GCSE · Biology · AQA · Spec 8461

Control of body temperature/thermoregulation (biology only)

Step out into a freezing morning and within minutes you're shivering. You didn't decide to — a control centre in your brain noticed the change and flicked a switch.

Biology · Homeostasis

Rebuild your body's thermostat, then break it

2 stages are missing. Use the rest of the loop to work out which goes where.

Stage 1: Body temperature drifts away from normal
You might be getting too hot or too cold. Either way, something has to notice.
Stage 3: The thermoregulatory centre checks and decides
This centre is in the brain. It has its own receptors, sensitive to the temperature of the blood flowing through it, and it also receives the impulses from the skin. It coordinates the response.
Stage 5: Temperature heads back towards normal
The response pushes temperature the opposite way to the change. The centre is still watching — so the loop goes round again.

…and stage 5 leads back to stage 1.

Exam line: Name all three jobs in order: receptors detect the change, the thermoregulatory centre in the brain coordinates, effectors respond.

Biology · Two routes

Too hot or too cold? The body takes one route

The thermoregulatory centre has detected a change. Which way has body temperature gone?

Which way has body temperature moved?

2 possible responses.

On The thermoregulatory centre detects a change. 2 branches to choose from.

Pick a direction and see what the thermoregulatory centre switches on.

Watch out: Match the response to the direction: dilate when too hot, constrict when too cold.

Biology · Blood vessels

What are the blood vessels really doing?

You've been running and you're too hot. Your thermoregulatory centre switches on vasodilation.

Which is closest to what you think is happening to the blood vessels near your skin?

They move closer to the surface of the skin.They widen, so more blood flows through them near the skin.They narrow, which pushes the blood out to the skin faster.The body makes more blood so there's more to carry to the skin.

How sure are you?

I'm sureI think soI'm guessing

They move closer to the surface of the skin.

This is a common misconception

This is the most common picture of vasodilation — and it's wrong. Blood vessels can't travel through your skin; they stay exactly where they are. What changes is their width. Vessels near the skin dilate (widen), so more blood flows through them, and more energy reaches the skin to be transferred to the environment.

They widen, so more blood flows through them near the skin.

This matches the evidence

Spot on. That widening is vasodilation. The vessels haven't moved an inch — they've just opened up, so more blood, and so more energy, reaches the skin. When you're too cold, the opposite happens: they constrict (narrow), and less blood flows near the skin.

They narrow, which pushes the blood out to the skin faster.

This is a common misconception

Narrowing is vasoconstriction, and it's the too-cold response, not the too-hot one. Narrower vessels let less blood through near the skin, so less energy reaches the skin — which is what you want when you're cold, and the opposite of what you want now.

The body makes more blood so there's more to carry to the skin.

This is a common misconception

Vasodilation isn't about making blood. It changes where your blood flows: wider vessels near the skin let more of the blood you already have pass close to the surface.

Blood vessels don't move. They dilate (widen) or constrict (narrow), and that changes how much blood — and so how much energy — reaches the skin.

Exam line: Write 'the blood vessels dilate' or 'the blood vessels constrict'. Never write that they move.

Cooling down

Reason it through

Why do vasodilation and sweating bring your body temperature down?

Link 1 of 4

First link · your turn

The vessels near the skin have dilated. What changes about the blood in your skin?

Locked — reveal the link above first

Higher

Biology · Explain it in context

Write it, then mark it: a freezing bus stop

Ali is waiting at a bus stop on a freezing winter morning. His body temperature starts to fall. Explain how his body detects this change and responds to raise his body temperature back towards normal. [5 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

The thermoregulatory centre (in the brain) detects the fall in blood temperature, or skin temperature receptors send impulses to the thermoregulatory centre (1 mark)
Blood vessels supplying the skin constrict (vasoconstriction) (1 mark)
So less blood flows near the skin surface and less energy is transferred from the skin to the environment (1 mark)
Sweating stops, so less energy is transferred from the skin by sweat evaporating (1 mark)
Skeletal muscles contract (shivering) (1 mark)
Muscle contraction needs respiration, which releases energy that warms the body (1 mark)

Model answer

Receptors in Ali's thermoregulatory centre detect that his blood temperature has fallen, and receptors in his skin send nervous impulses to the centre. The centre coordinates a response. The blood vessels supplying his skin constrict, so less blood flows near the surface and less energy is transferred from his skin to the cold air. His sweating stops, so less energy is transferred from his skin by sweat evaporating. His skeletal muscles contract — he shivers — and the respiration needed for that muscle contraction releases energy, which warms his body.

Too cold: cut the energy leaving through the skin (vasoconstriction, no sweat) and release more inside (shivering). That pairing is the whole explanation.

Exam line: Pair every response with its effect: 'vasoconstriction, so less blood flows near the skin, so less energy is transferred to the environment.'

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Your brain runs a thermostat: it checks, it decides, it switches something on — and then it checks again.

What you need to know

Body temperature is monitored and controlled by the thermoregulatory centre in the brain.
The thermoregulatory centre contains receptors sensitive to the temperature of the blood.
The skin contains temperature receptors that send nervous impulses to the thermoregulatory centre.
Too hot: blood vessels dilate (vasodilation) and sweat glands produce sweat.
Too cold: blood vessels constrict (vasoconstriction), sweating stops and skeletal muscles contract (shiver).

The big picture

Body temperature is monitored and controlled by the thermoregulatory centre in the brain. It has its own receptors that sense the temperature of the blood, and temperature receptors in the skin send it nervous impulses. If the body is too hot, blood vessels dilate and sweat is produced, and both transfer energy from the skin to the environment. If the body is too cold, blood vessels constrict, sweating stops and skeletal muscles contract (shiver). Each response changes the very temperature the centre is watching, so it keeps checking — a loop, not a one-off.

Key points

1Temperature control is a loop: receptors detect a change, the thermoregulatory centre coordinates, effectors respond, and the new temperature is monitored again.

2Vasodilation and sweating both transfer energy from the skin to the environment, which lowers body temperature.

3Blood vessels never move towards or away from the skin — they widen or narrow, changing how much blood flows near the surface.

4Vasoconstriction means less blood flows near the skin, so less energy is transferred to the environment.

5Shivering is skeletal muscle contraction; the respiration it needs releases energy that warms the body.

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Worked example

Problem

Priya lowers herself into a very hot bath. Describe how her thermoregulatory centre finds out that her body is warming up.

⚠ Watch out

Getting the direction the wrong way round. Too HOT: vessels dilate and sweat is produced. Too COLD: vessels constrict, sweating stops and you shiver. Quick check: every response pushes temperature back the opposite way to the change.

🧠

Memory hook

Hot? Open up and sweat it out. Cold? Clamp down and shake. (Open up = vasodilation, clamp down = vasoconstriction, shake = shivering.)

✓

Check yourself

Cover the page and draw the loop from memory: detect, coordinate, respond, check again. Then add both routes — every response for too hot, and every response for too cold.

Flashcards

(14)

Where is body temperature monitored and controlled?

By the thermoregulatory centre in the brain.

What do the receptors in the thermoregulatory centre detect?

The temperature of the blood.

Which receptors keep the brain informed about the temperature at the body's surface?

Temperature receptors in the skin — they send nervous impulses to the thermoregulatory centre.

What is vasodilation, and when does it happen?

Blood vessels near the skin widening (dilating). It happens when body temperature is too high.

What is vasoconstriction, and when does it happen?

Blood vessels near the skin narrowing (constricting). It happens when body temperature is too low.

What do the sweat glands do when you are too hot?

Produce sweat.

How does sweating help to lower body temperature?

Sweat evaporates using energy from the skin, so energy is transferred from the skin to the environment.

How does vasodilation help to lower body temperature?

More blood flows through the skin, so more energy is transferred from the skin to the environment.

What three responses happen when body temperature is too low?

Vasoconstriction, sweating stops, and skeletal muscles contract (shivering).

What is shivering?

Skeletal muscles contracting — a response to body temperature being too low.

How does shivering help to raise body temperature?

Muscle contraction needs respiration, which releases energy that warms the body.

How does vasoconstriction help to keep the body warm?

Less blood flows near the skin, so less energy is transferred from the skin to the environment.

Do blood vessels move towards the skin when you're hot?

No. They stay put and change width: they dilate when you're hot and constrict when you're cold.

Why is temperature control a loop and not a one-way chain?

The response changes body temperature, and the thermoregulatory centre keeps monitoring that new temperature.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Rebuild your body's thermostat, then break it

Too hot or too cold? The body takes one route

What are the blood vessels really doing?

Write it, then mark it: a freezing bus stop

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