Hormones
Chemical messengers
- A hormone is a chemical, made by a gland, carried in the blood.
- It changes the activity of one or more target organs.
- Hormones come from endocrine glands, which release them straight into the blood.
Practice
A hormone is a chemical that is:
Hormones are made by endocrine glands and travel in the blood to their target organs.
Some key hormones
| Gland | Hormone | Effect |
|---|---|---|
| adrenal glands | adrenaline | prepares the body for action |
| pancreas | insulin (and glucagon) | control blood glucose |
| testes | testosterone | male development |
| ovaries | oestrogen | female development |
- Adrenaline ('fight or flight'): raises heart rate, breathing rate, blood glucose and pupil size.
Practice
Adrenaline prepares the body for action by:
Adrenaline is the fight-or-flight hormone: it raises heart rate, breathing, blood glucose and pupil size.
Nerves vs hormones
| Nervous | Hormonal | |
|---|---|---|
| speed | very fast | slower |
| duration | short-lived | longer-lasting |
| travels as | impulses along neurones | chemicals in the blood |
Practice
Compared with nervous control, hormonal control is:
Hormones act more slowly but their effects last longer; nerves are fast and short-lived.
You've got it
Key idea
- a hormone = a chemical from a gland, carried in blood to target organs
- adrenaline = fight or flight (↑ heart rate, breathing, glucose, pupils)
- nerves are fast + short; hormones are slower + longer-lasting