GCSE · Biology · Edexcel · Spec 1BI0

Thermoregulation – shivering, vasoconstriction, vasodilation

You never decide to shiver, and you never tell your blood vessels to change size. So who runs your temperature? Follow one message to find out.

From a change in temperature to a response

Step through the pathway in order. Every temperature change takes the same route.

Shivering

Reason it through

Why does shivering warm you up?

Link 1 of 4

First link · your turn

Body temperature falls. What do the muscles (effectors) do when the instruction arrives along the motor neurons?

Locked — reveal the link above first

Which idea is yours?

Do you decide? And what do the vessel muscles actually do?

It's a freezing morning. Your body is shivering, your blood vessels near the skin are changing size, and you haven't asked for any of it.

Which is closest to what you think right now?

I choose to shiver, and I could choose to switch my sweating on or off.To make a blood vessel wider, the muscles around it contract and pull it open.When I'm cold, my vessels widen so more blood reaches my skin and keeps me warm.These responses are automatic. The muscles in the arteriole wall contract to narrow the vessels and relax to widen them.

How sure are you?

I'm sureI think soI'm guessing

I choose to shiver, and I could choose to switch my sweating on or off.

This is a common misconception

Not quite. These responses are autonomic: they happen without conscious control. The receptors, the thermoregulatory centre and the effectors do it all without you deciding anything.

To make a blood vessel wider, the muscles around it contract and pull it open.

This is a common misconception

Easy mistake, but it's backwards. When the muscles in the arteriole wall contract, the vessel narrows (vasoconstriction). To widen it, they relax (vasodilation).

When I'm cold, my vessels widen so more blood reaches my skin and keeps me warm.

This is a common misconception

That swaps the pair. Too cold means vasoconstriction: narrower vessels, less blood at the surface, and less heat radiated away. More blood at the surface is vasodilation, and that loses heat faster.

These responses are automatic. The muscles in the arteriole wall contract to narrow the vessels and relax to widen them.

This matches the evidence

Yes. Autonomic, and contract = narrower (vasoconstriction), relax = wider (vasodilation).

Nobody decides. Contract = narrow = vasoconstriction (too cold). Relax = wide = vasodilation (too hot).

Your turn to write

Explain the response to getting too hot

Explain how the body responds when its temperature rises too high. [4 marks]

Your answer

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

The mark scheme

Temperature receptors (in the skin or the hypothalamus) detect the increase. (1 mark)
The thermoregulatory centre, in the hypothalamus, coordinates the response. (1 mark)
Vasodilation: the muscles around the blood vessels relax, increasing blood flow to the surface of the skin so more heat is radiated. (1 mark)
Sweat glands secrete sweat, which removes heat by evaporation. (1 mark)

Model answer

Temperature receptors in the skin or the hypothalamus detect the increase. The thermoregulatory centre in the hypothalamus coordinates the response. Vasodilation happens: the muscles around the blood vessels relax, so more blood flows to the surface of the skin and more heat is radiated. Sweat glands also secrete sweat, which removes heat by evaporation.

Hot answer: receptors detect, the centre coordinates, vasodilation lets more heat be radiated, sweat removes heat by evaporation.

Exam line: A full answer joins the pathway to the effectors: detect, coordinate, then say what each effector does and why that loses heat.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Your body runs its own thermostat, and it never asks your permission.

What you need to know

Temperature receptors in your skin detect changes in the external temperature.
Receptors in the hypothalamus of your brain detect changes in blood temperature.
Receptors send nerve impulses along sensory neurons to the thermoregulatory centre, which is located within the hypothalamus.
The centre coordinates a response, sending impulses along motor neurons to effectors: muscles and glands.
Have a goSam says, 'My skin receptors send their message straight to my muscles.' Where does the message have to stop off first?
At the thermoregulatory centre, in the hypothalamus.
The route is receptor, sensory neuron, thermoregulatory centre, motor neuron, effector. The centre coordinates the response before anything reaches the muscles.
When body temperature decreases, muscles contract and relax repeatedly and very rapidly. That is shivering.
Shivering generates heat through cellular respiration, an exothermic process, so it warms the body.
Have a goSam, now confidently wrong, says shivering warms you because the muscles rub together. Which process in the cells actually generates the heat?
Cellular respiration, an exothermic process.
Shivering generates heat through cellular respiration, and an exothermic process gives out heat, which is why it warms the body.
Too cold: muscles in the arteriole wall contract (vasoconstriction), so less blood reaches the skin surface and heat is kept in the central core.
Too hot: those muscles relax (vasodilation), so more blood reaches the surface, more heat is radiated and heat is lost faster.
Have a goYou're overheating. Is it vasoconstriction or vasodilation in the vessels near your skin, and are the vessel-wall muscles contracting or relaxing?
Vasodilation, with the muscles relaxing.
Too hot means the muscles relax and the vessels widen. Contracting muscles would narrow them, which is vasoconstriction.
Sweat glands secrete sweat when you are too hot, removing heat by evaporation. When you are too cold, they stop.
All of these responses are autonomic (no conscious control) and antagonistic (they work against each other to keep temperature in a narrow range).

The big picture

Temperature receptors in the skin and the hypothalamus detect a change. Sensory neurons carry the message to the thermoregulatory centre, which coordinates a response and sends impulses along motor neurons to effectors (muscles and glands). Shivering, vasoconstriction, vasodilation and sweating are autonomic, antagonistic responses that keep body temperature within a narrow range.

Key points

1Receptors, sensory neurons, thermoregulatory centre, motor neurons, effectors: the same pathway every time.

2Too cold: shivering and vasoconstriction, and the sweat glands stop. Too hot: vasodilation and sweating.

3Vasoconstriction is the narrowing of blood vessels; vasodilation is the widening of blood vessels.

4The responses are autonomic and antagonistic.

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Worked example

Problem

Someone steps from a warm building into freezing air. Describe what the muscles around their blood vessels do, and explain how that helps them.

⚠ Watch out

Mixing up the muscle action. Contracting muscles in the arteriole wall make the vessel narrower, not wider. The widening (vasodilation) comes from the muscles relaxing.

🧠

Memory hook

Constriction = Cold = Contract = Closer together (narrower). Cold squeezes the vessels narrow; heat lets them relax wide.

✓

Check yourself

Without looking: put the five parts of the pathway in order, from receptors to effectors. Then name the hot-weather opposite of vasoconstriction.

Flashcards

(12)

Where are the temperature receptors, and what does each set detect?

In the skin, detecting external temperature. In the hypothalamus, detecting blood temperature.

What is the thermoregulatory centre?

The coordination centre inside the hypothalamus that regulates the body's response to changes in internal body temperature.

Which neurons carry impulses TO the thermoregulatory centre, and which carry them AWAY?

Sensory neurons carry impulses to the centre. Motor neurons carry impulses from the centre to the effectors.

What are the effectors in temperature control?

Muscles and glands.

What is shivering?

Muscles contracting and relaxing repeatedly and very rapidly when body temperature decreases.

Why does shivering warm the body?

It generates heat through cellular respiration, which is an exothermic process.

Define vasoconstriction.

The narrowing of blood vessels, reducing blood flow through them.

Define vasodilation.

The widening of blood vessels, increasing blood flow through them.

How does vasodilation help when body temperature is too high?

It increases blood flow to the skin surface, so more heat can be radiated and heat is lost faster.

How does sweating cool the body, and what do the sweat glands do when it is too cold?

Sweat removes heat through evaporation. When body temperature goes too low, the sweat glands stop secreting sweat.

What does 'autonomic' mean for these responses?

They happen without conscious control.

What does 'antagonistic' mean for these responses?

They work against each other in order to keep body temperature within a constant narrow range.

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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Thermoregulation – shivering, vasoconstriction, vasodilation

Which response does what?

Do you decide? And what do the vessel muscles actually do?

Explain the response to getting too hot

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