1. Higher Biology Metabolism and survival
Thermoregulation

2. Todays Plan Learning Intentions –
I can explain what factors can affect the metabolic rate of an organism.
I can explain the difference between a conformer and regulator.
I can explain how a conformer maintains its metabolic rate.
I can explain why conformers have a low metabolic niche.
I can explain the importance of certain behaviour responses in conformers.
I can explain how a regulator maintains its metabolic rate.
I can explain what homeostasis is and how it is maintained.

3. Control of body temperature by homeostasis
Examples
Ectotherm
Varies with that of the environment
Invertebrates, fish, amphibians, reptiles
Endotherm
Constant and independent of the environment
Birds, mammals
The hypothalamus has thermoreceptor cells that monitor body temperature by: the temperature of blood coming to the brain nerve messages from skin thermoreceptor nerve endings The thermoreceptors send messages along motor nerves to effectors which trigger corrective feedback mechanisms – which return the body temperature to normal

4. Ectotherms
Animal that cannot control its body temperature by physiological means – its temperature varies with that of the environment
reptiles
amphibians
fish

5. Endotherm
Animal that can control its body temperature by physiological means A high metabolic rate generates enough heat to maintain a relatively constant temperature despite temperature variations in the external environment
birds
mammals

6. Environmental temperature (oC)
Body temperature (oC) 40 30 20 10
Environmental temperature (oC)
ENDOTHERM
ECTOTHERM

7. Physiological homeostasis
Thermoregulation in mammals/humans is achieved using:
Receptors
Thermoreceptors in hypothalamus
Control centre
Hypothalamus
Message
Nerve Impulses
Effectors
Skin and muscles
The hypothalamus plays a vital part in temperature regulation. It acts as a thermostat and responds to nerve impulses it receives from the hot and cold
receptors in the skin.
In addition the hypothalamus itself contains thermoreceptors that are responsive to changes in blood temperature

8. Thermoregulation Hypothalamus containing central thermoreceptors
Change in temperature
of blood in carotid artery
Nerve impulses from skin thermoreceptors
Nerve impulses sent to effectors
Hair erector muscles
Sweat glands
Skin arterioles
Skeletal muscles

9. Thermoregulation Release sweat which evaporates using heat from body
Skin arterioles
Dilate and increase blood flow to skin capillaries
Structure
Action
Effect
sweat glands
Hair erector muscles
skeletal muscles
Release sweat which evaporates using heat from body
Contract and raise hairs to trap layer of warm air next to skin
Involuntary contraction = shivering, which generates heat
Constrict and decrease blood flow to skin
capillaries
Heat loss
Heat generated
Heat retained

10. Vasoconstriction
When skin arterioles constrict this is called vasoconstriction.
Small arterioles just below the skin contract, vasoconstriction, less blood flows closer to the skin surface and less heat is lost by radiation
Hot blood
Vasoconstricton arteriole contracts
Less heat lost through radiation
Shunt vessel opens
Skin

11. Vasodilation
When skin arterioles dilate (open out) this is called vasodilation.
Small arterioles just below the skin expand, vasodilation, more blood flows closer to the skin surface and heat is lost by radiation cooling the body
Hot blood
Vasodilation arteriole expands
More heat lost through radiation
Shunt vessel closed
Skin

12. The action of hair erector muscles – too hot
Flattening of body hair next to the skin
Tiny erector muscles attached to the hair follicles are relaxed
Erector muscles relaxed
Skin
Hair lies close to skin thin layer of trapped air

13. The action of hair erector muscles – too cold
Raising of body hair next to the skin
Tiny erector muscles attached to the hair follicles contract and pull hair up
Erector muscles contracted
Skin
Hair lies raised above skin thick layer of trapped air insulating the body

14. Thermoreceptors in hypothalamus
Sequence of events
Overheating
Overcooling
Activity or stimulus
Strenuous exercise
Hypothermia
Body temperature
Rises
Falls
Thermoreceptors in hypothalamus
Detect rise
Detect fall
Message to skin
Vasodilation
Increase sweating rate
Vasoconstriction
Contract hair erectors
Effect
Increases heat loss
Decreases heat loss
Message to muscles
Shivering (rapid contraction)
Generates heat
Result
Body temperature falls
Body temperature rises

15. Can I..
Explain what factors can affect the metabolic rate of an organism.
Explain the difference between a conformer and regulator.
Explain how a conformer maintains its metabolic rate.
Explain why conformers have a low metabolic niche.
Explain the importance of certain behaviour responses in conformers.
Explain how a regulator maintains its metabolic rate.
Explain what homeostasis is and how it is maintained.