Temperature Regulation

1. Temperature Regulation Dr DileepVerma 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. 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 Body Temperature Control System

18. Thermoregulatory regulatory responses Activated by Exposure to Cold Shivering Increase voluntary activity Increase TSH secretion Increase Catecholamines Vasoconstriction Horripilation Curling up

19. Thermoregulatory regulatory responses Activated by Exposure to Heat Vasodilatation Sweating Increase in Respiration Anorexia Apathy 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 Increased muscular activity Brown fat Increased sympathetic activity Specific dynamic action of food

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

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

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

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

26. 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

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

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

29. 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

30. 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

32. Temperature Regulation Dr DileepVerma 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 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

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

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

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