1. Thermoregulation
Objective:
* Identify the different structures on the diagram of a skin
** Describe how body temperature is kept constant
*** Explain thermoregulation in terms ofvasodilation and vasoconstriction

2. Name the largest organ of the body.
What are its functions?
Protects body from damage
Stops pathogen from entering
Prevents too much water loss
Detects changes in temperature
Detects pressure (touch) and pain
Loses heat by conduction, convection and radiation

3. the hypothalamus acts like the programmer in the central heating system.
messages from the brain go to parts of the body that can have an effect - the effectors.
temperature sensors in the skin are like the thermostats in the heating system.
a ‘message’ from temperature sensors in the skin

5. Keeping constant temper ature
To keep warm:
Shivering – uses energy
Releasing energy from food
Vasoconstriction
Exercising
To keep cool:
Sweating reduces temperature
Removing energy from body
Vasodilation
Sit or lay down
Controlled by the hypothalamus

6. body temperature normal body temperature falls
hair stands up and a
goose bump appears
hair lies flat on the skin
the muscle is relaxed
the muscle contracts

7. Sweating Sweat is produced in sweat glands
Sweat on your skin evaporates and it takes heat energy from your body to turn the liquid to a gas. This cools you down.

8. Hypothalamus (of a sheep)

9. Skin based effectors

10. Skin based effectors

11. Effector Response Skin based effectors – responding to heat gain
Arterioles supplying skin capillaries
The muscles relax – this is known as vasodilation. The effect of this is to increases the blood flow to the surface of the skin causing increased heat loss by radiation.
Sweat glands
The glands secrete sweat onto the surface of the skin. The sweat is composed mainly of water, which evaporates from the skin surface. As water has a high latent heat of evaporation the evaporating sweat removes heat from the surface of the skin.
Hair erector muscles
The muscles relax – this lowers the hairs on the skin surface. The hairs do not trap air when laid flat so they allow heat to be removed more easily by convection.

12. Effector Response Skin based effectors – responding to heat loss
Arterioles supplying skin capillaries
The muscle contract – this is known as vasoconstriction. Blood flows through the shunt vessel as this is the path of least resistance. Less blood flows to the surface of the skin so there is less heat loss by radiation.
Sweat glands
The sweat glands stop producing sweat therefore stopping the heat loss of evaporating sweat.
Hair erector muscles
The muscle contract – this raises the hairs on the surface of the skin. The effect of this is to reduce airflow therefore reducing convection of heat from the skin.

14. Skin based effectors

15. Other effectors and responses
Another well-known response to a lowered core temperature is shivering. The effectors for this response are the body’s skeletal muscles which contract and relax involuntarily to generate heat.
A lowered core temperature also stimulates the release of the hormones adreneline and thyroxine from the adrenal and thyroid glands. Both these hormones increase the body’s metabolic rate again generating heat.

16. Shivering

17. Responding to vigorous exercise
·        stimulus is the increase in blood temperature
·        this is caused by exercise/increased respiration/muscle contraction
·       the increase blood temperature is detected by receptors in the hypothalamus
·       the hypothalamus also acts as the co-ordinator
·        the effectors are muscles of arterioles
·        and sweat glands
·        response to arteriole muscles stimulation is vasodilation
·        which causes increased blood flow to the skin capillaries
·        which causes increased heat loss by radiation
·        response to sweat gland stimulation is increased sweating
·        which causes increased heat loss by the latent heat of evaporation

18. Exam questions
1. All living organisms exist in changing external environments and many are able to control their internal environments.
(a) Explain how the body of a mammal may respond to a rise in the environmental temperature. (8marks)

19. Exam answers
Thermoreceptors in skin; nervous impulse; to hypothalamus; blood temperature monitored; heat loss centre involved; vasodilation / dilation of arterioles; more blood to skin surface; more heat lost by radiation; piloerector muscles relax; hairs flatten on skin surface; less insulation; sweating initiated / increased; panting / licking; evaporation removes latent heat;
thinner fur; migration; drop in metabolic rate / use less brown fat; accept long term changes such as less fat deposition; accept one behavioural process;
max. 8