Hormones (AQA GCSE Biology): Revision Notes
Hormones
What is the endocrine system?
The endocrine system is made up of glands that release hormones straight into your blood. These hormones travel around your body and affect different organs.
The endocrine system works alongside your nervous system to control and coordinate your body's functions. While your nervous system sends electrical signals through nerves, your endocrine system uses chemical messengers (hormones) that travel through your bloodstream.
What are hormones?
A hormone is a chemical messenger that:
- Gets made by a gland in your body
- Travels through your bloodstream
- Changes how a target organ works
Think of hormones like letters in the post - they carry important messages from one part of your body to another.
The pituitary gland - the "master gland"
The pituitary gland sits in your brain and is called the "master gland" because it controls other glands.
The pituitary gland is crucial for coordinating your body's hormone system. When your body needs to respond to changes, the pituitary gland releases hormones. These hormones then tell other glands to release their own hormones. It's like the pituitary gland is the boss giving orders to other glands.
How hormones compare to nerve impulses
Your body has two main ways to send messages - through hormones and through nerves. Here's how they're different:
| Hormones | Nerve impulses |
|---|---|
| Work slowly | Work very fast |
| Effects last a long time | Effects are short |
Real-life Example: Fear Response
If you see something scary, nerve impulses make you jump quickly (within milliseconds). But hormones like adrenalin keep your heart beating fast for much longer (minutes to hours), preparing your body to deal with the threat.
Different glands make different hormones
Your body has several important glands, each making specific hormones for different functions:
Pituitary gland
- Makes FSH (follicle-stimulating hormone)
- Makes LH (luteinising hormone)
- Both of these affect the ovaries
Thyroid gland
- Makes thyroxine
- Controls how fast your body uses energy
Pancreas
- Makes insulin
- Controls blood sugar levels
- Targets the liver and muscles
Adrenal glands
- Make adrenalin
- Prepares your body for action in emergencies
Reproductive glands
- Ovaries make oestrogen and progesterone
- Testes make testosterone
- These control sexual development and reproduction
Each gland has evolved to produce specific hormones that control particular body functions. This specialisation ensures that your body can fine-tune different processes independently while still maintaining overall coordination.
Target organs
Each hormone only affects specific organs called "target organs". The hormone-target organ relationship is highly specific:
- Insulin targets the liver and muscles
- FSH and LH target the ovaries
- Testosterone targets male reproductive organs
This is like having a key that only fits certain locks - each hormone only works on specific organs.
Why Specificity Matters: This targeting system prevents hormones from affecting organs they shouldn't. If insulin affected all organs instead of just liver and muscles, it would cause serious problems throughout your body. The lock-and-key system ensures hormones only affect their intended targets.
Key Points to Remember:
- Hormones are chemical messengers made by glands
- They travel in your blood to reach target organs
- The pituitary gland controls other glands (it's the "master gland")
- Hormones work slowly but have long-lasting effects
- Different glands make different hormones for different jobs
- Each hormone only affects specific target organs