🧠 In the brain
The thermoregulatory centre contains receptors that are sensitive to the temperature of the blood flowing through it. It reads your core temperature directly.
The Human Nervous System » Controlling Body Temperature
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.5.2.4 (Biology only)
- How the brain monitors and controls body temperature
- What happens in the body when it gets too hot
- What happens in the body when it gets too cold
- How to explain these changes in an exam question
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Unlock This CourseWhy body temperature is controlled
Your body works best at an internal temperature of about 37°C. This is the temperature at which your enzymes work at their best. Too hot or too cold and your cells cannot do their jobs properly. Controlling temperature is one example of homeostasis, which you met in Homeostasis and Control Systems.
Temperature control has receptors, a coordination centre and effectors. In this lesson you will see exactly which parts do each job.
Key terms:
- Thermoregulatory centre: the part of the brain that monitors and controls body temperature.
- Vasodilation: blood vessels near the skin surface widen (dilate).
- Vasoconstriction: blood vessels near the skin surface narrow (constrict).
- Shivering: rapid, small contractions of skeletal muscles.
The thermoregulatory centre and its receptors
Body temperature is monitored and controlled by the thermoregulatory centre in the brain. It is the coordination centre for temperature control. It gets information from two places:
✌ In the skin
The skin contains temperature receptors. They detect how hot or cold the surroundings are and send nervous impulses to the thermoregulatory centre.
When the centre detects that the temperature is too high or too low, it sends signals to effectors that bring it back towards normal. The effectors you need to know are the blood vessels, the sweat glands and the skeletal muscles.
When the body temperature is too high
If the body temperature rises above normal, two things happen:
- Vasodilation: the blood vessels in the skin dilate, so more blood flows close to the surface of the skin.
- Sweating: the sweat glands produce sweat, which is mostly water, onto the skin.
Both mechanisms cause a transfer of energy from the skin to the environment, which cools you down.
💧 Vasodilation
More warm blood near the surface means more energy is transferred from the skin to the cooler air around it. This is why your face looks red and flushed when you are hot.
☀ Sweating
Sweat on the skin evaporates. Evaporation takes energy from the skin, so the skin and the blood beneath it cool down.
When the body temperature is too low
If the body temperature falls below normal, the opposite changes happen:
- Vasoconstriction: the blood vessels in the skin constrict, so less blood flows near the surface and less energy is transferred to the surroundings.
- Sweating stops: no sweat is produced, so no energy is lost by evaporation.
- Shivering: skeletal muscles contract rapidly. This needs energy from respiration, and some of that energy warms the body.
Common mistakes
Blood vessels do not move up and down towards the skin. They get wider (vasodilation) or narrower (vasoconstriction). Also, do not say that sweating "lets heat out through pores". It is the evaporation of the sweat that cools you.
Putting it together
This table sums up the whole response. Learn it so you can write it out from memory.
| Body temperature | Blood vessels in skin | Sweating | Shivering |
|---|---|---|---|
| Too high | Vasodilation | Sweat produced | No |
| Too low | Vasoconstriction | Sweating stops | Yes |
Each change is reversed once the temperature returns to normal. This is what keeps the body temperature close to 37°C all the time.
Explaining in context
Higher tier only
You need to be able to explain how these mechanisms lower or raise body temperature in a given context. A good explanation names the change, then says what it does to energy transfer, then says what that does to body temperature.
Worked example
Question: A runner has a high body temperature after a race. Explain how vasodilation helps to cool them.
Step 1: The blood vessels in the skin dilate. Step 2: More blood flows close to the skin surface. Step 3: More energy is transferred from the blood to the cooler surroundings. Step 4: The blood returning to the body is cooler, so body temperature falls.
Worked example
Question: A hiker is standing in cold wind. Explain how shivering helps to warm them.
Skeletal muscles contract quickly. The muscle cells respire to release the energy needed for this. Some of the energy is transferred as heat to the body, so body temperature rises.
Exam-style question
A student walks from a warm room into a cold playground.
(a) Name the part of the brain that monitors the student's body temperature. [1 mark]
(b) Describe two changes that happen in the student's body when the body temperature falls. [2 marks]
(c) Higher tier only: explain how one of these changes helps to raise the student's body temperature. [2 marks]
Model answer
(a) The thermoregulatory centre (1).
(b) Any two from: blood vessels in the skin constrict, or vasoconstriction (1); sweating stops (1); skeletal muscles contract or the student shivers (1).
(c) Shivering: the muscles contract rapidly and need energy from respiration (1). Some of this energy is transferred as heat to the body, which raises its temperature (1). Or vasoconstriction: less blood flows near the skin surface (1), so less energy is transferred to the surroundings (1).
Exam tip
For an "explain" question like part (c), give the change AND what it does to energy. Writing only "shivering warms you up" will not get both marks.