Temperature Control
Higher tier: how your body holds 37 °C — the brain's thermostat, and the sweating, shivering and blood-vessel tricks that keep you steady.
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Temperature Control 🌡️
*(Higher tier.)* Whether you're in a heatwave or a blizzard, your core body temperature barely moves from about **37 °C** — the temperature your **enzymes** work best at. How does your body hold it so steady? A thermostat in your brain, and some clever tricks in your skin.
The brain's thermostat 🧠
Body temperature is monitored and controlled by the **thermoregulatory centre** in the **brain**. It contains receptors that are sensitive to the temperature of the **blood** flowing through it. The **skin** also has temperature receptors that send impulses to the centre. If the temperature drifts from 37 °C, the centre triggers a response to correct it.
Where's the thermostat?
Where is your body temperature monitored and controlled?
- The thermoregulatory centre in the brain
- Only in the skin
- In the heart
- In the liver
Too hot: lose the heat 🔥
When you get **too hot**, the body works to **lose** heat: • **Vasodilation** — the blood vessels supplying the skin capillaries **widen**, so more blood flows near the surface and more heat is lost. • **Sweating** — sweat glands release sweat; as it **evaporates** it takes heat energy from the skin, cooling you down.
Too cold: keep the heat ❄️
When you get **too cold**, the body works to **keep** heat: • **Vasoconstriction** — the skin blood vessels **narrow**, so less blood flows near the surface and less heat is lost. • **Shivering** — your muscles contract rapidly; this requires **respiration**, which releases heat and warms you.
Hot day, cold night
An interactive activity.
How each works
- Vasodilation
- Vasoconstriction
- Sweating
- Shivering
- Skin vessels widen, so more heat is lost
- Skin vessels narrow, so less heat is lost
- Sweat evaporates, taking heat from the skin
- Muscles contract, and respiration releases heat
How heat escapes
In vasodilation, how is more heat lost from the skin?
- The skin blood vessels widen, so more blood flows near the surface and more heat radiates away
- The blood vessels move up to the skin surface
- The blood flows twice as fast
- The blood becomes thinner
Hot and cold
When too hot, skin blood vessels _____ and sweat glands release sweat; when too cold, the vessels _____ and you _____.
Why shiver?
When you are too cold, how does shivering help warm you up?
- The muscles contract rapidly, and the respiration this needs releases heat
- It pushes warm blood to the surface
- It makes you sweat to warm up
- It burns body fat directly for warmth
In the exam 🎓
Thermostat mastered. Grade-9 habits for thermoregulation (HT): • The **thermoregulatory centre** in the **brain** monitors blood temperature and corrects any drift from 37 °C. • **Too hot** → **vasodilation** + **sweating**; **too cold** → **vasoconstriction** + **shivering**. • Always give the **mechanism**: vessels **widen/narrow**, changing blood flow near the skin to increase/decrease heat loss — they do NOT move.