Temperature Regulation

1. Temperature Regulation
Dr Dileep Verma
Associate Professor
Deptt of Physiology
KGMU

2. Lecture-1 :Topics
 Core and Shell body temp.
 Heat Balance
 Factors promoting -
a) Heat gain
b) Heat loss
 Temp. regulatory mechanisms

3. Learning Objectives
 Normal Body Temperature
 Ways of measuring Body Temp
 List the mechanisms of heat
production & heat loss
 Regulation of Body Temp.

4. 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

5. 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.

6. 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

8. 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

9. Heat Loss (Thermolysis)
 Radiation
 Conduction
 Convection
 Evaporation
 Perspiration
 Respiration
 Loss through urine & feces

11. Role of Skin

12. Heat Exchange in the Skin

13. Vasoconstriction and
Vasodilatation

14. Thermoregulation
 Temperature is regulated by nervous
feedback mechanisms
 Thermoregulatory center located in the
Hypothalamus
 Thermoregulatory regulatory responses
include
Autonomic
Somatic
Endocrine
Behavioural changes

15. 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

16. 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

18. Thermoregulatory regulatory responses
 Activated by Exposure to Cold
1. Shivering
2. Increase voluntary activity
3. Increase TSH secretion
4. Increase Catecholamines
5. Vasoconstriction
6. Horripilation
7. Curling up

19. Thermoregulatory regulatory responses
 Activated by Exposure to Heat
1. Vasodilatation
2. Sweating
3. Increase in Respiration
4. Anorexia
5. Apathy
6. Decrease TSH secretion

20. 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

21. 1-A major source of heat
production in infants is
A. Increased muscular activity
B. Brown fat
C. Increased sympathetic activity
D. Specific dynamic action of food

22. 2-At normal room temperature
most body heat loss is by-
A. Convention
B. Conduction
C. Radiation
D. Sweating

23. 3-Constituents of secreted sweat are similar
to plasma except for
A. Proteins
B. Chloride
C. Bicarbonate
D. Potassium

24. 4-The only available mechanism of heat transfer
when the environmental temperature is greater than
the body temperature is
A. Radiation
B. Conduction
C. Convection
D. Evaporation

25. 5-Cause of thermogenesis in the
body is
A. Skeletal muscle relaxation
B. Assimilation of food
C. Decreased cardiac metabolism
D. Hypothyroidism

26. 6-A major factor resulting in increase
in body temperature during exercise
is-
A. Heat dissipating mechanisms
inefficient
B. Enormous thermogenesis
C. Vasoconstriction on non-working
muscles
D. Resetting of thermostat

27. 7-Site which reflects the true
value of core temperature
A. Oesophagus and rectum
B. Tympanic membrane
C. Vagina
D. All of the above

28. 8-BMR is dependent on
A. Body weight
B. Surface area
C. Amount of lean body mass
D. Height

29. 9-One feels hotter on a humid day
because-
A. Rate of sweating increases
B. Surrounding temperature is more
C. Heat loss by the body via process of
radiation decreases
D. Rate of evaporation of water from
body decreases

30. 10-A major factor resulting in increase
in body temperature during exercise
is-
A. Heat dissipating mechanisms
inefficient
B. Enormous thermogenesis
C. Vasoconstriction on non-working
muscles
D. Resetting of thermostat

32. Temperature Regulation
Dr Dileep Verma
Associate Professor
Deptt of Physiology
KGMU

33. Lecture-2 :Topics
 Life in Hot environment
-Effect of acute heat
 Thermoregulatory responses
 Heat syndrome
-Heat cramps
-Heat exhaustion
-Heat stroke

34. Contd…
 Life in cold environment
-effect of acute & long term
cold exposure on body
 Applied
-Hypothermia
-Harmful effects of extreme
cold

35. Learning Objectives
 Effect of Hot & Cold environment on
the body.
 Thermo-receptors
 Regulation of Body Temperature

36. 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%

37. Contd----
Effects of acute heat -
Effects of acute exposure to heat
are divided into-
a) Thermoregulatory responses
b) Other effects

38. Contd----
 Thermoregulatory regulatory responses
Vasodilatation
Sweating
Increase in Respiration
Anorexia
Apathy
Decrease TSH
secretion

39. Contd----
 Other effects of acute heat exposure on-
Cellular metabolism
Rate of respiration
Work of breathing
Pulse rate
Dehydration
Urinary volume

40. Contd----
Heat Syndromes- adverse
reaction to heat exposure
a) Heat Cramps
b) Heat Exhaustion
c) Heat Stoke

41. 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

42. Contd----
 Effect of acute cold exposure on body
Shivering
Increase voluntary
activity
Increase TSH secretion
Increase Catecholamines
Vasoconstriction
Horripilation
Curling up

43. Contd----
 Effect of long term cold
exposure
Metabolic Responses
Insulative Responses
Hypothermic Responses

44. Contd----
Hypothermia –Body temp below
the normal lower limit (<970F)
 Thermoregulatory responses
Greatly impaired at (<940F)
Lost at body temp(<850F)

45. Contd----
 Frostbite
Occurs at very low temp
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

46. Summary of Effector Mechanisms
in Temperature Regulation

47. 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

48. Core temperature of 260C leads to death
due to:
a) Brain damage
b) Respiratory insufficiency
c) Cardiac failure
d) All of the above

49. 2- Which area of hypothalamus
functions as thermostat?
A. Preoptic
B. Paraventricular
C. Dorso medial
D. Lateral

50. 3- Insensible water loss (perspiration) will
be absent if humidity is
A. 50%
B. 70%
C. 90%
D. 100%

51. 4- Pyrogens raises body temperature
by
A. Setting the thermostat to higher level
B. Releasing interleukins
C. Decreasing peripheral heat liberating
mechanism
D. Causing peripheral vasoconstriction

52. 5- Heat loss process of the body not
directly under physiological control is
A. Radiation from body
B. Conduction and convection to
surroundings
C. Vaporization of sweat
D. Warming of inspired air

53. 6- Fever is usually caused by
A. Interleukin-1
B. Substance- p
C. Endorphins
D. Encephalin

54. 7- During exposure to cold, body
temperature is raised by
A. Vasoconstriction in the skin
B. Horripilation
C. Thermogenesis
D. All of the above

55. 8- Profound hypothermic signs include
all except
A. Show breathing
B. Bradycardia
C. Hypotension
D. Hyperactivity

56. 9- Aspirin decreases the body
temperature by
A. Inhibiting interleukin-1
B. Inhibiting pyrogens release
C. Killing fever producing organisms
D. Inhibiting prostaglandin synthesis

57. 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 increases
D. All of the above