12.1 Controlling Body Temperature

A free GCSE Biology lesson for AQA (8461) from OBA School: how the thermoregulatory centre, sweating, blood vessels and shivering keep your core at about 37 °C. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Explain why core body temperature must be kept close to 37 °C
• Describe how the thermoregulatory centre and skin receptors monitor temperature
• Explain how sweating and vasodilation cool the body down
• Explain how vasoconstriction, shivering and less sweating warm the body up
• Use the idea of negative feedback to explain temperature control in a given context

Key words

• Homeostasis: Keeping internal conditions (such as temperature, water and blood glucose) within set limits, so cells work properly.
• Core temperature: The temperature deep inside the body. In humans it is about 37 °C.
• Thermo-regulatory centre: The part of the brain that monitors and controls body temperature. It has receptors that sense the temperature of the blood.
• Vasodilation: Widening of the blood vessels that supply the skin capillaries, so more blood flows near the skin surface.
• Vaso-constriction: Narrowing of the blood vessels that supply the skin capillaries, so less blood flows near the skin surface.
• Shivering: Rapid, automatic contraction and relaxation of skeletal muscles. Extra respiration releases energy that warms the body.
• Negative feedback: A change away from the normal level triggers a response that brings it back towards normal.

Why body temperature is controlled

Your cells rely on enzymes. Human enzymes work best at about 37 °C. Your body keeps its core temperature very close to this, even when the air around you is much hotter or colder.

• About 37 °C; What happens Normal. Enzymes work at their optimum rate.
• Above about 40 °C; What happens Heat stroke risk. Enzymes start to denature (the active site changes shape) and cells are damaged.
• Below about 35 °C; What happens Hypothermia. Enzyme-controlled reactions slow down, so cells cannot release enough energy.

Key fact: Temperature control is an example of homeostasis. It is automatic: you do not have to think about it.

Detecting a change in temperature

The thermoregulatory centre is in the brain (in a region called the hypothalamus). It contains receptors that are sensitive to the temperature of the blood flowing through it.

The skin also has temperature receptors. They send nerve impulses to the thermoregulatory centre, giving early warning about the temperature outside.

The thermoregulatory centre then sends nerve impulses to effectors: sweat glands, the blood vessels supplying the skin, and skeletal muscles.

Cooling down: sweating and vasodilation

• Sweating. Sweat glands release more sweat onto the skin. When the water in sweat evaporates, it transfers energy away from the skin, which cools the body.
• Vasodilation. The blood vessels that supply the skin capillaries widen. More blood flows through the capillaries close to the surface, so more energy is transferred to the surroundings by radiation.

Worked example: explain in a given context

After a hard game of football, Leah’s face looks red and her shirt is wet. Explain these changes.
Her muscles respired fast, so her core temperature rose. The thermoregulatory centre detected this.
Red face: vessels supplying the skin capillaries widened (vasodilation), so more warm blood flowed near the surface and more energy was lost by radiation.
Wet shirt: sweat glands made more sweat; evaporation of the water transferred energy from the skin.

Answer: vasodilation and sweating both transfer energy away, lowering core temperature

Warming up: vasoconstriction, shivering and less sweat

• Vasoconstriction. The blood vessels that supply the skin capillaries narrow. Less blood flows near the surface, so less energy is lost. Skin can look pale.
• Shivering. Skeletal muscles contract and relax quickly. This needs more respiration, and respiration releases energy, some of which warms the blood.
• Less sweating. Sweat production falls, so less energy is lost by evaporation.

Exam tip: Blood vessels do not move up or down in the skin. They get wider or narrower, which changes how much blood flows near the surface.

Tiny muscles can also raise body hairs when you are cold ("goose bumps"). In furry mammals this traps a layer of insulating air, but in humans the effect is very small.

Using data about temperature control

Exam questions often give data about sweat loss or body temperature. Water lost in sweat can be estimated from a change in body mass, because 1 kg of sweat is roughly 1 litre of water.

Worked example: rate of sweat loss

A cyclist has a mass of 68.40 kg before a 90-minute ride and 67.32 kg afterwards. She drank nothing. Calculate her mean rate of mass loss in g per minute.
Mass lost = 68.40 − 67.32 = 1.08 kg = 1080 g
Rate = 1080 ÷ 90 = 12 g per minute

Answer: 12 g per minute (mostly water lost as sweat)

Key fact: On a humid day, sweat evaporates more slowly, so it cools you less. That is why hot, humid weather is more dangerous during exercise.

Common mistakes

• Saying blood vessels or capillaries "move closer to the skin". They widen (vasodilation) or narrow (vasoconstriction).
• Saying sweat cools you because it is cold. It is the evaporation of water from sweat that transfers energy away from the skin.
• Mixing up the two words: vasodilation helps you lose energy; vasoconstriction helps you keep it.
• Writing that shivering "makes heat" with no reason. Say that muscle contractions need more respiration, which releases energy.
• Forgetting the receptors in the thermoregulatory centre itself. It senses blood temperature directly; skin receptors send nerve impulses.

Revision questions

Try these, then check your answers below each one.

Question 1. Where are the receptors that detect the temperature of the blood? (Choose from: In the thermoregulatory centre in the brain, In the skin, In the pancreas, In the kidneys.)

Answer: In the thermoregulatory centre in the brain

Working: The thermoregulatory centre in the brain contains receptors sensitive to the temperature of the blood flowing through it. Skin receptors send nerve impulses about skin temperature.

Question 2. True or false? When you are cold, the blood vessels supplying your skin capillaries move deeper into the skin.

Answer: False

Working: False. Blood vessels do not move. They narrow (vasoconstriction), so less blood flows near the skin surface.

Question 3. During a race, Zara’s core temperature rises to 38.5 °C. Which pair of responses happens? (Choose from: Vasoconstriction and more sweating, Vasodilation and shivering, Vasoconstriction and shivering, Vasodilation and more sweating.)

Answer: Vasodilation and more sweating

Working: To cool down, vessels supplying skin capillaries widen (vasodilation) and sweat glands make more sweat. Vasoconstriction and shivering would warm her up.

Related lessons

• Previous lesson: 11.11 Required Practicals: Hormonal Coordination
• Next lesson: 12.2 Removing Waste Products
• In this chapter: 12.3 The Human Kidney
• In this chapter: 12.4 Dialysis – an Artificial Kidney
• In this chapter: 12.5 Kidney Transplants

Continue in the full course

This lesson is section 12.1 (AGCBH1201) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.