© Boardworks Ltd 2004 1 of 30 KS4 Biology Blood Vessels
© Boardworks Ltd 20041 of 30
KS4 Biology
Blood Vessels
© Boardworks Ltd 20042 of 30
Contents
Blood Vessels
What are blood vessels?
Arteries
Capillaries
Summary activities
Veins
© Boardworks Ltd 20043 of 30
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.
© Boardworks Ltd 20044 of 30
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?
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?
100, 000 kilometres100, 000 kilometres
© Boardworks Ltd 20045 of 30
There are three types of blood vessels, as shown in this magnified part of the circulatory system.
Different types of blood vessels
Why are there different types of blood vessels?
blood from the heart
blood to the heart
artery vein
© Boardworks Ltd 20046 of 30
Different types of blood vessels
The different blood vessels have different jobs to do in carrying blood around the body.
veincarries blood
back intothe heart
arterycarries blood
away fromthe heart
Do all blood vessels carry the same type of blood?
blood to the heart
blood from the heart
carries blood to and from the
body’s cells
© Boardworks Ltd 20047 of 30
Contents
Blood Vessels
What are blood vessels?
Arteries
Capillaries
Summary activities
Veins
© Boardworks Ltd 20048 of 30
What is an artery?
Arteries are the blood vessels that carry blood away from the heart.
Is this oxygen-rich blood under high or low pressure when
Blood that is pumped from the heart to the body’s cells along the arteries is oxygen-rich.
blood to the heart
blood from the heart
carries blood away fromthe heart
artery
it leaves the heart?
© Boardworks Ltd 20049 of 30
Cross-section of an artery
thick outer wall
thick inner layerof muscle and elastic fibres
narrow central tube
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?
© Boardworks Ltd 200410 of 30
Blood flow in arteries – high pressure
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!
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.
© Boardworks Ltd 200411 of 30
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 andkeep it flowing.
© Boardworks Ltd 200412 of 30
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.
© Boardworks Ltd 200413 of 30
Contents
Blood Vessels
What are blood vessels?
Arteries
Capillaries
Summary activities
Veins
© Boardworks Ltd 200414 of 30
What is a vein?
Veins are the blood vessels that carry blood back into the heart.
Is this oxygen-poor blood under high or low pressure as it returns to the heart?
Blood that travels from the body’s cells to the heart along the veins is oxygen-poor.
blood to the heart
blood from the heart
veincarries blood
back intothe heart
© Boardworks Ltd 200415 of 30
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?
Cross-section of a vein
thin outer wall
thin inner layerof muscle and elastic fibres
wide central tube
© Boardworks Ltd 200416 of 30
Compare the cross-section of a vein
Comparing cross-sections
Veins do not need to keep blood flowing quickly at high pressure and so they have much thinner walls than arteries.
and an artery.
Why are they different?
© Boardworks Ltd 200417 of 30
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?
gravity
blood to the heart possible
backflow of blood
If low-pressure blood has to move against gravity, it mightslow down further and even flow in the wrong direction!
© Boardworks Ltd 200418 of 30
Blood flow in veins – valves
Veins have valves to prevent backflow.
blood to the heart
backflow prevented vein valve
open vein valve closed
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.
© Boardworks Ltd 200419 of 30
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
© Boardworks Ltd 200420 of 30
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 flow in veins – muscle contraction
blood to the heart
blood keeps
flowing to the heart
© Boardworks Ltd 200421 of 30
Contents
Blood Vessels
What are blood vessels?
Arteries
Capillaries
Summary activities
Veins
© Boardworks Ltd 200422 of 30
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?
What is a capillary?
Capillaries link arteries to veins.
Capillaries are the only blood vessels where substances can be exchanged between the blood and body cells.
artery vein
© Boardworks Ltd 200423 of 30
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?
© Boardworks Ltd 200424 of 30
Capillaries have very thin walls for the exchange of substances between the blood and surrounding body cells.
How does this happen?
What happens in a capillary?
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.
usefulsubstances
wasteproducts
© Boardworks Ltd 200425 of 30
Gas exchange in a capillary bed
oxygen
carbondioxide
A network of capillaries is called a capillary bed.
What gases are exchanged by diffusion in a capillary bed?
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.
© Boardworks Ltd 200426 of 30
Contents
Blood Vessels
What are blood vessels?
Arteries
Capillaries
Summary activities
Veins
© Boardworks Ltd 200427 of 30
Different blood vessels – activity
© Boardworks Ltd 200428 of 30
What do blood vessels do?
© Boardworks Ltd 200429 of 30
Which type of blood vessel?
© Boardworks Ltd 200430 of 30
Multiple-choice quiz