A patient is admitted to hospital with a core body temperature of 40.8 °C following prolonged exercise in hot conditions. Explain how the hypothalamus coordinates the physiological responses that act to reduce core body temperature back to the normal set point.

OCR A-Level Biology A (H420) — 5.1 Communication and homeostasis · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The hypothalamus contains thermoreceptors that sense the rise in blood temperature above the normal set point. It then sends efferent nerve impulses to effectors in the skin. These impulses cause vasodilation of arterioles in the skin, increasing blood flow to the surface and thereby increasing heat loss by radiation. Simultaneously, the hypothalamus stimulates sweat glands, leading to increased sweating. The evaporation of sweat from the skin removes latent heat, further reducing core body temperature.

Examiner tips

  • Use the word "thermoreceptors" and "set point" to show understanding of the hypothalamic role.
  • Show the sequence: detection → nerve impulses → vasodilation and sweating.
  • Mention both radiation and evaporation as heat loss mechanisms.
  • Keep the answer concise and use correct UK spelling.

Common mistakes

  • Using vague terms like "brain" instead of "hypothalamus".
  • Omitting the efferent nerve impulse step.
  • Failing to mention both vasodilation and sweating as separate responses.

Mark scheme (4 marks)

  1. The hypothalamus thermoreceptors detect the rise in blood temperature above the set point
  2. The hypothalamus sends nerve impulses via the efferent nervous system to effectors in the skin
  3. Vasodilation of arterioles in the skin increases blood flow to the surface, increasing heat loss by radiation
  4. Increased sweating causes evaporation of water from the skin surface, removing latent heat from the body

Key terms in this question

hypothalamus · set point

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