Adrenaline: The Fight or Flight Hormone Revision Notes | GCSE AQA Higher Biology

1. When Danger Strikes

Picture this: you're walking alone at night when you hear footsteps behind you. Instantly, your heart pounds, your breathing quickens, and you feel a surge of energy. This isn't panic — it's your body's ancient survival system kicking in.

This automatic response has kept humans alive for thousands of years. The chemical messenger responsible? Adrenaline — your body's emergency hormone.

2. Meet Your Body's Alarm System

Your adrenal glands sit like small caps on top of your kidneys. When your brain detects danger, it sends a signal down your spinal cord to these glands. Within seconds, they pump adrenaline into your bloodstream.

Trap: Many students think adrenaline is produced by the heart because that's where you feel the effects. Actually, it's made by the adrenal glands and travels to the heart via the blood.

3. The Body's Emergency Checklist

When adrenaline floods your system, it triggers a coordinated response across multiple organs. Think of it as your body running through an emergency checklist:

Heart: Rate increases from 70 beats per minute to over 100. This pumps more blood (and oxygen) to your muscles and brain.

Lungs: Breathing rate increases and airways widen. More oxygen enters your bloodstream.

Liver: Releases stored glucose into the blood. Your muscles need instant fuel for action.

Blood vessels: Those supplying muscles dilate (widen) while those to the digestive system constrict. Blood gets redirected to where it's needed most.

4. Why This System Evolved

The fight or flight response evolved when our ancestors faced life-or-death situations daily. Imagine encountering a predator — you need to either fight it or run away. Both options require maximum physical performance.

Adrenaline gives you superpowers for a few minutes: increased strength, faster reflexes, and heightened awareness. Stories of people lifting cars off trapped victims? That's adrenaline at work.

But there's a trade-off. Non-essential functions shut down temporarily — digestion slows, immune responses reduce, and growth processes pause. Your body prioritises immediate survival over long-term maintenance.

5. Modern Problems with Ancient Solutions

Here's the issue: your body can't tell the difference between a charging lion and an upcoming exam. Both trigger the same adrenaline response, but running away from your maths test isn't exactly helpful.

Chronic stress keeps adrenaline levels elevated, which can lead to problems: high blood pressure, difficulty sleeping, and digestive issues. The system designed to save your life occasionally can become problematic in modern society.

6. Exam Success Strategy

Worked example: Worked Example: Applying Adrenaline: The Fight or Flight Hormone

Use this method to answer an exam-style question about when danger strikes.

1. Underline the key term in the question and write a one-line definition linked to adrenaline: the fight or flight hormone. — This prevents vague answers and anchors the response in required terminology.
2. Describe the process in logical order using scientific vocabulary and direction words (increase/decrease, faster/slower). — Examiners award marks for clear causal chains, not isolated facts.
3. If data is provided, show each step of working and include units. — Method marks depend on visible working, even if the final answer is not fully correct.
4. Finish with a sentence explaining what the result shows about adrenaline: the fight or flight hormone. — Interpretation secures higher-band marks.

Answer: A complete response links mechanism, evidence, and conclusion for adrenaline: the fight or flight hormone.

Exam depth extension: In adrenaline: the fight or flight hormone, connect when danger strikes to meet your body's alarm system using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.

For 6-mark questions about hormones, use this structure: define the hormone, explain where it's produced, describe its effects on the body, and link these effects to survival advantage.