Adrenaline is a hormone released during the 'fight-or-flight' response. Explain how adrenaline reaches its target organs and describe the effects it produces in the body to prepare an organism for danger.

Eduqas A-Level Biology — 4.4 Application of reproduction and genetics · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Adrenaline is produced and secreted by the adrenal glands.
It is released into the bloodstream and travels to target organs.
In the heart it binds to β‑adrenergic receptors, increasing heart rate and pulse.
In the lungs it stimulates bronchioles to dilate, raising breathing rate and blood flow to muscles.
It also activates glycogenolysis in liver and muscle, converting glycogen to glucose and raising blood sugar, providing energy for the heightened activity.

Examiner tips

  • Use the word "binds" to show receptor action. Mention β‑adrenergic receptors. Include both heart and lungs as target organs. Show the metabolic effect on glycogen.
  • common_mistakes
  • :
  • Failing to mention the adrenal gland as the source. Omitting the bloodstream route. Confusing adrenaline with cortisol or omitting glycogenolysis.

Mark scheme (5 marks)

  1. Adrenaline is produced/secreted by the adrenal gland
  2. Adrenaline travels in the bloodstream to target organs
  3. Adrenaline increases heart rate / pulse rate
  4. Adrenaline increases breathing rate / blood flow to muscles
  5. Adrenaline causes glycogen to be converted into glucose, increasing blood sugar levels / providing energy for respiration

Key terms in this question

adrenaline · hormone · target organ

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