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 are in a heatwave or a blizzard, your core body temperature barely moves from about **37 °C**: the temperature your **enzymes** work best at. It is held there by the **thermoregulatory centre** in the **brain**, which contains receptors 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.
Order the feedback loop
Your core temperature has risen above 37 °C. Put the stages of the correction into the order they happen.
- Receptors detect that the blood is warmer than 37 °C
- The thermoregulatory centre in the brain processes the change
- It triggers the effectors: the skin blood vessels and the sweat glands
- Vasodilation and sweating increase the heat lost from the skin
- Core temperature falls back towards 37 °C and the correction stops
Two directions, one thermostat
Whichever way the temperature drifts, the same two effectors respond: the **skin blood vessels** and either the **sweat glands** or the **muscles**. What changes is the direction.
Hot day, cold night
Follow your body through a change in temperature, one response at a time.
- You are exercising on a hot day and your core temperature rises. What happens to the blood vessels supplying your skin?
- You still need to lose more heat. What else does your body do?
- That evening, waiting at a cold bus stop, your temperature drops. How do the skin blood vessels respond now?
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.