1. © 2010 McGraw-Hill Australia Thermoregulation Chapter 8 Homeostasis of body temperature and body fluids

2. © 2010 McGraw-Hill Australia Humans  In humans, body temperature is relatively constant  The usual body temperature is 36.8  C  In the body, heat gained = heat lost  This process is called thermoregulation, a term used to describe the processes which maintain the balance between heat production and heat loss

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4. Why Thermoregulate?  Chemical reactions occurring in cells are very heat-sensitive  Enzymes that control cellular activity are heat- sensitive

5. © 2010 McGraw-Hill Australia Rising Body Temperature Rising body temperature prompts heat loss in the body through:  blood flow to the skin  metabolic rate  behavioural responses  sweating

6. © 2010 McGraw-Hill Australia Blood Flow to Skin  Vasodilation:  in response to rising temperature, the body increases blood flow to the skin  is controlled by the autonomic nervous system  results in an increase in blood flow to the skin, allowing heat loss via radiation, conduction, convection and evaporation  prompts cooling of the blood that is flowing through the skin

7. © 2010 McGraw-Hill Australia Metabolic Rate  The metabolic rate changes through a reduction in the secretion of thyroxine  This results in a decrease in metabolic rate  The decrease in metabolic rate causes less heat to be produced in the body

8. © 2010 McGraw-Hill Australia Behavioural Responses We change our behavioural responses by:  staying still (decreasing activity)  staying in the shade  air conditioning  wearing less clothing

9. © 2010 McGraw-Hill Australia Sweat  Sweat is controlled by the sympathetic nervous system  It is secreted from sweat glands to skin  Sweat contains sodium chloride, urea, lactic acid and potassium ions  Sweat cools by evaporating from the body  Sweat doesn’t work in a humid environment  Environmental temperature > body temp for sweating to be effective

10. © 2010 McGraw-Hill Australia Rising Body Temperature

11. © 2010 McGraw-Hill Australia Falling Body Temperature Falling body temperature prompts:  changes in blood flow to the skin  changes in metabolic rate  shivering  behavioural responses

12. © 2010 McGraw-Hill Australia Blood Flow to Skin  In response to falling temperatures, the body restricts blood flow to the skin. This process is called vasoconstriction  Vasoconstriction:  is controlled by the sympathetic nervous system  decreases blood flow to the skin from internal organs, which decreases the transfer of heat from the internal body organs to the skin allows less heat to be lost from the body surface cools the skin

13. © 2010 McGraw-Hill Australia Falling Body Temperature – Skin

14. © 2010 McGraw-Hill Australia The Hypothalamus and the Adrenal Medulla  The hypothalamus stimulates the adrenal medulla via sympathetic nerves  The medulla secretes adrenaline and noradrenaline into the blood  This increases cellular metabolism, increasing heat production  This process helps maintain internal body temperature

15. © 2010 McGraw-Hill Australia The Hypothalamus and the Anterior Pituitary  The hypothalamus also stimulates the anterior lobe of the pituitary  The anterior pituitary secretes thyroid stimulating hormone (TSH)  TSH acts on the thyroid gland  The thyroid gland releases thyroxine into the blood  This increases metabolic rate, increasing body temperature

16. © 2010 McGraw-Hill Australia Shivering  Shivering is actually rhythmic muscle tremors occurring at a rate of around ten to twenty per second  The hypothalamus stimulates parts of the brain that increase skeletal muscle tone  This increases body heat production

17. © 2010 McGraw-Hill Australia Behavioural Responses We change our behavioural responses by:  huddling  curling into a ball  putting on more clothes  using a heating device

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19. Complete this negative feedback loop for rising body temperature.

20. © 2010 McGraw-Hill Australia Complete this negative feedback loop for falling body temperature.

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23. 1. In what ways do this model represent homeostasis

24. © 2010 McGraw-Hill Australia 2. For each of the following chemicals, indicate what activities will have an effect on levels in the body, and the effects of excesses or deficiencies on the body – at the whole body level and at the cellular level. Chemical Activities that affect levels Effects of excess Effects of Deficiency

25. © 2010 McGraw-Hill Australia 3. What are the normal operating ranges for the following in the human body? Temperature Blood pressure Glucose pH

26. © 2010 McGraw-Hill Australia 4. How will changes in pH affect the functioning of the cell? 5. How will changes in temperature affect the rates of reactions in the cell?

27. © 2010 McGraw-Hill Australia 6. State the name and location of the receptors for each of the factors listed in the table. FactorReceptorLocation Oxygen Carbon dioxide Body fluid concentration Glucose pH Temperature Blood pressure

28. © 2010 McGraw-Hill Australia