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Temperature Regulation
Dr Dileep Verma Associate Professor Deptt of Physiology KGMU
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Lecture-1 :Topics Core and Shell body temp. Heat Balance
Factors promoting - a) Heat gain b) Heat loss Temp. regulatory mechanisms
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Learning Objectives Normal Body Temperature
Ways of measuring Body Temp List the mechanisms of heat production & heat loss Regulation of Body Temp.
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Body Temperature Normal Body Temperature (NBT) – 98.60F(370C)
Range of NBT (970F to 990F) Rectal Temp (0.50F to 10F) above the Oral Rectal Temp reflects the internal body Temp (Core Body Temp) Core Body Temp remain almost constant Skin Temp (Shell Temp)-----Variable
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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.
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Heat Balance Heat balance maintains the body temp
Balance between heat production & heat loss (Heat Balance) Heat Balance Heat production= Heat loss Heat production is called thermogenesis Heat loss is called as thermolysis
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Heat Production (Thermogenesis)
BMR Specific Dynamic Action of food Activity of skeletal muscle Shivering Exercise Chemical Thermogenesis Epinephrine &Norepinephrine Thyroxine Brown Fat- Source of considerable heat production Abundant in infants
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Heat Loss (Thermolysis)
Radiation Conduction Convection Evaporation Perspiration Respiration Loss through urine & feces
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Role of Skin
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Heat Exchange in the Skin
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Vasoconstriction and Vasodilatation
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Thermoregulation Temperature is regulated by nervous feedback mechanisms Thermoregulatory center located in the Hypothalamus Thermoregulatory regulatory responses include Autonomic Somatic Endocrine Behavioural changes
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Feedback 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
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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 blood temperature
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Thermoregulatory regulatory responses
Activated by Exposure to Cold Shivering Increase voluntary activity Increase TSH secretion Increase Catecholamines Vasoconstriction Horripilation Curling up
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Thermoregulatory regulatory responses
Activated by Exposure to Heat Vasodilatation Sweating Increase in Respiration Anorexia Apathy Decrease TSH secretion
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Thermoregulatory regulatory responses
Exposure to Cold Shivering Increase voluntary activity Increase TSH secretion Increase Catecholamines Vasoconstriction Horripilation Curling up Exposure to Heat Vasodilatation Sweating Increase in Respiration Anorexia Apathy Decrease TSH secretion
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1-A major source of heat production in infants is
Increased muscular activity Brown fat Increased sympathetic activity Specific dynamic action of food
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2-At normal room temperature most body heat loss is by-
Convention Conduction Radiation Sweating
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3-Constituents of secreted sweat are similar to plasma except for
Proteins Chloride Bicarbonate Potassium
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Radiation Conduction Convection Evaporation
4-The only available mechanism of heat transfer when the environmental temperature is greater than the body temperature is Radiation Conduction Convection Evaporation
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5-Cause of thermogenesis in the body is
Skeletal muscle relaxation Assimilation of food Decreased cardiac metabolism Hypothyroidism
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6-A major factor resulting in increase in body temperature during exercise is-
Heat dissipating mechanisms inefficient Enormous thermogenesis Vasoconstriction on non-working muscles Resetting of thermostat
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7-Site which reflects the true value of core temperature
Oesophagus and rectum Tympanic membrane Vagina All of the above
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8-BMR is dependent on Body weight Surface area
Amount of lean body mass Height
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9-One feels hotter on a humid day because-
Rate of sweating increases Surrounding temperature is more Heat loss by the body via process of radiation decreases Rate of evaporation of water from body decreases
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10-A major factor resulting in increase in body temperature during exercise is-
Heat dissipating mechanisms inefficient Enormous thermogenesis Vasoconstriction on non-working muscles Resetting of thermostat
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Temperature Regulation
Dr Dileep Verma Associate Professor Deptt of Physiology KGMU
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Lecture-2 :Topics Life in Hot environment -Effect of acute heat
Thermoregulatory responses Heat syndrome -Heat cramps -Heat exhaustion -Heat stroke
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Contd… Life in cold environment -effect of acute & long term
cold exposure on body Applied -Hypothermia -Harmful effects of extreme cold
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Learning Objectives Effect of Hot & Cold environment on the body.
Thermo-receptors Regulation of Body Temperature
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Life in Hot environment
Hot climates- These are two types a) Hot-dry b) Warm-humid Hot-dry climate- Found in deserts Temp >500 C Not humid Warm-humid climate – Found in tropical forest Temp usually<350 C Humidity >75%
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Effects of acute exposure to heat are divided into-
Contd---- Effects of acute heat - Effects of acute exposure to heat are divided into- a) Thermoregulatory responses b) Other effects
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Contd---- Vasodilatation Sweating Increase in Respiration Anorexia
Thermoregulatory regulatory responses Vasodilatation Sweating Increase in Respiration Anorexia Apathy Decrease TSH secretion
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Contd---- Other effects of acute heat exposure on- Cellular metabolism
Rate of respiration Work of breathing Pulse rate Dehydration Urinary volume
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Heat Syndromes- adverse reaction to heat exposure
Contd---- Heat Syndromes- adverse reaction to heat exposure a) Heat Cramps b) Heat Exhaustion c) Heat Stoke
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Life in cold environment
Effect of cold exposure on body- a) Acute cold exposure b) Long term cold exposure Applied -Hypothermia -Harmful effects of extreme cold
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Contd---- Effect of acute cold exposure on body
Shivering Increase voluntary activity Increase TSH secretion Increase Catecholamines Vasoconstriction Horripilation Curling up
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Effect of long term cold exposure Metabolic Responses
Contd---- Effect of long term cold exposure Metabolic Responses Insulative Responses Hypothermic Responses
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Hypothermia –Body temp below the normal lower limit (<970F)
Contd---- Hypothermia –Body temp below the normal lower limit (<970F) Thermoregulatory responses Greatly impaired at (<940F) Lost at body temp(<850F)
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Contd---- Frostbite Occurs at very low temp Common sites-
Surface area freezes Ice crystals formed Common sites- Lobes of the ears Digits of hands Digits of feet Cold induced vasodilatation- Final protection against frostbite
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Summary of Effector Mechanisms in Temperature Regulation
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1- Thermal sweating differs from non-thermal sweating in that
Eccrine glands are responsible for it Occurs due to activation of sympathetic cholinergic nerves Found mainly over palm, sole and axilla All of the above
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Core temperature of 260C leads to death due to:
Brain damage Respiratory insufficiency Cardiac failure All of the above
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2- Which area of hypothalamus functions as thermostat?
Preoptic Paraventricular Dorso medial Lateral
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3- Insensible water loss (perspiration) will be absent if humidity is
50% 70% 90% 100%
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4- Pyrogens raises body temperature by
Setting the thermostat to higher level Releasing interleukins Decreasing peripheral heat liberating mechanism Causing peripheral vasoconstriction
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5- Heat loss process of the body not directly under physiological control is
Radiation from body Conduction and convection to surroundings Vaporization of sweat Warming of inspired air
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6- Fever is usually caused by
Interleukin-1 Substance- p Endorphins Encephalin
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7- During exposure to cold, body temperature is raised by
Vasoconstriction in the skin Horripilation Thermogenesis All of the above
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8- Profound hypothermic signs include all except
Show breathing Bradycardia Hypotension Hyperactivity
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9- Aspirin decreases the body temperature by
Inhibiting interleukin-1 Inhibiting pyrogens release Killing fever producing organisms Inhibiting prostaglandin synthesis
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The blood vssels of the skin constrict
10- When the core temperature of the body falls below the hypothalamic set-point temperature The blood vssels of the skin constrict Heat production increases within minutes The basal metabolic rate increases All of the above
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