1. KS4 Biology
Blood Vessels

2. Blood Vessels What are blood vessels? Arteries Veins Capillaries
Contents
Blood Vessels
What are blood vessels?
Arteries
Veins
Capillaries
Summary activities

3. Blood vessels and the circulatory system
The circulatory system is made up of the heart, blood and blood vessels.
What are blood vessels and what do they do?
Blood vessels are the network of tubes that carry the blood, pumped by the heart, around the body.

4. What is the total length of blood vessels?
Make a guess at the total length, in kilometres, of all the blood vessels in an adult human?
100, 000 kilometres
That’s more than twice the distance around the Earth
at the equator!
There are a lot of blood vessels so they must be important.
Are all blood vessels the same?

5. Different types of blood vessels
There are three types of blood vessels, as shown in this magnified part of the circulatory system.
blood from the heart
blood to the heart
artery
vein
Why are there different types of blood vessels?

6. Different types of blood vessels
The different blood vessels have different jobs to do in carrying blood around the body.
blood from the heart
blood to the heart
artery
vein
carries blood away from
the heart
carries blood back into
the heart
carries blood to and from the body’s cells
Do all blood vessels carry the same type of blood?

7. Blood Vessels What are blood vessels? Arteries Veins Capillaries
Contents
Blood Vessels
What are blood vessels?
Arteries
Veins
Capillaries
Summary activities

8. carries blood away from
What is an artery?
Arteries are the blood vessels that carry blood away from the heart.
blood from the heart
blood to the heart
carries blood away from
the heart
artery
Blood that is pumped from the heart to the body’s cells along the arteries is oxygen-rich.
Is this oxygen-rich blood under high or low pressure when
it leaves the heart?

9. Cross-section of an artery
The arteries carry blood at high pressure away from the heart.
Looking at the cross-section of an artery, why is it suitable for carrying blood at high pressure?
thick outer wall
thick inner layer
of muscle and
elastic fibres
narrow central tube

10. Blood flow in arteries – high pressure
Imagine using a hosepipe and covering half of the open end with your thumb. What happens to the pressure of the water?
The water is released under higher pressure and flows faster.
In the same way, arteries have
a narrow central core and thick muscular walls.
This means that blood from the heart is kept at high pressure and flows quickly to reach every part of the body, even the little toes!

11. Blood flow in arteries – stretching
With each heartbeat, a surge of blood enters the arteries and they expand to cope with the increased blood flow.
Which part of an artery allows it to expand?
thick inner layer
of muscle and
elastic fibres
increased
blood flow
The elastic fibres allow the artery to stretch under pressure. The muscle fibres contract to push the blood along and
keep it flowing.

12. Blood flow in arteries – detecting
There is a simple way of detecting how an artery stretches under the pressure of each heartbeat.
What is it?
You can feel your pulse because of the stretching of an artery that passes between bone and the surface of the skin.

13. Blood Vessels What are blood vessels? Arteries Veins Capillaries
Contents
Blood Vessels
What are blood vessels?
Arteries
Veins
Capillaries
Summary activities

14. carries blood back into
What is a vein?
Veins are the blood vessels that carry blood back into the heart.
blood from the heart
blood to the heart
vein
carries blood back into
the heart
Blood that travels from the body’s cells to the heart along the veins is oxygen-poor.
Is this oxygen-poor blood under high or low pressure as it returns to the heart?

15. Cross-section of a vein
The veins carry blood at low pressure back into the heart.
Looking at the cross-section of a vein, why is it suitable for carrying blood at low pressure?
thin outer wall
thin inner layer
of muscle and
elastic fibres
wide
central tube

16. Comparing cross-sections
Compare the cross-section of a vein
and an artery.
Why are they different?
Veins do not need to keep blood flowing quickly at high pressure and so they have much thinner walls than arteries.

17. Blood flow in veins – preventing backflow
Blood travels back to the heart in veins at low pressure.
If the blood pressure is too low, what, for example, might happen to the blood in leg veins?
blood
to the
heart
possible backflow
of blood
gravity
If low-pressure blood has to move against gravity, it might
slow down further and even flow in the wrong direction!

18. Blood flow in veins – valves
Veins have valves to prevent backflow.
backflow
prevented
vein valve
open
vein valve
closed
blood to the heart
When blood flows along veins it pushes past
the valves, which can
only open in one direction.
If blood in a vein does flow backwards,
it is trapped by
closed valves.

19. Blood flow in veins – muscle contraction
Veins have valves to prevent backflow. They also have thin walls and so need help from nearby muscles to push blood towards the heart.
How does this work? (Think of a tube of toothpaste!)
blood to the heart

20. Blood flow in veins – muscle contraction
Many veins are surrounded by muscles. When you move, these muscles contract and squeeze the veins.
This pushes blood along the veins back towards the heart. (Just like squeezing a tube of toothpaste!)
blood keeps flowing
to the heart
blood to the heart

21. Blood Vessels What are blood vessels? Arteries Veins Capillaries
Contents
Blood Vessels
What are blood vessels?
Arteries
Veins
Capillaries
Summary activities

22. What is a capillary? artery vein
Capillaries are the tiny blood vessels that carry a blood supply to and from the body’s cells.
What blood vessels are linked by capillaries?
artery
vein
Capillaries link arteries to veins.
Capillaries are the only blood vessels where substances can be exchanged between the blood and body cells.

23. Cross-section of a capillary
The capillaries carry blood to and from the body’s cells.
Looking at the cross-section of
a capillary, why is it suitable for the exchange of substances between the blood and body cells?

24. What happens in a capillary?
Capillaries have very thin walls for the exchange of substances between the blood and surrounding body cells.
How does this happen?
waste
products
useful
substances
Substances are exchanged
by diffusion.
Useful substances in the blood diffuse across the capillary wall into body cells.
Waste products from the body cells diffuse across the capillary wall into the blood.

25. Gas exchange in a capillary bed
A network of capillaries is called a capillary bed.
What gases are exchanged by diffusion in a capillary bed?
carbon
dioxide
oxygen
Oxygen in the blood diffuses across the capillary wall into body cells for respiration.
Carbon dioxide from the cells diffuses across the capillary wall into the blood.

26. Blood Vessels What are blood vessels? Arteries Veins Capillaries
Contents
Blood Vessels
What are blood vessels?
Arteries
Veins
Capillaries
Summary activities

27. Different blood vessels – activity

28. What do blood vessels do?

29. Which type of blood vessel?

30. Multiple-choice quiz