Temperature RegulationTemperature Regulation

Dr Dileep Verma Associate Professor Deptt of Physiology KGMU

Lecture-1 :TopicsLecture-1 :Topics

Core and Shell body temp.

Heat Balance

Factors promoting -

a) Heat gain

b) Heat loss

Temp. regulatory mechanisms

Learning ObjectivesLearning Objectives

Normal Body Temperature

Ways of measuring Body Temp

List the mechanisms of heat

production & heat loss

Regulation of Body Temp.

Body TemperatureBody TemperatureNormal Body Temperature (NBT) –

98.60F(370C)Range of NBT ----- (970F to 990F)Rectal Temp ----- (0.50F to 10F) above

the OralRectal Temp reflects the internal body

Temp (Core Body Temp)Core Body Temp remain almost constantSkin Temp (Shell Temp)-----Variable

Temperature Homeostasis

Keep the body temp within a very narrow range

Range of NBT (970F to 990F)

Temperatures above this:denature enzymes and block metabolic pathways

Temperatures below this:slow down metabolism and affect the brain.

Heat BalanceHeat balance maintains the body

tempBalance between heat production

& heat loss (Heat Balance)Heat Balance

Heat production= Heat loss

Heat production is called thermogenesis

Heat loss is called as thermolysis

Heat Production (Thermogenesis)

BMRSpecific Dynamic Action of foodActivity of skeletal muscle

Shivering Exercise

Chemical Thermogenesis Epinephrine &Norepinephrine ThyroxineBrown Fat- Source of considerable heat

production Abundant in infants

Heat Loss (Thermolysis)

RadiationConductionConvectionEvaporationPerspirationRespirationLoss through urine & feces

Role of SkinRole of Skin

Heat Exchange in the SkinHeat Exchange in the Skin

Vasoconstriction and Vasoconstriction and VasodilatationVasodilatation

Thermoregulation

Temperature is regulated by nervous feedback mechanisms

Thermoregulatory center located in the Hypothalamus

Thermoregulatory regulatory responses include

AutonomicSomatic

Endocrine Behavioural changes

Feedback systemFeedback system

1) Receptor◦Sensor that responds to changes (stimuli)

2) Control Center◦Sets range of values ◦Evaluates input and◦ Sends output

3) Effector-◦Receives output from control centre ◦Produces a response

Body Temperature Control System

Hypothalamus◦ Acts as a thermostat

◦ Receives nerve impulses from cutaneous thermoreceptors

◦ Thermoreceptors Cold &Heat

Hypothalamus- also has thermoreceptors called central thermoreceptors

These detect changes in These detect changes in blood temperatureblood temperature

Thermoregulatory regulatory responses

Activated by Exposure to Cold

1. Shivering2. Increase voluntary activity3. Increase TSH secretion4. Increase Catecholamines5. Vasoconstriction6. Horripilation7. Curling up

Thermoregulatory regulatory responses

Activated by Exposure to Heat

1. Vasodilatation2. Sweating3. Increase in Respiration4. Anorexia5. Apathy6. Decrease TSH secretion

Thermoregulatory regulatory responses

Exposure to ColdShivering

Increase voluntary activity

Increase TSH secretion

Increase Catecholamines

Vasoconstriction

Horripilation

Curling up

Exposure to HeatVasodilatation

Sweating

Increase in Respiration

Anorexia

Apathy

Decrease TSH secretion

1-A major source of heat production in infants isA. Increased muscular activityB. Brown fatC. Increased sympathetic activityD. Specific dynamic action of food

2-At normal room temperature most body heat loss is by-

A.ConventionB.ConductionC. Radiation D.Sweating

3-Constituents of secreted sweat are similar to plasma except for

A. ProteinsB. ChlorideC. BicarbonateD. Potassium

4-The only available mechanism of heat transfer when the environmental temperature is greater than the body temperature is

A. RadiationB. ConductionC. ConvectionD. Evaporation

5-Cause of thermogenesis in the body is

A. Skeletal muscle relaxationB. Assimilation of foodC. Decreased cardiac metabolismD. Hypothyroidism

6-A major factor resulting in increase in body temperature during exercise is-

A. Heat dissipating mechanisms inefficient

B. Enormous thermogenesisC. Vasoconstriction on non-

working musclesD. Resetting of thermostat

7-Site which reflects the true value of core temperature

A. Oesophagus and rectumB. Tympanic membraneC.VaginaD.All of the above

8-BMR is dependent on

A. Body weight B. Surface areaC. Amount of lean body mass D. Height

9-One feels hotter on a humid day because-

A. Rate of sweating increases B. Surrounding temperature is

moreC. Heat loss by the body via

process of radiation decreasesD. Rate of evaporation of water

from body decreases

10-A major factor resulting in increase in body temperature during exercise is-

A. Heat dissipating mechanisms inefficient

B. Enormous thermogenesisC. Vasoconstriction on non-

working musclesD. Resetting of thermostat

Temperature RegulationTemperature Regulation

Dr Dileep Verma Associate Professor Deptt of Physiology KGMU

Lecture-2 :TopicsLecture-2 :Topics

Life in Hot environment -Effect of acute heatThermoregulatory responsesHeat syndrome -Heat cramps -Heat exhaustion -Heat stroke

Contd…Contd…

Life in cold environment -effect of acute & long term cold exposure on bodyApplied -Hypothermia -Harmful effects of extreme cold

Learning ObjectivesLearning Objectives

Effect of Hot & Cold environment on

the body.

Thermo-receptors

Regulation of Body Temperature

Life in Hot environment

Hot climates- These are two typesa) Hot-dryb) Warm-humid

Hot-dry climate- Found in deserts Temp >500 C Not humid Warm-humid climate –

Found in tropical forest Temp usually<350 CHumidity >75%

Contd----Contd----

Effects of acute heat - Effects of acute exposure to heat

are divided into-

a) Thermoregulatory responses

b) Other effects

Contd----Contd----

Thermoregulatory regulatory responses

VasodilatationSweatingIncrease in RespirationAnorexiaApathyDecrease TSH

secretion

Contd----Contd----

Other effects of acute heat exposure on-

Cellular metabolism

Rate of respiration

Work of breathing

Pulse rate

Dehydration

Urinary volume

Contd----Contd----

Heat Syndromes- adverse reaction to heat exposure

a) Heat Crampsb) Heat

Exhaustionc) Heat Stoke

Life in cold environmentEffect of cold exposure on body-

a) Acute cold exposure b) Long term cold exposure

Applied -Hypothermia -Harmful effects of extreme cold

Contd----Contd----

Effect of acute cold exposure on body

ShiveringIncrease voluntary activityIncrease TSH secretionIncrease CatecholaminesVasoconstrictionHorripilationCurling up

Contd----Contd----

Effect of long term cold exposure

Metabolic Responses Insulative Responses Hypothermic Responses

Contd----Contd----

Hypothermia –Body temp below the normal lower limit (<970F)

Thermoregulatory responses Greatly impaired at

(<940F)

Lost at body temp(<850F)

Contd----Contd----Frostbite

Occurs at very low tempSurface area freezesIce crystals formed

Common sites- Lobes of the earsDigits of handsDigits of feet

Cold induced vasodilatation- Final protection against

frostbite

Summary of Effector Mechanisms Summary of Effector Mechanisms in Temperature Regulationin Temperature Regulation

1- Thermal sweating differs from non-thermal sweating in that

A. Eccrine glands are responsible for it

B. Occurs due to activation of sympathetic cholinergic nerves

C. Found mainly over palm, sole and axilla

D. All of the above

Core temperature of 260C leads to death due to:

a) Brain damage b) Respiratory insufficiencyc) Cardiac failured) All of the above

2- Which area of hypothalamus functions as thermostat?

A. PreopticB. ParaventricularC. Dorso medial D. Lateral

3- Insensible water loss (perspiration) will be absent if humidity is

A. 50%B. 70%C. 90%D. 100%

4- Pyrogens raises body temperature by

A. Setting the thermostat to higher level

B. Releasing interleukinsC. Decreasing peripheral heat

liberating mechanismD. Causing peripheral vasoconstriction

5- Heat loss process of the body not directly under physiological control is

A. Radiation from body B. Conduction and convection to

surroundingsC. Vaporization of sweatD. Warming of inspired air

6- Fever is usually caused by

A. Interleukin-1B. Substance- pC. EndorphinsD. Encephalin

7- During exposure to cold, body temperature is raised by

A. Vasoconstriction in the skinB. HorripilationC. ThermogenesisD. All of the above

8- Profound hypothermic signs include all except

A. Show breathingB. BradycardiaC. HypotensionD. Hyperactivity

9- Aspirin decreases the body temperature by

A. Inhibiting interleukin-1B. Inhibiting pyrogens releaseC. Killing fever producing organisms D. Inhibiting prostaglandin synthesis

10- When the core temperature of the body falls below the hypothalamic set-point temperature

A. The blood vssels of the skin constrict

B. Heat production increases within minutes

C. The basal metabolic rate increasesD. All of the above