Hormones — Cambridge IGCSE Biology
Hormones and endocrine glands, how hormonal and nervous control compare, and the effects of adrenaline.
Revision notes
2 short notes, in the order of the specification. Each one in short:
A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs. Endocrine glands include the adrenal glands (adrenaline), pancreas (insulin), testes (testosterone) and ovaries (oestrogen). Compared with nervous control, hormonal control is slower but its effects last longer.
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.
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Quick check questions
Which gland secretes insulin?
Show answer
The pancreas.
Name the hormone made by the testes.
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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.
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.
How does adrenaline affect blood glucose?
Supplement Adrenaline increases the blood glucose concentration, so more glucose is available to the muscles. It also 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. Do not say adrenaline gives you energy.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026