Adrenalin and fight or flight

Animal coordination, control and homeostasis · Hormones and the endocrine system · note 2 of 3

Spec 7.2

Higher tier

Higher tier: only on the Higher tier papers. Foundation students can skip it. What the labels mean

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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.

The effects of adrenalin
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 Combined Science (1SC0) specification · Updated October 2026

Frequently asked questions

Why are hormones called chemical messengers?

Hormones are called chemical messengers because they are chemicals that carry a signal from one part of the body to another. They are made in endocrine glands and released straight into the blood, which carries them around the whole body in the plasma. Each hormone only causes a response in its target organs.

What does the pituitary gland do?

Higher tier The pituitary gland is an endocrine gland at the base of the brain that releases hormones that control other glands and organs. It releases FSH and LH, which act on the ovaries in the menstrual cycle, and TSH, which acts on the thyroid gland and makes it produce thyroxine.

What does adrenalin do to the body?

Higher tier Adrenalin prepares the body for fight or flight. It increases heart rate and blood pressure, so blood is pumped to the organs faster, and increases blood flow to the muscles, giving them more oxygen and glucose for respiration. It also stimulates the liver to change glycogen into glucose, which raises the blood sugar level.

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