Thermo Regulation 2

THERMOREGULATIONTHERMOREGULATION

Jakarta, November 1Jakarta, November 1stst 2012 2012

ByBy

dr. Mila Citrawati, M.Biomeddr. Mila Citrawati, M.Biomed

ThermoregulationThermoregulation

Human bodies have anatomical and Human bodies have anatomical and physiological mechanisms that keep body physiological mechanisms that keep body temperatures within acceptable limits, temperatures within acceptable limits, regardless of environmental conditions regardless of environmental conditions (homeothermic)(homeothermic)

Body temperature determines the rate of Body temperature determines the rate of many bodily activitiesmany bodily activities

A stable body temperature is the result of A stable body temperature is the result of heat loss and heat gain mechanismheat loss and heat gain mechanism

36,1 – 37,8 36,1 – 37,8 ºC ºC normal value normal value crucial crucial for the optimal performance of enzymatic for the optimal performance of enzymatic and regulatory activitiesand regulatory activities

A rise of only 1ºC increases the rate of A rise of only 1ºC increases the rate of chemical reaction by 10%chemical reaction by 10%

At restAt rest liver, heart, brain, endocrine liver, heart, brain, endocrine glands [>>heat generation], skeletal glands [>>heat generation], skeletal muscle [only 20-30%]muscle [only 20-30%]

Normal Body TemperatureNormal Body Temperature

Various parts of the body are at different Various parts of the body are at different temperatures and varies with the temperatures and varies with the environmental temperatureenvironmental temperature

Rectal Rectal ~ core temperature, oral ~ core temperature, oral 0,5°C 0,5°C lowerlower

Core temperature undergoes regular Core temperature undergoes regular circadian fluctuation of 0,5-0,7°Ccircadian fluctuation of 0,5-0,7°C

Women Women temperature variation temperature variation characterized by rise in basal temperature characterized by rise in basal temperature at the time of ovulationat the time of ovulation

Mechanisms of Heat TransferMechanisms of Heat Transfer

Radiation : transfer heat by infrared waves Radiation : transfer heat by infrared waves from a warmer object to a colder one from a warmer object to a colder one without the object being in contact [60%]without the object being in contact [60%]

Conduction : transfer heat from a warmer Conduction : transfer heat from a warmer object to a colder one in physical contact object to a colder one in physical contact with it [3%]with it [3%]

Convection : transfer heat by way of the Convection : transfer heat by way of the movement of liquid or gas to a colder area movement of liquid or gas to a colder area [15%][15%]

Heat LossHeat Loss

When the temperature at the preoptic When the temperature at the preoptic nucleus exceeds its thermostat setting, nucleus exceeds its thermostat setting, heat-loss center is stimulated, while heat-loss center is stimulated, while heat-gain center is inhibited heat-gain center is inhibited reflex reflex responses are controlled from anterior responses are controlled from anterior hypothalamushypothalamus

1. Inhibition of vasomotor center 1. Inhibition of vasomotor center vasodilatation peripheral blood vessels vasodilatation peripheral blood vessels skin becomes reddish skin becomes reddish skin skin temperature increase temperature increase radiation and radiation and convection rate increaseconvection rate increase

2. Sweat gland stimulated 2. Sweat gland stimulated perspiration perspiration flows across the body surface flows across the body surface evaporation rate increaseevaporation rate increase

3. Respiration centers are stimulated 3. Respiration centers are stimulated depth of respiration increase depth of respiration increase evaporation rate increaseevaporation rate increase

SummarySummary Body heat lost by : Radiation and Body heat lost by : Radiation and

conduction (70%), vaporization of sweat conduction (70%), vaporization of sweat (27%), respiration (2%), urination and (27%), respiration (2%), urination and defecation (1%)defecation (1%)

Mechanisms activated by heat : Increase Mechanisms activated by heat : Increase heat loss (cutaneous vasodilation, heat loss (cutaneous vasodilation, sweating, increased respiration) and sweating, increased respiration) and decrease heat production (anorexia, decrease heat production (anorexia, apathy, and inertia)apathy, and inertia)

Behavioral Mechanism to Loose Behavioral Mechanism to Loose HeatHeat

Looking for shady spot Looking for shady spot radiative gain radiative gain decreasedecrease

Lie down to cool grass, slide into pool, etc Lie down to cool grass, slide into pool, etc conductive losses increaseconductive losses increase

Heat GainHeat Gain

When temperature at preoptic nucleus When temperature at preoptic nucleus drops below acceptable levels, heat-gain drops below acceptable levels, heat-gain center is stimulated while heat-loss center center is stimulated while heat-loss center is inhibited is inhibited reflex responses are reflex responses are controlled from posterior hypothalamus controlled from posterior hypothalamus

Two mechanisms to gain heat :Two mechanisms to gain heat :

- heat conservationheat conservation

- heat generationheat generation

Heat ConservationHeat Conservation

Sympathetic vasomotor center decreases Sympathetic vasomotor center decreases blood flow to the dermis of the skin by blood flow to the dermis of the skin by vasoconstriction of peripheral blood vasoconstriction of peripheral blood vessels vessels reducing radiational, convective, reducing radiational, convective, and conductive lossesand conductive losses the skin cools , the skin cools , bluish or pale coloration. This does not bluish or pale coloration. This does not damage epithelial cells as they are able to damage epithelial cells as they are able to tolerate extended periods at temperatures tolerate extended periods at temperatures as low as 25as low as 25ºC or as high as 49ºCºC or as high as 49ºC

Countercurrent exchange; Countercurrent exchange;

when cutaneous blood vessels are cooled, when cutaneous blood vessels are cooled, they become more sensitive to they become more sensitive to catecholamine and the arterioles and catecholamine and the arterioles and venules constrict venules constrict directs blood away directs blood away from the skin and into the venae from the skin and into the venae comitantes, deep veins that run alongside comitantes, deep veins that run alongside the arteries the arteries heat is transferred from the heat is transferred from the arterial to the venous blood and carried arterial to the venous blood and carried back into the body without reaching the back into the body without reaching the skinskin

Contraction of errector pili muscle. Contraction of errector pili muscle. Piloerection causing the hairs to stand Piloerection causing the hairs to stand erect so convection is blocked, and erect so convection is blocked, and conduction through air is very slowconduction through air is very slow

Heat GenerationHeat Generation

Shivering thermogenesis: heat-gain center Shivering thermogenesis: heat-gain center activation activation stimulation of brain areas stimulation of brain areas controlling muscle tone controlling muscle tone muscle tone muscle tone increase increase stretch reflexes in antagonistic stretch reflexes in antagonistic muscle increase muscle increase shivering shivering heat heat production increase [shivering increases production increase [shivering increases the rate of heat generation by as much as the rate of heat generation by as much as 400%]400%]

Heat-gain center stimulates the adrenal Heat-gain center stimulates the adrenal medulla via sympathetic division of the medulla via sympathetic division of the ANS and epinephrine is released ANS and epinephrine is released cellular metabolism [glycogenolysis in liver cellular metabolism [glycogenolysis in liver & skeletal muscle] and the rate of aerobic & skeletal muscle] and the rate of aerobic respiration increaserespiration increase

Preoptic area directs the activity of thyroid Preoptic area directs the activity of thyroid gland gland thyrotropic hormone releasing thyrotropic hormone releasing factor increase factor increase thyrotropic hormone thyrotropic hormone release increase release increase thyroxine increase thyroxine increase cellular metabolism increase cellular metabolism increase heat heat production increaseproduction increase

Behavioral ModificationsBehavioral Modifications

Get into the sun [radiational heating]Get into the sun [radiational heating] Lie on warm sand [conduction heating]Lie on warm sand [conduction heating] Wearing sweater, gloves, jacket [reduce Wearing sweater, gloves, jacket [reduce

radiational surface area and increase radiational surface area and increase insulating]insulating]

Doing strenuous activityDoing strenuous activity

SummarySummary Body heat is produced by : Basic Body heat is produced by : Basic

metabolic processes, food intake, metabolic processes, food intake, muscular activitymuscular activity

Mechanisms activated by cold : Increase Mechanisms activated by cold : Increase heat production (shivering, hunger, heat production (shivering, hunger, increased voluntary activity, increased increased voluntary activity, increased secretion of norepinephrine and secretion of norepinephrine and epinephrine) and decrease heat loss epinephrine) and decrease heat loss (cutaneous vasoconstriction, curling up, (cutaneous vasoconstriction, curling up, horripilation)horripilation)

Maintaining the body temperatureMaintaining the body temperature

Keeping warm Staying cool

Increased insulation, subcutaneous fat reduces the conduction of heat from the body

Increase blood flow to skin, increases conduction and radiation of heat from the body

Reduced sweating decreases evaporation

Increased sweat secretion, increases evaporation

Increased shivering, increases heat produced by muscle tissue 2 to 5 times

Reduced activity

© 2008 Paul Billiet ODWS

nerves

Less heat generated

More water covers the skin.

More evaporation

Skin arteries dilateMore blood to the

skin. More radiation & conduction of heat

Muscles of skin arteriole

walls relaxSweat glands

increase secretion

Musclesreduce activity

Core body temperature

>37°C

Hypothalamus

Thermoreceptors


Thermoreceptors

Return to 37°C

Muscles of skin

arteriole walls relax


>37°CHypothalamus

Sweat glands

increase secretion

nerves

Musclesreduce activity

Thermoreceptors

NEGATIVE FEEDBACK

Blood temperature

Body loses heat


nerves

More heat generated

Less water covers the skin.

Less evaporation

Skin arteries constrict

Less blood to the skin.

Less radiation & conduction of heat

Muscles of skin arteriole

walls constrict

Sweat glands

decrease secretion

Musclesshivering

nerves


<37°C

Thermoreceptors

Hypothalamus


Thermoreceptors

Return to 37°C

NEGATIVE FEEDBACK

Blood temperature

Body loses less heat

Body gains heat

Muscles of skin

arteriole walls

constrict


<37°C

Sweat glands

decrease secretion

nerves

Musclesshivering

Thermoreceptors Hypothalamus

nerves


Temperature Homeostasis in Temperature Homeostasis in HumansHumans

Normal and Abnormal Variations in Normal and Abnormal Variations in Body TemperatureBody Temperature

Normal range [oral] Normal range [oral] 36-38 36-38ºC ºC systems systems normalnormal

Disease-related fever, severe exercise, active Disease-related fever, severe exercise, active children children 38-4138-41ºC ºC disorientation disorientation

CNS damage, heat stroke CNS damage, heat stroke >41ºC >41ºC cell cell damage, convulsion, tissue damage, deathdamage, convulsion, tissue damage, death

Early morning in cold weather, severe exposure Early morning in cold weather, severe exposure of cold of cold 36-32ºC 36-32ºC disorientation disorientation

Hypothermia for open heart surgery Hypothermia for open heart surgery 32-23ºC 32-23ºC loss of consciousness, cardiac arrest, skin loss of consciousness, cardiac arrest, skin turn to blue, deathturn to blue, death

Which mechanism of heat

transfer am I doing right now, guys?

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Thermo Regulation 2