How does the body hold its core temperature near 37 degrees whether it is freezing or sweltering outside?
Explain how the body regulates core temperature by negative feedback, including the role of the hypothalamus, thermoreceptors and the effectors that control heat loss and heat gain
A focused answer to the WACE Year 12 Human Biology Unit 3 dot point on thermoregulation. The hypothalamus and thermoreceptors, the effectors for heat loss (sweating, vasodilation) and heat gain (shivering, vasoconstriction), and the four routes of heat transfer.
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What this dot point is asking
WACE wants you to apply the stimulus-response and negative-feedback model to one named variable, core temperature, naming the receptor, the control centre, and the effectors for both directions. Temperature must be regulated because enzymes work within a narrow range; too hot and enzymes denature, too cold and reactions slow too much.
The control centre and receptors
The hypothalamus is the body's thermostat. It contains the set point (about 37 degrees Celsius) and receives information from two sets of thermoreceptors: peripheral thermoreceptors in the skin that monitor the external temperature, and central thermoreceptors in the hypothalamus itself that monitor the temperature of the blood. The hypothalamus compares this input against the set point and activates the appropriate effectors.
Responding when the body is too hot
If core temperature rises above the set point, the hypothalamus triggers responses that increase heat loss:
- Sweating: sweat glands secrete sweat onto the skin; as it evaporates it carries heat away.
- Vasodilation: arterioles supplying the skin widen, so more warm blood flows near the surface and heat radiates away. This is why pale skin looks flushed when hot.
- Reduced metabolic activity and behaviour: less heat is generated, and behaviours like removing clothing or seeking shade help.
These responses lower core temperature back toward the set point, which is negative feedback because the response opposes the stimulus.
Responding when the body is too cold
If core temperature falls below the set point, the hypothalamus triggers responses that increase heat gain and reduce heat loss:
- Vasoconstriction: arterioles to the skin narrow, so less warm blood reaches the surface and less heat is lost.
- Shivering: rapid involuntary muscle contractions generate heat through respiration.
- Raised metabolic rate: hormones such as thyroxine and adrenaline increase the metabolic rate, producing more heat.
- Erection of body hair (piloerection): traps a layer of insulating air, more useful in furry mammals than in humans.
Routes of heat transfer
Heat moves between the body and the environment by radiation (heat given off as infrared), conduction (direct contact with cooler objects), convection (heat carried away by moving air or water), and evaporation (heat used to evaporate sweat). Sweating relies on evaporation, which is why it is far less effective in humid conditions where sweat cannot evaporate.
How this maps to the exam
Expect to be asked to write the full thermoregulation feedback loop for either heating or cooling, name the control centre and receptors, or explain why a particular effector works (for example why sweating cools or why vasoconstriction conserves heat). You may be asked why sweating is less effective on a humid day, which tests the evaporation route of heat loss.