Adrenaline, thyroxine and negative feedback

Homeostasis and response · Hormonal coordination in humans · note 7 of 7

Spec 4.5.3.7

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Adrenaline, thyroxine and negative feedbackSpec 4.5.3.7

In short

Adrenaline is a hormone produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for flight or fight. Thyroxine from the thyroid gland stimulates the basal metabolic rate, and its level is controlled by negative feedback.

Adrenaline

Adrenaline is produced by the adrenal glands in times of fear or stress. It increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’.

Thyroxine

Thyroxine from the thyroid gland stimulates the basal metabolic rate. It plays an important role in growth and development.

Negative feedback

Thyroxine levels are controlled by negative feedback. If the thyroxine level in the blood becomes too high, less thyroxine is released, so the level falls. If it becomes too low, more is released, so the level rises. A change in the level is reversed to bring it back to normal.

Exam tip:

Negative feedback means the response reverses the original change. Say what changed, which way the body responds, and that the level returns towards normal.

Quick check

What is a hormone?
Show answer
A chemical secreted by a gland directly into the bloodstream, which acts on a target organ.
Which hormone lowers blood glucose concentration, and where is it made?
Show answer
Insulin, made in the pancreas.
Compare the cause of Type 1 and Type 2 diabetes.
Show answer
Type 1: the pancreas fails to produce enough insulin. Type 2: the body cells no longer respond to insulin.
Name the hormone that causes the release of the egg.
Show answer
Luteinising hormone (LH).
Give two non-hormonal methods of contraception.
Show answer
Any two of: condoms, diaphragms, spermicidal agents, abstaining, surgical sterilisation (non-hormonal intrauterine devices also accepted).

Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026

Frequently asked questions

What does insulin do to blood sugar?

Insulin lowers blood sugar (blood glucose concentration). The pancreas produces insulin when blood glucose is too high, for example after a meal. Insulin causes glucose to move from the blood into the cells, and in liver and muscle cells excess glucose is converted to glycogen for storage. Blood glucose then falls back to the normal level.

What is the difference between insulin and glucagon?

Higher tier Insulin lowers blood glucose and glucagon raises it. Both are made by the pancreas. Insulin is released when blood glucose is too high and makes glucose move from the blood into cells. Glucagon is released when it is too low and causes glycogen to be converted into glucose and released into the blood. They work in a negative feedback cycle.

Why are hormones called chemical messengers?

Hormones are called chemical messengers because they are chemicals secreted by glands directly into the bloodstream, which carries them to a target organ where they produce an effect. Compared with nerve impulses, hormones act more slowly but their effects last longer. They reach every part of the body but only affect their target organ.

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