Adrenaline
Biology: Cambridge International GCSE Supplement, topic 14.3.4
Adrenaline
Adrenaline is a hormone released into the blood in times of stress, fear, or excitement. It is often called the “fight or flight” hormone because it prepares the body for action.
'Fight or flight' response
- Adrenaline is a hormone secreted by the adrenal glands, which sit on top of the kidneys.
- It is released when you are in an emergency or stressful situation.
- This is known as the 'fight or flight' response because adrenaline prepares the body for rapid action.
Adrenaline effects on the body
- Adrenaline's primary role is to increase metabolic activity to prepare your body for a sudden burst of energy:
- Increases breathing rate → more oxygen enters the blood.
- Increases heart rate → blood circulates faster to muscles and the brain.
- Increases pupil diameter → more light enters the eyes for better vision in dangerous situations.
Adrenaline in metabolic activity
- Increases blood glucose concentration:
- Stimulates the liver to break down glycogen into glucose – more sugar is released into your blood.
- This provides your muscles and brain with a burst of energy during emergencies.
- Increases heart rate:
- Adrenaline makes the heart beat faster.
- This pumps the extra oxygen and glucose to the muscles and brain more quickly.
Test yourself on Adrenaline
Why is adrenaline often called the “fight or flight” hormone?