1. Contents What is Energy Used For? Processes that use energy
Contracting muscles
Building large molecules
Thermoregulation
Active transport
Summary quiz

2. Thermoregulation
The conditions outside your body are constantly changing.
One minute they can be hot, the next cold.
Despite these changes, your body must be kept at a constant temperature of…
37oC
The body needs to remain at 37oC is because this is the temperature at which our enzymes work most effectively.

3. Temperature and enzymes
Enzymes are temperature-sensitive chemicals that control many of the chemical reactions in the body.
How are enzymes are affected when body temperature changes?
hotter
colder
37oC
Enzymes work slowly and the body is suffering.
Enzymes work most effectively and body is fine.
Enzymes are heat-damaged and body can become ill.

4. Sensing body temperature
Body temperature is controlled by a region of the brain.
As blood flows around the body,
it passes through the thermoregulatory centre in the brain.
The brain senses body temperature by sensing the temperature of the blood.
rest of the body
Once the brain knows what the body temperature is, it can act to keep it steady.
How does the body react to hot and cold temperatures?

5. Feeling the heat When you feel too hot, how does your body react?
You sweat, which helps to cool you down.
Another cooling effect is that blood vessels in the skin expand.
This means that more blood gets near the surface of the skin, which is why some people go red when they are too hot!
The expansion of blood vessels uses some of the energy released by respiration.
How do blood vessels use this energy?

6. How do blood vessels use energy?
An artery wall is made of a thick inner layer of muscle.
outer wall
blood
muscle cells
The muscle cells are able to contract and relax using energy from respiration.
How does the contraction and relaxation of these muscles affect the blood flow through this blood vessel?

7. Blood vessels and blood flow
If the muscle lining a blood vessel contracts, the blood vessel becomes narrower and blood flow is constricted.
blood flow
constricted
If the muscle lining a blood vessel relaxes, the blood vessel becomes wider and the blood flow increases.
blood flow
increased

8. Blood vessels in the skin
How do blood vessels affect blood flow in the skin?
blood vessels
direction of
blood flow
skin surface
The brain can cause the contraction and relaxation of the muscles within the walls of these blood vessels.
This means that blood can be forced to take different routes through the blood vessels in the skin.
What happens to blood flow when the body is too hot?

9. Increasing blood flow to the skin
When the brain senses that the body is too hot, it acts to redirect the blood flow towards the surface of the skin.
blood vessel widens
blood vessel constricts
increased blood flow
to the surface
of the skin
The contraction and relaxation of these blood vessels forces more blood to flow within the surface of the skin.
Energy from respiration is used to power the contraction of the muscle cells that allows this redirection to happen.
How does this help to increase heat loss from the body?

10. Increasing heat loss from the skin
When blood flows to the surface of the skin, it passes near the air surrounding the body.
This air is much cooler than the temperature of the blood.
blood
skin
air
heat
The heat within the blood escapes to the cool air.
This causes body temperature to drop and you feel cooler.