What is homeostasis, and how does the body keep its temperature constant in hot and cold conditions?
Homeostasis as the maintenance of a constant internal environment, the role of the thermoregulatory centre and skin receptors, and the mechanisms of temperature regulation including sweating, shivering, vasodilation and vasoconstriction.
A focused answer to the WJEC GCSE Biology section 2.5 topic on homeostasis and temperature regulation, covering homeostasis as maintaining a constant internal environment, the thermoregulatory centre, skin and brain receptors, and the roles of sweating, shivering, vasodilation, vasoconstriction and hair erection.
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What this dot point is asking
WJEC wants you to define homeostasis, know that body temperature is monitored by the thermoregulatory centre and by receptors, and explain how sweating, shivering, vasodilation, vasoconstriction and hair erection keep the body temperature constant.
What is homeostasis
Homeostasis is the maintenance of a constant internal environment inside the body, despite changes outside. Examples that are controlled include body temperature, blood glucose concentration and water level.
A steady internal environment matters because enzymes and cells work best within a narrow range of temperature and conditions. If the body temperature rises too high, enzymes can be denatured and stop working; if it falls too low, reactions slow down too much. Keeping the temperature near 37 degrees Celsius keeps the body's chemistry working properly.
Homeostasis works by negative feedback: when a condition moves away from its normal level, the body triggers a response that brings it back. A rise in temperature triggers cooling; a fall triggers warming. The same idea controls blood glucose and water balance elsewhere in this module.
Detecting temperature change
Body temperature is monitored and controlled by the thermoregulatory centre in the brain. It receives information from:
- Receptors in the brain, which detect the temperature of the blood flowing through it.
- Receptors in the skin, which detect the temperature of the surroundings.
If the temperature moves away from normal (about 37 degrees Celsius), the thermoregulatory centre triggers responses in the skin and muscles to correct it.
Cooling down when too hot
When the body is too hot, it increases heat loss:
- Sweating: sweat glands release more sweat onto the skin. As the sweat evaporates it takes heat energy from the body, cooling it.
- Vasodilation: the small blood vessels supplying the skin capillaries widen, so more blood flows close to the surface and more heat is lost by radiation.
Warming up when too cold
When the body is too cold, it reduces heat loss and generates heat:
- Vasoconstriction: the small blood vessels supplying the skin capillaries narrow, so less blood flows near the surface and less heat is lost.
- Shivering: the muscles contract and relax rapidly, and this respiration releases heat.
- Hairs stand up: tiny muscles pull the body hairs upright, trapping a layer of insulating air. Sweating also stops.
These responses act together. Reducing heat loss (vasoconstriction, hairs trapping air, less sweating) and generating heat (shivering) both raise the temperature back towards normal.
Comparing the responses
It helps to set the hot and cold responses side by side, because exam questions often ask you to contrast them.
| Condition | Skin blood vessels | Sweating | Muscles | Hairs |
|---|---|---|---|---|
| Too hot | Vasodilation (widen) | More sweat | Relaxed | Lie flat |
| Too cold | Vasoconstriction (narrow) | Less sweat | Shiver | Stand up |
In every case the body is doing the opposite thing to push the temperature back to normal, which is why it is described as negative feedback.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksExplain how the body reduces its temperature when a person becomes too hot.Show worked answer →
A 4-mark explain question on cooling.
When the body is too hot, the thermoregulatory centre in the brain detects the rise and triggers responses in the skin. Sweat glands release more sweat, and as it evaporates it takes heat from the skin. The blood vessels supplying the skin capillaries widen (vasodilation), so more blood flows near the surface and more heat is lost by radiation. Together these lower the body temperature back to normal.
Markers reward: thermoregulatory centre detects the rise; more sweating, sweat evaporates and removes heat; vasodilation brings blood to the surface so more heat is lost. Saying the blood vessels "move to the surface" is wrong; they widen.
WJEC style3 marksDescribe two ways the body responds when it becomes too cold.Show worked answer →
A 3-mark describe question on warming.
When the body is too cold, the blood vessels supplying the skin narrow (vasoconstriction), so less blood flows near the surface and less heat is lost. The muscles also contract and relax rapidly (shivering), which releases heat from respiration. Hairs may also stand up to trap an insulating layer of air.
Markers reward any two of: vasoconstriction reducing blood flow to the skin; shivering releasing heat; hairs standing up to trap air; less sweating. Confusing vasoconstriction with vasodilation loses the mark.
Related dot points
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Sources & how we know this
- WJEC GCSE Biology specification (from 2016) — WJEC (2016)