Adrenalin and fight or flightSpec 7.2
In short
Adrenalin is a hormone produced by the adrenal glands that prepares the body for fight or flight. It increases heart rate, blood pressure and blood flow to the muscles, so the muscles get more oxygen and glucose for respiration. It also raises the blood sugar level by stimulating the liver to change glycogen into glucose.
Adrenalin is produced by the adrenal glands. It prepares the body for fight or flight, for example when you are frightened or in danger. It makes the body ready to use a lot of energy quickly.
| Effect | Why it helps |
|---|---|
| Increased heart rate | Blood is pumped around the body faster |
| Increased blood pressure | Blood is pushed to the organs more quickly |
| Increased blood flow to the muscles | Muscles get more oxygen and glucose for respiration, so they can release more energy |
| Raised blood sugar level | Adrenalin stimulates the liver to change glycogen into glucose, which is released into the blood |
Exam tip:
Name the liver and say glycogen is changed into glucose. ‘Sugar is released’ on its own is too vague for the mark.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026