Adrenaline

Coordination and response · Hormones · note 2 of 2

Spec 14.3.3, 14.3.6Download all Hormones notes (PDF)Download all notes (PDF)4 pages

AdrenalineSpec 14.3.3, 14.3.6

In short

Adrenaline is the hormone secreted by the adrenal glands in fight or flight situations. It increases breathing rate, heart rate and pupil diameter. Adrenaline also increases the blood glucose concentration, so more glucose, and oxygen, reach the muscles quickly. The muscle cells use this glucose in respiration to release energy for movement.

Adrenaline is the hormone secreted by the adrenal glands in ‘fight or flight’ situations. These are moments of danger or stress when the body must get ready to fight or run away.

Increased breathing rate
Increased heart rate
Increased pupil diameter

These changes get more oxygen and glucose to the muscles quickly, and let more light into the eyes so the person can see the danger better.

Supplement

Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Adrenaline and metabolic activity

Supplement

Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Adrenaline also controls metabolic activity. It increases the blood glucose concentration and increases heart rate.

Supplement

Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean

Adrenaline increases the blood glucose concentration, so more glucose is available to the muscles.
Adrenaline increases heart rate, so this glucose, and oxygen, reach the muscles more quickly.
The muscle cells use the glucose in respiration to release energy for movement.

Common mistake:

Adrenaline is spelt with an e at the end. Do not write that it ‘gives you energy’. It raises blood glucose so cells can release energy by respiration.

Quick check

Which gland secretes insulin?
Show answer
The pancreas.
Name the hormone made by the testes.
Show answer
Testosterone.
Which type of control has the longer-lasting effect, nervous or hormonal?
Show answer
Hormonal.
Supplement State two ways adrenaline affects the metabolic activity of the body.
Show answer
It increases blood glucose concentration and increases heart rate.

Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026

Frequently asked questions

Why are hormones called chemical messengers?

Hormones are called chemical messengers because they are chemical substances that carry a signal through the blood. A hormone is produced by a gland, carried by the blood, and alters the activity of one or more specific target organs. The blood carries it around the whole body, but it only affects its target organs.

What is the difference between nervous and hormonal control?

Nervous control is very fast and its effect is short, while hormonal control is slower and its effect lasts longer. Nervous impulses travel quickly along neurones, and the effect stops soon after the impulse stops. Hormones travel in the blood, so they act more slowly, but their effect can last minutes, hours or longer.

What does adrenaline do to the body?

Adrenaline prepares the body for fight or flight. It is secreted by the adrenal glands in moments of danger or stress, and it increases breathing rate, heart rate and pupil diameter. These changes get more oxygen and glucose to the muscles quickly and let more light into the eyes so the danger can be seen.

All 4 questions on Hormones

Finished hormones? Test yourself:Exam questions Flashcards