 1 gm. of food substrate when they are completely oxidized substrate when they are completely oxidized inside the body. inside the body.

CHO--------------------4.0 C/gm.CHO--------------------4.0 C/gm. Fats----------------------9.0 C/gm.Fats----------------------9.0 C/gm. Protein------------------4.1 C/gm.Protein------------------4.1 C/gm. *** physiological heat value of protein (4.1) less *** physiological heat value of protein (4.1) less

than physical heat value( 5.6) due to incomplete than physical heat value( 5.6) due to incomplete oxidation of protein as complete oxidation lead oxidation of protein as complete oxidation lead to formation of nitric acid which is fatal.to formation of nitric acid which is fatal.

*** The difference between physical and *** The difference between physical and physiological values are due to variations in GIT physiological values are due to variations in GIT absorption, 98% CHO, 95% fats and 92% protein absorption, 98% CHO, 95% fats and 92% protein

Is the amount of heat generated when Is the amount of heat generated when 1 liter of oxygen used to oxidize 1 liter of oxygen used to oxidize different food stuffs.different food stuffs.

CHO produces 5 C.(kcal)CHO produces 5 C.(kcal)

Fat produces 4.7 C.(kcal)Fat produces 4.7 C.(kcal)

protein produces 4.5 C.( kcal)protein produces 4.5 C.( kcal)

Mixed food produces 4.8 C. (kcal)Mixed food produces 4.8 C. (kcal)

COCO22 production production

RQ RQ = --------------------- as a ratio= --------------------- as a ratio

OO22 consumption. consumption.

At rest:At rest:

OO22 consumption=250-300 ml/min(VO consumption=250-300 ml/min(VO22).).

COCO22 production =200-250ml/min(VCO production =200-250ml/min(VCO22).).

Importance of RQImportance of RQ::1.1. Determines the nature of food substance oxidized in different Determines the nature of food substance oxidized in different

tissues and under tissues and under different conditions.different conditions. CHO ------------RQ=1.CHO ------------RQ=1. Fat---------------RQ=0.7.Fat---------------RQ=0.7. Protein-----------RQ=0.8.Protein-----------RQ=0.8.2.2. Transformation of one food substance into another one.Transformation of one food substance into another one. CHO(O2 CHO(O2 –– rich) ----------------Fat (O2-poor)----------------------more rich) ----------------Fat (O2-poor)----------------------more

CO2 production so higher RQ.CO2 production so higher RQ.3. Determines the caloric value of O2 using special metabolic tables.3. Determines the caloric value of O2 using special metabolic tables.4. Denotes the type of food utilization after their absorption 4. Denotes the type of food utilization after their absorption If RQ=1 ----------CHO utilization.If RQ=1 ----------CHO utilization. If RQ=0.7---------Fat utilization.If RQ=0.7---------Fat utilization.5. Negative RQ:( arterial CO5. Negative RQ:( arterial CO22 > venous CO > venous CO22 ) as in ) as in - HCL secretion in stomach.- HCL secretion in stomach. - HCO3 secretion in pancreas- HCO3 secretion in pancreas - Formation of intraocular formation.- Formation of intraocular formation. - Utilization of CO- Utilization of CO22 by the kidney to get red of H by the kidney to get red of H++..

The absolute minimal energy expenditure The absolute minimal energy expenditure of the body to exist under basal of the body to exist under basal conditions.conditions.Criteria of basal conditions:Criteria of basal conditions:

* at the morning.* at the morning. *12-14 after the last meal.*12-14 after the last meal. *Complete physical and mental rest.*Complete physical and mental rest. *Resting and supine position.*Resting and supine position. *Comfortable temperature 20-25°C.*Comfortable temperature 20-25°C. *Normal body temperature.*Normal body temperature.

1. Generating & maintaining ionic 1. Generating & maintaining ionic gradients and other molecules gradients and other molecules across membranes.across membranes.

2. The mechanical work of respiration.2. The mechanical work of respiration.3. Circulation of blood.3. Circulation of blood.4. Production of muscle tone, signals 4. Production of muscle tone, signals

conduction in nervous system.conduction in nervous system.5. Obligate heat loss via body surfaces 5. Obligate heat loss via body surfaces

to the environment.to the environment.

Factors affecting BMRFactors affecting BMR1.1. Physiological factors:Physiological factors:

* Age:* Age:

Newborn= 25C/H/MNewborn= 25C/H/M22

Age2-5 years=60C/H/MAge2-5 years=60C/H/M22

Age 20 years=40C/H/MAge 20 years=40C/H/M22

Above 20 years → Decreased 1C/10 Above 20 years → Decreased 1C/10 years.years.

* Sex:* Sex:

BMR is lower in female by about 7%BMR is lower in female by about 7%

due to more fat store with little due to more fat store with little metabolic activity. metabolic activity.

Normal value of BMRNormal value of BMR:: In adult man 40 C/H/M2 ± 15%In adult man 40 C/H/M2 ± 15%. .

Clinical expression of BNRClinical expression of BNR:: Expressed as a % of increase or decrease Expressed as a % of increase or decrease

fromfrom the normal standard value for the subjectthe normal standard value for the subject..

e.g. If BMR = 60 C/H/M2( + 20 C/H/M2)e.g. If BMR = 60 C/H/M2( + 20 C/H/M2) Exceeding the normal standard value Exceeding the normal standard value

by 20by 20 so, +50% ( higher than normal value so, +50% ( higher than normal value

i.ei.e.. 15%15% for his age and sexfor his age and sex))

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

* Physical habits:* Physical habits:

# Athletes have BMR about 10%# Athletes have BMR about 10%

higher than in sedentary due tohigher than in sedentary due to

more muscle bulk and lessermore muscle bulk and lesser

amount of fat stores.amount of fat stores.

* Dietetic habit:* Dietetic habit:

# prolonged ingestion of protein# prolonged ingestion of protein

increases BMR 10% more thanincreases BMR 10% more than

eating CHO. or mixed diet.eating CHO. or mixed diet.

* Pregnancy:* Pregnancy:

# pregnant women have higher# pregnant women have higher

BMR than non pregnant due toBMR than non pregnant due to

additional metabolism of fetus.additional metabolism of fetus.

* Anxiety & stress:* Anxiety & stress:

# Higher BMR due to increase# Higher BMR due to increase

the level of stress hormone;the level of stress hormone;

adrenaline, noradrenaline,adrenaline, noradrenaline,

cortisone.cortisone.

* Sleep:* Sleep:

# Lower BMR by 10-15% due to # Lower BMR by 10-15% due to

- Decreased skeletal muscle - Decreased skeletal muscle

tone.tone.

- Decreased activity of SNS.- Decreased activity of SNS.

2. Pathological factors:2. Pathological factors:

# Higher BMR,# Higher BMR,

. Hyperthyroidism up to 100%. Hyperthyroidism up to 100%

. Hyperpituitarism due to . Hyperpituitarism due to

- G.H. - TSH - G.H. - TSH

. Hyperadrenalism : due to more. Hyperadrenalism : due to more

secretion of catecholamines.secretion of catecholamines.

. Hyperpyrexia: Higher BMR by . Hyperpyrexia: Higher BMR by

10-14% for each 1°C rise in body10-14% for each 1°C rise in body

temperature.temperature.

. Heart failure: Higher BMR due to . Heart failure: Higher BMR due to

increase activity of respiratoryincrease activity of respiratory

muscles.muscles.

. Diabetes insipidus: Higher BMR. Diabetes insipidus: Higher BMR

to maintain body temperature.to maintain body temperature.

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

3. Chemical factors:3. Chemical factors:

* Hormones,* Hormones,

# Thyroid h.: most stimulant.# Thyroid h.: most stimulant.

# TSH # Adrenaline# TSH # Adrenaline

# ACTH & cortisone.# ACTH & cortisone.

# G.H. : increase BMR 15-20%# G.H. : increase BMR 15-20%

due to direct stimulation of due to direct stimulation of

cellular metabolism.cellular metabolism.

# Male sex h.: increase BMR # Male sex h.: increase BMR

10-15%.10-15%.

* Drugs:* Drugs:

# Caffeine:# Caffeine:

- Central stimulant action.- Central stimulant action.

- Increase CAMP.- Increase CAMP.

# Antithyroid agents :# Antithyroid agents :

- block production of thyroid h.- block production of thyroid h.

# Alcohol:# Alcohol:

- Increase heat loss due to - Increase heat loss due to

cutaneous V.D. so ↑ BMR tocutaneous V.D. so ↑ BMR to

maintain body temperature.maintain body temperature.

The body temperature of human The body temperature of human body is maintained within 0.6° C of body is maintained within 0.6° C of its normal value 37.0 °C(98 °F) .its normal value 37.0 °C(98 °F) .

Constant body temperature is Constant body temperature is essential for optimum enzymatic essential for optimum enzymatic activity.activity.

Homeostasis depends upon the Homeostasis depends upon the balance between heat gain & heat balance between heat gain & heat output.output.

1.1. Diurnal RhythmDiurnal Rhythm

↓ ↓ in the morning→↑ in the early in the morning→↑ in the early afternoon→↑ in the midafternoonafternoon→↑ in the midafternoon

( maximum activity).( maximum activity).

2.2. Children have higher temperature .Children have higher temperature .

3.3. Adult women show body temperature Adult women show body temperature changes related to menstrual cycle.changes related to menstrual cycle.

4. Prolonged inactivity & exposure to 4. Prolonged inactivity & exposure to cold environment →↓body cold environment →↓body temperature.temperature.

5. Emotional stress, muscular exercise, 5. Emotional stress, muscular exercise, activity, and exposure to hot activity, and exposure to hot environment environment

→↑ →↑ body temperature.body temperature.

6. Febrile illness & state of thyroid 6. Febrile illness & state of thyroid gland affect body temperature.gland affect body temperature.

1.1. Core temperature.Core temperature. Site: Deep organsSite: Deep organs ----- almost keep constant.----- almost keep constant. ----- Oral, Rectal,Axillary routes.----- Oral, Rectal,Axillary routes. ----- Oral < Rectal by o.5°C----- Oral < Rectal by o.5°C ----- Axillary < Rectal by 1°C----- Axillary < Rectal by 1°C ----- Rectal is the most accurate route.----- Rectal is the most accurate route. ----- Ranges between ( morning oral ) ----- Ranges between ( morning oral )

36.5 36.5 –– 37.2°C at room 37.2°C at room temperature 24 -25°C.temperature 24 -25°C.

2. Skin temperature:2. Skin temperature:

----- Surface temperature.----- Surface temperature.

----- Fluctuates with ambient ----- Fluctuates with ambient temperature.temperature.

----- Highest in areas of head , ----- Highest in areas of head , chest ,and abdomen 34°C, big chest ,and abdomen 34°C, big muscles 30°C and small muscles 30°C and small muscles,28°C. muscles,28°C.

Thermal balance

Heat gain Heat loss

1.1. Heat production:Heat production: . BMR.. BMR. . Exercise.. Exercise. . Specific dynamic action (SDA).. Specific dynamic action (SDA). . Extra- metabolism by:. Extra- metabolism by: * Thyroxine.* Thyroxine. * Growth hormone & testosterone.* Growth hormone & testosterone. * Sympathetic nervous system.* Sympathetic nervous system. * Cell activity.* Cell activity.2.2. Heat uptake :Heat uptake : . Ambient temperature > Skin temperature.. Ambient temperature > Skin temperature.

1.1. Most of heat loss is produced by Most of heat loss is produced by deep organs especially liver, deep organs especially liver, brain ,heart and skeletal muscles.brain ,heart and skeletal muscles.

2.2. Conveyed to the surface through Conveyed to the surface through the tissues to the skin only if the the tissues to the skin only if the skin temperature is < core skin temperature is < core temperature.temperature.

Rate of heat Loss depends upon :Rate of heat Loss depends upon :

1.1. Rate of heat production by the Rate of heat production by the body tissues. body tissues.

2. Rate of heat conduction from 2. Rate of heat conduction from deep organs to skin.deep organs to skin.

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

1.1. Skin blood supply( cutaneous Skin blood supply( cutaneous blood supply).blood supply).

Source of heat production:Source of heat production: * In 70-kg normal person, Energy * In 70-kg normal person, Energy

requirements = requirements = At rest ====== 75 At rest ====== 75 –– 80 Kcal / hour. 80 Kcal / hour. During exercise ==== 1400 Kcal/ hour.During exercise ==== 1400 Kcal/ hour.1.1. Behavioral responses,Behavioral responses, - in cold weather ---- increased food - in cold weather ---- increased food

intake.intake. - in hot weather ---- decreased food - in hot weather ---- decreased food

intake. intake.

2. Physiological responses,2. Physiological responses, a) Muscle tone:a) Muscle tone: - increased gradually by signals from hypothalamus, ↑ MR - increased gradually by signals from hypothalamus, ↑ MR

up to 50 up to 50 –– 100 %. 100 %. b) Shivering:b) Shivering: - It is involuntary response to a fall in core body - It is involuntary response to a fall in core body

temperature.temperature. - It can be stopped or reduced by voluntary pathways.- It can be stopped or reduced by voluntary pathways. - It is characterized by , not rhythmic , no actual muscle - It is characterized by , not rhythmic , no actual muscle

shaking, gradually increase in MT above a certain level leads shaking, gradually increase in MT above a certain level leads to shivering begins( asynchronous contraction and to shivering begins( asynchronous contraction and relaxation of small antagonistic muscle groups a rate of relaxation of small antagonistic muscle groups a rate of about 10 about 10 –– 20 / second. 20 / second.

- It is controlled via hypothalamic signals.- It is controlled via hypothalamic signals. - Most of energy is transformed into heat, since no external - Most of energy is transformed into heat, since no external

work is done.work is done. - It can be abolished by ,alcohol,crure.- It can be abolished by ,alcohol,crure. - It can be induced by ingestion of cold food. - It can be induced by ingestion of cold food.

3. Endocrinal responses( chemical 3. Endocrinal responses( chemical thermogenesis) :thermogenesis) :

a) Catecholamines & SNS excitation.a) Catecholamines & SNS excitation. -↑MR by uncoupling phosphorylation-↑MR by uncoupling phosphorylation - ↑FFA release of fat stores- ↑FFA release of fat stores - VC of skin blood vessels→↓ heat loss- VC of skin blood vessels→↓ heat loss - Stimulate glycogenolysis in liver- Stimulate glycogenolysis in liver b) Thyroid hormone.b) Thyroid hormone. - Long exposure to cold stimulate - Long exposure to cold stimulate thyroid hormone secretion →↑MR bythyroid hormone secretion →↑MR by uncoupling phosphorylation.uncoupling phosphorylation.

c) Hypothalamic hormone.c) Hypothalamic hormone.

- TSH.- TSH.

- ACTH & Glucocorticoids.- ACTH & Glucocorticoids.

- ADH.- ADH.

d) Effect of clothing.d) Effect of clothing.

- Protect the body against heat - Protect the body against heat loss.loss.

- Clothes act as air traps which is - Clothes act as air traps which is a bad a bad conductor of heat.conductor of heat.

22 - -Rate of heat conduction from Rate of heat conduction from deep organs to the skindeep organs to the skin

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

* A high rate of cutaneous blood * A high rate of cutaneous blood flow (VD)flow (VD)

↓ ↓

↑ ↑ heat conduction from core to heat conduction from core to skinskin

↓ ↓

↑ ↑ heat loss as during exposure to heat loss as during exposure to hot environment hot environment

A low rate of cutaneous blood flow A low rate of cutaneous blood flow (VC)(VC)

↓ ↓

↓ ↓ heat conduction from core to skinheat conduction from core to skin

↓ ↓

↓ ↓ heat loss as during exposure to heat loss as during exposure to cold environment cold environment

* The degree of VC or VD of arterioles * The degree of VC or VD of arterioles and the anastomosis that supply and the anastomosis that supply blood to venous plexuses of the skin blood to venous plexuses of the skin is controlled by :is controlled by :

* VC is controlled by SNS.* VC is controlled by SNS.

* VD is controlled by local factors * VD is controlled by local factors as as

heat & metabolites( mainly )heat & metabolites( mainly )

33 . .Rate of heat transfer from the Rate of heat transfer from the skin to the surroundingsskin to the surroundings

1.1. Radiation 60 - 70 % of heat loss.Radiation 60 - 70 % of heat loss.

2.2. Conduction 15% of heat loss.Conduction 15% of heat loss.

3.3. Evaporative heat loss :Evaporative heat loss :

- Latent heat of vaporization- Latent heat of vaporization

=580kcal/1Kg of water vaporized.=580kcal/1Kg of water vaporized.

so, amount of heat loss by evaporationso, amount of heat loss by evaporation

=580kcal/h X amount of water =580kcal/h X amount of water evaporated evaporated

- Each ml of evaporated water removes - Each ml of evaporated water removes with it 0.6 kcal.with it 0.6 kcal. - Under resting conditions , 500 ml /day is- Under resting conditions , 500 ml /day is evaporated , so , 500 X 0.6 = 300 kcal/ evaporated , so , 500 X 0.6 = 300 kcal/

day.day. - Heat loss by the skin is increased - Heat loss by the skin is increased

dramatically by dramatically by –– sweating in hot dry sweating in hot dry climate climate and during muscular exercise.and during muscular exercise.

- Evaporative heat loss is the only mean of - Evaporative heat loss is the only mean of heat loss when the body is exposed to heat loss when the body is exposed to high ambient temperature.high ambient temperature.

4. Convection.4. Convection. - It is the bulk of air movement surrounding the - It is the bulk of air movement surrounding the

skin surface and is used as a way of heat skin surface and is used as a way of heat lossloss - Convection also increases evaporative heat - Convection also increases evaporative heat

loss.loss. - Also, it increases the degree of conduction.- Also, it increases the degree of conduction. - Water has a higher heat conductivity than air. - Water has a higher heat conductivity than air. - Effect of clothing: entraps air adjacent to the - Effect of clothing: entraps air adjacent to the

skin---- increases thickness of the private zone skin---- increases thickness of the private zone adjacent to the skin and decreases the flow of adjacent to the skin and decreases the flow of convection of air currents.convection of air currents.

Physiological Regulation of Heat Physiological Regulation of Heat ExchangeExchange

HUMAN BODYEnvironmentalTemperature

Rate of Heat Exchange with Environment Rate of Heat Exchange with Environment depends on :depends on :

* Skin temperature.* Skin temperature.

- Different from one portion to - Different from one portion to another portion.another portion.

- Skin, subcutaneous fat act as - Skin, subcutaneous fat act as insulating blanket around the core of body insulating blanket around the core of body protecting against heat loss or heat gain protecting against heat loss or heat gain rapidly.rapidly.

- Skin temperature is determined by - Skin temperature is determined by

skin blood flow ( VC or VD ). skin blood flow ( VC or VD ).

* Rate of Sweat production:* Rate of Sweat production: Heat loss by evaporation is regulated by controlling Heat loss by evaporation is regulated by controlling

the rate of sweat production by the rate of sweat production by

- Distributed all over the skin.- Distributed all over the skin. - Innervated by sympathetic cholinergic fibers.- Innervated by sympathetic cholinergic fibers. - Stimulated by catecholamines (stress, anxiety)- Stimulated by catecholamines (stress, anxiety) - Stimulated by aldosterone.- Stimulated by aldosterone. - Blocked by atropine.- Blocked by atropine. - Controlled by hypothalamic center.- Controlled by hypothalamic center.

* Mechanism of sweat secretion:* Mechanism of sweat secretion: - Active process.- Active process. - The deep subdermal coiled part secretes - The deep subdermal coiled part secretes

a precursor or primary secretion.a precursor or primary secretion. - The duct portion of the gland modify the - The duct portion of the gland modify the

primary secretion in response to primary secretion in response to sympathetic sympathetic cholinergic fibers.cholinergic fibers.

- Na & Cl reabsorption in the ductal part - Na & Cl reabsorption in the ductal part under the effect of aldosterone.under the effect of aldosterone. - Rate of sweat secretion 0-1.5 L/hour= - Rate of sweat secretion 0-1.5 L/hour=

900Kcal/Hour.900Kcal/Hour. - Protein- free filtrate. - Protein- free filtrate.

* Composition of sweat secretion :* Composition of sweat secretion :

- Water : 99.2%.- Water : 99.2%.

- Specific gravity : 1001 - Specific gravity : 1001 –– 1006. 1006.

- PH : 3.8 -- 6.5.- PH : 3.8 -- 6.5.

- State of osmolarity : hypotonic.- State of osmolarity : hypotonic.

- Na- Na++ Concentration : 142mEq/L. Concentration : 142mEq/L.

- Cl- Cl Concentration : 104mEq/L. Concentration : 104mEq/L.

- Urea Concentration : 0.02%.- Urea Concentration : 0.02%.

- Lactic acid Concentration : 0.3% - Lactic acid Concentration : 0.3%

1.1. Thermoreceptors Thermoreceptors - peripheral & central receptors - peripheral & central receptors ↓ ↓ 2. Temperature 2. Temperature –– regulating centers regulating centers - Heat - Heat –– gain center gain center - Heat - Heat –– loss center loss center - Set - Set –– point (36.5 point (36.5 –– 37.2) 37.2) ↓ ↓ 3. Effector organ system3. Effector organ system - Skin, skin blood vessels, sweat glands.- Skin, skin blood vessels, sweat glands. - Skeletal muscles.- Skeletal muscles. - Endocrinal glands.- Endocrinal glands.

Neuronal Effector Mechanisms when the Neuronal Effector Mechanisms when the body exposed to hot environment:body exposed to hot environment:

To balance Heat production = Heat loss.To balance Heat production = Heat loss. 1. ↓ Heat production.1. ↓ Heat production. * Inhibit shivering mechanism.* Inhibit shivering mechanism. * Inhibit chemical thermogenesis.* Inhibit chemical thermogenesis. * Decreased appetite (↓food intake).* Decreased appetite (↓food intake). 2. ↑ Heat loss.2. ↑ Heat loss. * VD of skin blood vessels → ↑heat * VD of skin blood vessels → ↑heat

transfer to the skin as much as 8 fold.transfer to the skin as much as 8 fold. * Sweating : ↑ body temperature * Sweating : ↑ body temperature

above above critical body temperature 37.1critical body temperature 37.1ººC C →increased →increased sweating →↑ rate of sweating →↑ rate of evaporative heat loss. evaporative heat loss.

Neuronal Effector Mechanisms when the Neuronal Effector Mechanisms when the body exposed to cold environment:body exposed to cold environment:

1.↑ Heat production.1.↑ Heat production. * Gradual increase in muscle tone.* Gradual increase in muscle tone. * Hypothalamic stimulation of shivering.* Hypothalamic stimulation of shivering. * Chemical thermogenesis.* Chemical thermogenesis. * Sympathetic excitation of heat * Sympathetic excitation of heat

production.production. * Behavioral response:* Behavioral response: - Moving into heated place.- Moving into heated place. - Wearing suitable clothes.- Wearing suitable clothes. - Increased food intake. - Increased food intake.

2. ↓ Heat loss:2. ↓ Heat loss:

* VC of skin blood vessels through * VC of skin blood vessels through stimulation of posterior hypothalamus stimulation of posterior hypothalamus stimulation of SNS →↓heat transfer to stimulation of SNS →↓heat transfer to the skin.the skin.

* Piloerection: is caused by sympathetic * Piloerection: is caused by sympathetic stimulation , not well developed in stimulation , not well developed in humans.humans.

2. Long period exposure to hot 2. Long period exposure to hot environment environment

Adaptation to hot climate in 1-3 weeks.Adaptation to hot climate in 1-3 weeks.

- ↑ sweat production from 1.5 - ↑ sweat production from 1.5 –– 14 L/h. 14 L/h.

- ↑ number of sweat ducts.- ↑ number of sweat ducts.

- ↑ NaCl reabsorption and K- ↑ NaCl reabsorption and K++depletion in depletion in sweat &kidney under the effect of sweat &kidney under the effect of aldosterone to avoid heat exhaustion. aldosterone to avoid heat exhaustion.

* Exercise:* Exercise:

- Body temperature may rise 39.4 - Body temperature may rise 39.4 –– 40.840.8ººC.C.

- Profuse sweating &marked skin VD.- Profuse sweating &marked skin VD.

- Loss of salt and water into sweat and - Loss of salt and water into sweat and shunting of blood to the skin lead to shunting of blood to the skin lead to heat cramps.heat cramps.

- Extreme elevation of core - Extreme elevation of core temperature may cause heat temperature may cause heat exhaustion (shock and collapse due to exhaustion (shock and collapse due to excessive sweating, dehydration and excessive sweating, dehydration and hypovolaemia).hypovolaemia).

2. Long period of exposure to cold 2. Long period of exposure to cold environment:environment:

* ↑ Heat production:* ↑ Heat production:

- ↑ Catecholamines secretion.- ↑ Catecholamines secretion.

- ↑ Thyroxine.- ↑ Thyroxine.

- ↑ Appetite & fat storage - ↑ Appetite & fat storage mechanisms.mechanisms.

* ↓ Heat loss:* ↓ Heat loss:

- Cutaneous VC.- Cutaneous VC.

- Inhibit sweating mechanism.- Inhibit sweating mechanism.