Hormones and the Endocrine System — AQA GCSE Biology
The endocrine system uses chemical messengers called hormones to control many body processes.
What is the endocrine system?
The endocrine system is made of glands that secrete hormones directly into the bloodstream. The blood carries the hormone to target organs, where it produces an effect.
Compared with the nervous system, hormonal responses are usually:
- slower to act, but
- longer lasting and more widespread.
The main glands
- Pituitary gland — the "master gland" in the brain; it releases several hormones that act on other glands to coordinate the body.
- Thyroid — releases thyroxine, controlling metabolic rate.
- Pancreas — controls blood glucose (insulin and glucagon).
- Adrenal glands — release adrenaline for "fight or flight".
- Ovaries — release oestrogen (and progesterone).
- Testes — release testosterone.
Nervous vs hormonal
| Nervous | Hormonal | |
|---|---|---|
| Message carried by | electrical impulses | chemicals (hormones) |
| Speed | fast | slower |
| Duration | short | long-lasting |
| Travels via | neurones | bloodstream |
Exam tips
- Define a hormone as a chemical messenger carried in the blood to target organs.
- The pituitary is the master gland.
- Learn the main glands and their hormones.
- Compare nervous and hormonal responses (speed and duration).