Hormones (AQA GCSE Biology Combined Science): Revision Notes
Hormones
What are hormones?
A hormone is a special chemical messenger made by your body. Hormones have three important features:
Three Key Features of Hormones:
- They are made and released by glands
- They travel around your body in your bloodstream
- They affect specific organs called target organs
Think of hormones like letters in the post - they carry messages from one part of your body to another!
The endocrine system
The endocrine system is made up of glands that make hormones. These glands release hormones directly into your bloodstream rather than through tubes.
The pituitary gland is often called the "master gland" because it controls other glands. It sits in your brain and releases several different hormones. When your body needs to respond to changes, the pituitary gland releases hormones that tell other glands what to do.
The pituitary gland acts as the body's control centre, coordinating the activity of other hormone-producing glands throughout your body.
How hormones work
When a gland releases a hormone, it travels through your bloodstream until it reaches its target organ. The target organ then responds by changing what it does.
Worked Example: How Insulin Works
Step 1: You eat food containing sugar Step 2: Your pancreas detects the rise in blood sugar Step 3: The pancreas releases insulin into your bloodstream Step 4: Insulin travels to your liver and muscles Step 5: These organs respond by taking in glucose from your blood
Hormones vs nerve impulses
Hormones and nerve impulses both help your body respond to changes, but they work differently:
Hormones:
- Work slowly
- Have long-lasting effects
- Travel through blood
Nerve impulses:
- Work fast
- Have short effects
- Travel along nerves
Understanding the difference between hormonal and nervous responses is crucial - hormones provide sustained, body-wide control while nerves give rapid, localised responses.
Major glands and their hormones
Your body has several important glands that make different hormones:
Pituitary gland (in your brain):
- Makes FSH and LH (affect reproductive organs)
Thyroid gland (in your neck):
- Makes thyroxine (controls metabolism)
Pancreas (near your stomach):
- Makes insulin (controls blood sugar)
Adrenal glands (above your kidneys):
- Make adrenalin (prepares body for action)
Ovaries (in females):
- Make oestrogen and progesterone (control female reproduction)
Testes (in males):
- Make testosterone (controls male reproduction)
Each gland has a specific location in your body and produces hormones with particular functions. Learning where these glands are located helps you understand how hormones affect different parts of your body.
Target organs
Each hormone affects specific target organs:
Hormone-Target Organ Relationships:
- FSH and LH target the ovaries
- Insulin targets the liver and muscles
- Oestrogen affects ovaries, uterus and pituitary gland
- Progesterone targets the uterus
- Testosterone affects male reproductive organs
Remember!
Key Points to Remember:
- Hormones are chemical messengers made by glands
- They travel in your bloodstream to reach target organs
- The pituitary gland is the "master gland" that controls others
- Hormones work more slowly than nerves but last longer
- Different glands make different hormones for different jobs
- Each hormone has specific target organs it affects