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

2. 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

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

5. Rising Body Temperature
Rising body temperature prompts heat loss in the body through:
blood flow to the skin
metabolic rate
behavioural responses
sweating

6. 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. 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. Behavioural Responses
We change our behavioural responses by:
staying still (decreasing activity)
staying in the shade
air conditioning
wearing less clothing

9. 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. Rising Body Temperature

11. Falling Body Temperature
Falling body temperature prompts:
changes in blood flow to the skin
changes in metabolic rate
shivering
behavioural responses

12. 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. Falling Body Temperature – Skin

14. 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. 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. 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. Behavioural Responses
We change our behavioural responses by:
huddling
curling into a ball
putting on more clothes
using a heating device

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

20. Complete this negative feedback loop for falling body temperature.