Temperature controlOxford AQA IGCSE Biology: Revision notes
Section 1
What monitors and controls body temperature?
Body temperature is monitored and controlled by the thermoregulatory centre in the brain. This centre contains receptors that are sensitive to the temperature of the blood flowing through the brain, so it constantly detects the core body temperature.
The thermoregulatory centre also receives information from temperature receptors in the skin, which send impulses along nerves reporting the temperature of the skin's surface. Combining information about core (blood) temperature and skin temperature allows the brain to make an accurate, fast response to keep the body at a stable temperature, around 37 °C, which is the temperature at which enzymes in the body work best.
Section 2
What happens in the body when core temperature is too high?
If the thermoregulatory centre detects that the core body temperature is too high, it triggers responses that increase heat loss:
- Blood vessels supplying the skin capillaries dilate (widen) — this is called vasodilation. More blood flows close to the surface of the skin, so more energy (heat) is transferred from the blood to the environment.
- Sweat glands release more sweat. As sweat evaporates from the skin surface, it transfers energy away from the body, cooling it down.
Because more water is lost as sweat when it is hot, more fluid must be taken in through food and drink to replace this loss and avoid dehydration.
Section 3
What happens in the body when core temperature is too low?
If the thermoregulatory centre detects that the core body temperature is too low, it triggers responses that reduce heat loss and generate more heat:
- Blood vessels supplying the skin capillaries constrict (narrow) — this is called vasoconstriction. Less blood flows close to the skin surface, so less energy is transferred from the blood to the environment, conserving heat.
- Muscles may 'shiver'. Shivering is rapid, repeated muscle contraction. Muscle contraction requires respiration, and respiration transfers some energy that warms the body.
Unlike sweating, which is switched off (not reversed) when the body is cold, vasoconstriction and shivering are active responses that generate or conserve heat.
Section 4
How do vasodilation and vasoconstriction change blood flow to the skin?
The same blood vessels supplying skin capillaries can widen or narrow depending on the signals sent by the thermoregulatory centre.
| Condition | Blood vessel response | Blood flow to skin capillaries | Effect on heat loss |
|---|---|---|---|
| Body too hot | Dilate (vasodilation) | Increases | More heat lost to environment |
| Body too cold | Constrict (vasoconstriction) | Decreases | Less heat lost to environment |
This is why skin can look flushed and feel warm when a person is overheating, and pale and feel cool when a person is cold — it reflects how much blood is flowing near the skin surface.
Section 5
Why is temperature control important for the body's enzymes?
Enzymes in the body work best within a narrow range of temperatures, close to normal body temperature (37 °C). If body temperature rises too high, enzymes can become denatured — their shape changes permanently and they stop working. If body temperature falls too low, enzyme-controlled reactions (including respiration) slow down, reducing the energy available for normal body processes.
Because the thermoregulatory centre constantly monitors blood and skin temperature and triggers responses (vasodilation/vasoconstriction, sweating, shivering) to correct any deviation, the body maintains a temperature that keeps enzyme activity — and therefore all the chemical reactions of life — working efficiently.
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