How does the body keep its core temperature stable?
Explain how the body regulates core temperature through negative feedback and the responses to heat and cold
The hypothalamus regulates core temperature by negative feedback; cooling responses (sweating, vasodilation) and warming responses (shivering, vasoconstriction) reverse changes.
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What this dot point is asking
You need to explain why temperature must be controlled, identify the control centre and receptors, and describe the specific cooling and warming responses as a negative feedback loop.
Why temperature must be regulated
Body temperature must stay close to the set point of about 37 degrees Celsius because the body's reactions are controlled by enzymes, which have an optimum temperature. Too hot and enzymes denature; too cold and reactions become too slow. Keeping temperature stable keeps metabolism working efficiently.
Humans are endotherms: we generate heat internally and regulate temperature physiologically, unlike ectotherms which rely mainly on behaviour and the environment.
The control centre
The hypothalamus in the brain is the control centre for temperature. It contains receptors that monitor blood temperature, and it receives information from temperature receptors in the skin. When core temperature moves from the set point, the hypothalamus coordinates a corrective response, communicating through nerves and hormones.
Responses to overheating
When body temperature rises above the set point, the responses increase heat loss:
- Sweating - sweat on the skin evaporates, and evaporation removes heat from the body.
- Vasodilation - blood vessels near the skin surface widen, so more warm blood flows close to the surface and loses heat to the surroundings.
- Reduced metabolic activity and behaviour such as removing clothing or seeking shade.
These responses cool the body back toward the set point, then switch off.
Responses to cooling
When body temperature falls below the set point, the responses conserve and generate heat:
- Vasoconstriction - surface blood vessels narrow, reducing blood flow to the skin and limiting heat loss.
- Shivering - rapid muscle contractions generate heat through respiration.
- Raised metabolic rate - thyroxine and adrenaline can increase heat production.
- Erect hair (piloerection) and behavioural responses such as adding clothing.
Exam-style practice questions
Practice questions written in the style of SACE Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
2018 SACE Stage 21 marksA flow chart shows the response to a decrease in body temperature: hypothalamus releases TRH, pituitary releases TSH, and the thyroid gland releases hormone X. State the name of hormone X.Show worked answer →
Hormone X is thyroxine (also accepted: thyroid hormone, or T3/T4). The thyroid gland releases thyroxine in response to TSH, and thyroxine raises the metabolic rate to generate heat. The mark is for naming thyroxine.
2018 SACE Stage 23 marksHormone X (thyroxine) is released by the thyroid gland in response to a decrease in body temperature. Explain how hormone X affects body temperature.Show worked answer →
Three points cover the marks.
Thyroxine travels in the blood to target cells throughout the body.
It increases the rate of cellular respiration (metabolic rate) in these cells.
Respiration releases heat energy as a by-product, so a higher metabolic rate generates more heat, raising body temperature back toward the set point. This is the corrective response in negative feedback control of temperature.
2019 SACE Stage 22 marksWhen a person has a lower-than-normal body temperature, describe how the nervous system regulates body temperature in human beings.Show worked answer →
For 2 marks, give a nervous response that conserves or generates heat.
The hypothalamus, via the nervous system, sends nerve impulses to skeletal muscles to cause shivering: rapid muscle contractions that generate heat through respiration.
Nerve impulses also cause vasoconstriction of skin blood vessels (arterioles), reducing blood flow near the skin surface so less heat is lost. Both responses raise or conserve body heat, returning temperature toward 37 degrees C.