GCSE Biology · Edexcel 1BI0 · Topic 7A
Hormones and the endocrine system
Key points
- Hormones are chemicals secreted by endocrine glands into the blood, which carries them to target organs.
- Glands: pituitary (the master gland), thyroid, adrenal glands, pancreas, ovaries and testes.
- Hormone responses are slower and last longer than nervous responses, which are fast, short and precise.
- Adrenaline from the adrenal glands increases heart rate, blood flow to muscles and blood glucose, preparing the body for 'fight or flight'.
- Thyroxine from the thyroid controls metabolic rate. It is controlled by negative feedback: low thyroxine causes the pituitary to release TSH, which stimulates the thyroid; high thyroxine reduces TSH.
- Negative feedback means a change triggers a response that reverses it, keeping levels steady.
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Hormones are the body's chemical messengers. This sub-topic covers where they are made, how they differ from nerve impulses, and two examples, adrenaline and thyroxine, including how negative feedback keeps a hormone level steady.
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