Describe the effects of adrenaline on the body during a 'fight or flight' response.

Cambridge International IGCSE Biology (0610) — 14.3 Hormones · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Adrenaline released from the adrenal medulla during a fight or flight response:
1. Increases heart rate by stimulating β1‑adrenergic receptors in the sino‑atrial node.
2. Raises breathing rate through β2‑adrenergic stimulation of the respiratory centre and bronchi.
3. Dilates the pupils (mydriasis) via α1‑adrenergic receptors in the iris dilator muscle.
4. Raises blood glucose concentration by activating glycogenolysis in the liver through β2‑adrenergic receptors.

Examiner tips

  • Use the exact terms ‘β1‑adrenergic’, ‘β2‑adrenergic’, ‘α1‑adrenergic’ where appropriate; examiners look for receptor detail.
  • Show the sequence: adrenaline → receptor → physiological effect. Mention the organ (heart, lungs, iris, liver) to demonstrate understanding.
  • Keep each point brief but complete – one sentence per mark.
  • Use UK spelling (e.g., ‘adrenaline’, ‘heart rate’).

Common mistakes

  • Confusing adrenaline with noradrenaline or omitting receptor names. Failing to specify the organ (e.g.
  • just saying
  • heart" instead of "sino‑atrial node

Mark scheme (4 marks)

  1. Adrenaline increases heart rate
  2. Adrenaline increases breathing rate
  3. Adrenaline widens / dilates the pupils
  4. Adrenaline increases blood glucose concentration by converting glycogen to glucose in the liver

Key terms in this question

adrenaline

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