Blood vessels (AQA GCSE Biology): Revision Notes
Blood vessels
What are blood vessels?
Your body has three different types of blood vessels that work together to transport blood around your body. These are called arteries, veins, and capillaries. Each type has a special job and is built differently to do that job well.
The three types of blood vessels form a complete transportation network in your body - think of them as different types of roads that all connect to move blood efficiently from your heart to your cells and back again.
Arteries
Arteries are the blood vessels that carry blood away from your heart. Think of them as the motorways of your circulatory system - they need to be strong and stretchy.
Structure of arteries
- Thick walls containing muscle and elastic fibres
- Small space inside (called the lumen) where blood flows
- High pressure blood flows through them
Why are arteries built this way?
The thick, muscular walls are important because:
- They can stretch when blood is pumped from your heart
- They don't burst under the high pressure
- They spring back to their original shape after stretching
- This helps push blood along to the next part of your body
Veins
Veins carry blood towards your heart. They're like the country roads of your circulatory system - wider but with less traffic pressure.
Structure of veins
- Thinner walls than arteries
- Large space inside (large lumen) for blood to flow
- Valves to stop blood flowing backwards
- Low pressure blood flows through them
Why are veins built this way?
- The large lumen gives blood more space to flow easily
- Valves work like one-way doors - blood can only flow towards your heart
- Blood gets squeezed through veins by your surrounding muscles when you move
- They don't need thick walls because the blood pressure is much lower
Capillaries
Capillaries are the smallest blood vessels in your body. They're like tiny lanes that connect the motorways (arteries) to the country roads (veins).
Structure of capillaries
- Very thin walls - only one cell thick
- Tiny space inside - usually just wide enough for one red blood cell
- Form networks called capillary beds
- Very low pressure blood flows through them
The Magic of Capillaries - Where Exchange Happens
The thin walls let substances pass through easily:
- Oxygen and glucose can move from blood into your body cells
- Waste products like carbon dioxide can move from cells into blood
- They reach almost every cell in your body
- The thin walls allow diffusion to happen quickly
Key differences summary
| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| Blood pressure | High | Low | Very low |
| Wall thickness | Thick | Thin | Very thin (one cell) |
| Lumen size | Small | Large | Tiny |
| Special features | Muscle + elastic fibres | Valves | Allow diffusion |
| Direction | Away from heart | To heart | Connect arteries to veins |
How they work together - The Complete Journey
- Heart pumps blood into arteries at high pressure
- Arteries carry blood to all parts of your body
- Capillaries allow oxygen and nutrients to reach your cells
- Veins collect blood and return it to your heart
- The cycle repeats!
Key Points to Remember:
- Arteries carry blood away from your heart (both start with 'A')
- Veins have valves to stop blood flowing backwards (both start with 'V')
- Capillaries are the connection between arteries and veins - they're where the important stuff happens!
- Arteries have thick walls for high pressure, veins have thin walls for low pressure
- Only capillaries allow substances to move in and out of the blood easily