© boardworks ltd 2004 1 of 30 ks4 biology blood vessels

© Boardworks Ltd 20041 of 30

KS4 Biology

Blood Vessels


Contents

Blood Vessels

What are blood vessels?

Arteries

Capillaries

Summary activities

Veins


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.


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


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


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


carries blood to and from the

body’s cells


Contents

Blood Vessels


Arteries

Capillaries

Summary activities

Veins


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


carries blood away fromthe heart

artery

it leaves the heart?


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?


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.


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.


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.


Contents

Blood Vessels


Arteries

Capillaries

Summary activities

Veins


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


veincarries blood

back intothe heart


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


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?


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!


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.


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


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


Contents

Blood Vessels


Arteries

Capillaries

Summary activities

Veins


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


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?


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


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.


Contents

Blood Vessels


Arteries

Capillaries

Summary activities

Veins


Different blood vessels – activity


What do blood vessels do?


Which type of blood vessel?


Multiple-choice quiz

© boardworks ltd 2004 1 of 30 ks4 biology blood vessels

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