Explain how adrenaline prepares the body for the 'fight or flight' response during a stressful situation such as running from danger.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
During a stressful situation, the adrenal glands release a hormone into the bloodstream. This hormone brings about several changes in the body within seconds.
Model answer (5 marks)
Adrenaline is released by the adrenal glands into the bloodstream.
It increases heart rate, which raises cardiac output.
It causes vasoconstriction of blood vessels in the skin and gut and vasodilation of vessels supplying skeletal muscle, so more blood flows to the muscles.
It stimulates glycogenolysis in the liver and muscle, raising blood glucose levels and providing more fuel for the muscles.
The combined rise in heart rate, blood flow to muscle and blood glucose raises blood pressure, ensuring oxygen and glucose reach the muscles quickly and enabling a rapid fight‑or‑flight response.
It increases heart rate, which raises cardiac output.
It causes vasoconstriction of blood vessels in the skin and gut and vasodilation of vessels supplying skeletal muscle, so more blood flows to the muscles.
It stimulates glycogenolysis in the liver and muscle, raising blood glucose levels and providing more fuel for the muscles.
The combined rise in heart rate, blood flow to muscle and blood glucose raises blood pressure, ensuring oxygen and glucose reach the muscles quickly and enabling a rapid fight‑or‑flight response.
Examiner tips
- Use the exact terms: adrenaline, heart rate, blood flow, glycogenolysis, blood pressure. Show the causal chain: adrenaline → physiological changes → faster response. Keep each point brief but complete to earn the 5 marks.
Common mistakes
- Confusing adrenaline with cortisol or omitting the rise in blood glucose. Using vague phrases like "more oxygen" without linking to increased blood flow or heart rate. Writing a long paragraph instead of clear, separate points.
Mark scheme (5 marks)
- Adrenaline is produced/released by the adrenal glands
- Adrenaline increases heart rate
- Adrenaline increases blood flow to the muscles / so muscles receive more oxygen and glucose
- Adrenaline increases blood glucose levels / causes glycogen to be broken down to glucose
- Adrenaline increases blood pressure / so oxygen and glucose are delivered more rapidly to muscles for respiration / enabling a faster response to the stressor
Key terms in this question
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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