# Explain how the hormone thyroxine is regulated in the body using a negative feedback cycle.

> AQA GCSE Biology (8461) — 4.5.1 Homeostasis · Explain · 4 marks

## Mark scheme (4 marks)

1. Thyroxine is produced by the thyroid gland and increases the metabolic rate
2. When thyroxine levels in the blood are high, the brain/pituitary gland detects this and reduces the release of the hormone that stimulates thyroxine production
3. This causes the thyroid gland to produce less thyroxine, so levels fall back towards the optimum
4. This is a negative feedback cycle because the change (high thyroxine) is reversed / the system reverses the original change to maintain optimum conditions

## Key terms

- [thyroxine](https://www.gradenine.co.uk/glossary/thyroxine)
- [negative feedback cycle](https://www.gradenine.co.uk/glossary/negative-feedback-cycle)

## Related

- [Revision notes for AQA GCSE Biology (8461)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-hormone-thyroxine-is-33d11e86) · Published by Druglandscape Ltd.