© Boardworks Ltd 2003 The Breathing System Key Stage 4

© Boardworks Ltd 2003

The Breathing System

Key Stage 4


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Oxygen (O2)

Carbon Dioxide (CO2)

Humans breathe to ensure that oxygen enters the body

and that carbon dioxide leaves the body.


Let us now look at the structure of the breathing system.The human body can be divided into three regions.

The breathing system is found in the thorax.

THORAX

ABDOMEN

HEAD

The breathing system


The body separates the process of breathing in andbreathing out.

Breathing in is one process and is known as…

Inhalation

(When we breathe in we inhale)

Breathing out is another separate process and is known as…

Exhalation(When we breathe out we exhale)

By separating these two processes, the body can concentrate on

the two tasks in turn.


Firstly it must inhale oxygen and secondly it must exhale

carbon dioxide

The breathing system is designed to be able to perform both tasks using the same organs.

One final important fact to remember is that breathing can be performed without humans having to think about it.

Just imagine that as well as everything else you have to think about, you would have to remember to tell your body to inhale,

then exhale, then inhale, exhale, inhale, … etc.

There would be no time for anything else.


So, what does this system look like?

Well, let us start where air enters the system…

Air enters through either the mouth or the nostrils.

Mouth

It does not matter through which opening the air enters because the oral and nasal cavities are connected.

Nostril Nasal cavity

Oral Cavity


As the air passes through the nasal cavity, the air is smelt, warmed, filtered and moistened slightly.The air meets at the Pharynx, a junction at back of the oral cavity.

The Pharynx is a junction between two tubes. The air must travel down only one of these tubes. One is the Windpipe (Trachea) and the other is the Gullet (Oesophagus)

Trachea

Gullet

As the name suggests, air must pass down through the windpipe (trachea).


You may be wondering why they are C-shaped and not full circles.

These rings are made of a tough material called Cartilage. They help to hold the tube open.

You can think of the trachea as a tube lined with C-shaped supporting rungs.

Diagram of trachea with cartilage rungs.


Although this would stop the tube from collapsing,

this would also mean that the tube would not

be able to expand. When we breathe in, the trachea must expand to

allow more air in.

Well, if a tube were lined with fixed circles of cartilage, it would have a fixed diameter…

Cartilage

Trachea


Therefore, a C-shaped piece of cartilage can change shape.


As well as being adapted on its outer surface, the trachea shows adaptations on its inner lining.

If we look closely at the inner surface of the trachea…

ciliated epithelial cells


The cells that line the wall of the trachea show two special adaptations.

produce a sticky liquid called mucus

tiny hairs called Cilia

Ciliated epithelial cells

We say the cells show specialisation. These specialised cells have a particular job to do.


Ciliated Cells

Mucus being made by the ciliated cells.

Microbes travelling down

the trachea within inhaled

air.

Microbes become stuck within the

mucus.

The presence of mucus and cilia on the lining of the trachea ensures that the air we breathe is

clean and free from disease.


Once the microbes are stuck in the mucus, the cilia move the mucus

upwards using a wafting action. The

mucus passes up to the top of the trachea

where it can either be swallowed or coughed

out of the body.Swallowed

Coughed


Eventually the trachea branches, dividing into two

smaller tubes called the left and right

Bronchi.(The singular of

bronchi is a bronchus) Right Left

Trachea

Don’t forget that in a picture of the human body, right becomes left and left becomes right. Check by holding up your right

hand in a mirror. The person staring back at you will be holding up their right hand.


Each Bronchus connects the trachea to a large air sac known as a Lung. You have two bronchi and therefore your body

has two lungs, a left and a right.

Trachea

Left Bronchi

Left Lung

Right Bronchi

Right Lung


Bronchiole

Cartilage

In reality, the lungs are different in shape. Here is a more accurate diagram.

Trachea

Right Bronchus

Location of the heart

Pleural Membrane

Right Lung


With air entering and leaving the lungs, they are going to increase and decrease in size on a regular basis.

When organs in the body increase in size, they will touch other

organs because of the lack of space.

This is a danger because living tissue is very delicate and when tissues rub against each other, friction could be generated.

Organ 2Organ 1

FRICTION

This friction could damage the tissue and kill cells. Therefore, a protective bag called the Pleural membrane surrounds the lungs,

which are likely to rub against other organs during the breathing

process.


A fluid is found within this bag, surrounding the lungs. This fluid lubricates the lining of the lungs and stops

friction being generated.

Plural Membrane

Lung

Fluid


Bronchi

These smaller branches are known as

bronchioles

Each Bronchus now starts branching to produce smaller and smaller tubes.

One bronchus gives rise to many bronchioles. The overall effect is similar to the branching of a tree from a central trunk.

This branching of the bronchi occurs within both lungs.


Down the trachea

Through each bronchus

And through all the bronchioles within

each lung

BUT WHAT HAPPENS NEXT?

Always remember

that the CO2

is moving in the opposite

direction!

Oxygen will pass


Actually, each air sac is found to be a

bundle of air sacs. Together, they are

known as an Alveolus.

We can look inside the alveolus to get some idea of why they are shaped the way they are.

The outside of the alveolus is covered with

tiny blood vessels.

Oxygen makes its way to special air sacs.


Here is a cross section:Oxygen (O2) gas passes

through here

This O2 is then able to dissolve in

a small moist lining

Lining of the alveolus


The O2 gas molecules

O2 O2

O2

O2

dissolve

dissolve

Moist lining

This moist lining also stops the alveolus from drying and cracking. It lubricates the insides of the air bag.


After the oxygen dissolves it also diffuses.

O2 O2O2O2

Cell lining of alveolus

Cell lining of

capillary

Blood

D I F F U S I O N

The Oxygen molecules must diffuse through both the lining of the alveolus and the lining of the blood capillary.

They are eventually picked up by red blood cells.


The bloodblood now carries this oxygen to the cells of the

body.

Right Lung

Left Lung

Blood vessel

Body cells

Blood

O2

O2


The movement of the oxygen from the blood to the cells also follows the law of diffusion.

Blood coming from

the lungs

Body cellBody cell

High concentration

Low concentration

It is highly concentrated

within the blood

Meanwhile the concentration is

low within the cell

Therefore the Oxygen passes into the body cells


Remember that the process of inhalation brings O2 into the body whilst exhalation removes CO2.

So, how does our breathing system enable us to do this.

Well, inhaling and exhaling are brought about by certain changes in the changes in the positionposition of our breathing system.

Let us look again at the general structure of this system.

Remember, the breathing system is found in the upper region of the

body. This is known as the thorax.


Picture of the respiratory

system

Ribs

Rib muscles

Right Lung

Diaphragm

Left Lung

Trachea

Right Bronchus

This system does not have a fixed shape. It has the ability to move, whilst remaining enclosed within the

protection of the ribcage.


This means that the rib cage must also be able to change position.

OBSERVATIONOBSERVATION

Take your hands and place them flat on your chest just above your hips on each side of

your body. Now breathe in and out very deeply. Whilst you do this, watch to see what

happens to your hands.

You should notice the following things…..


When you breathe in (inhale), your hands move upup and outwardsoutwards.

When you breathe out (exhale), your hands move downdown and inwards.inwards.

Let’s see why…. InhalingInhaling

When we inhale, our lungs fill with air.

As they fill, they become enlarged.

The ribs must then move upwards and outwards to make more room in the thorax.

The overall effect of this is that our chest expands.


Your diaphragm is also involved in the inhalation process. It’s location beneath the lungs means that it separates the thorax

from the abdomen.

It is a sheet of muscle that spans the width of the body.

Just before we inhale, it is found in a domedome shape.

As we inhale, it contracts and flattensflattens.

The result of this change in shape is a

change in the volume of the thorax.

Inhaling


As the volume of the thorax increases, the internal air pressure drops. This means that the air pressure outside the

lungs is greater than the air pressure inside the lungs.

•Diaphragm flattens

•Air pressure drops

•Thorax volume increases

•High air pressure outside

Low

High

•Low air pressure inside

•Air diffuses into the lungs


If these changes occur when we breathe in, the opposite must happen when we breathe out.

These changes can be summarised in the table below...

Feature Inhaling Exhaling

Diaphragmshape

Flat Domed

Ribs Up and out Down and in

Diaphragmmuscle

Contracted Relaxed

Rib Muscle Contracted Relaxed

Lungs Inflated Deflated


Click on the ‘Air Drawn in’ buttons to explore the animation.


Click on the ‘Passage of air’ buttons to explore the animation.



“A Load of hot air!”

The following activity will help you review your understanding of the structure of the breathing system.

InstructionsInstructions:

•There are 20 questions to answer

•The number in brackets tells you how many letters in the word.


Questions1 This is the toxic gas that is released when we breathe

out? (6, 7)2 When these contract and relax they move the rib-cage out

and in? (3, 7)3 The name for the minute air sacs that are covered with

blood vessels? (7)4 The area of the body where the lungs are found? (6)5 A protective structure surrounding the lungs (3, 4)6 The trachea branches into _________ (7), one going to

each lung.7 The circulatory system will take oxygen to the _______

(5) of the body.8 Directly beneath the lungs is a sheet of muscle known as

the ____________ . (9)

“A Load of hot air!”


9 The cavity through which we breathe and eat. (5)

10 The human breathing system contains two of these large spongy air bags. (5)

11 The other name for the wind-pipe? (7)

12 The name for the junction between the oesophagus and the wind-pipe? (7)

13 This is one of the dead-end sacs at the end of the bronchioles (8)

14 The left ________ (8) connects the left lung to the trachea.

15 The gas needed by the body to perform respiration? (6)

16 The diaphragm separates the breathing system from the __________.(7)


17 The area that connects the nose to the pharynx. (5, 6)

18 The main purpose of the breathing system is to generate _________. (6)

19 One of two openings of the breathing system located above the mouth. (7)

20 The name of the release of energy from food? (11)


“Don’t hold your breath!”

Pretending you are air!Pretending you are air!

List down the answers to questions 19, 17, 13, 12, 11, 10 and 6. Now re-order the words to represent a trip through the breathing system, beginning outside the body. You must also try to fit the bonusbonus word ‘bronchioles’ into your list.

ActivityActivity


When we breathe, we are doing so to fuel the process of ____________ , which is one of the characteristics of life. __________ is taken in and ________ __________ is removed in the process. The oxygen eventually leaves the breathing system and enters the circulatory system. This then transports the gas around the body to all the body ________ which can generate __________.

Use answers from questions 1, 7, 18, 15 and 20 to fill in the following explanation of the purpose of breathing oxygen into our bodies.

Where’s the air going?Where’s the air going?ActivityActivity


Words that mean the same thing.Words that mean the same thing.

Answer the following questions. Be careful, the spelling is essential!

1. What is the name of one tiny air sac?

2. Many tiny air sacs are known as ________?

3. What is the name of one branch of the trachea?

4. The name for the tubes that branch from the trachea are known as ___________?

ActivityActivity


When we breathe in, our lungs fill with air. Identify two ways our breathing system creates more room in the thorax for these inflated lungs.

The lungs have to move!The lungs have to move!

ActivityActivity


WordsearchWordsearch

E V V X W R Z R I B C A G E D T U W D I A P H R A G M P I Y E X Y B L D A O G C H L X S U N D M V B E N E R G Y O Z R O G U E I D C A M N K I F M S E S O C T H O R A X D E G T F C L B F U I U S N N T W R A L I U T S K J A Y O B Q I H E H H N J I L L R B V C L E S O X Y G E N C A R X Q A L V E O L U S M A H A R E S P I R A T I O N V P C E L L S M B R O N C H I S N D R O N L A E H C A R T J S M N N K P O O Q P P R Y T


Does size matter?


Which means what?


In and out but which way around?


The breathing system is designed to carry out certain functions. If we look at specific features of the system, we should be able to explain why they look the way they do.

Read each ‘feature’ (in red) statement and each ‘explanation’ (in blue) statement. Then try to drag the correct feature to the explanation.

e.g. small flexible flap, the epiglottis

covers the trachea when we swallow to stop the food passing into the lungs

ActivityActivity


Match the correct feature to the explanation.


Match the correct feature to the explanation.


Multiple choice questions


1. When we inhale, muscles between the ribs…

A relax causing the ribcage to move upwards.

B contract causing the ribcage to move downwards.

C relax causing the ribcage to move downwards.

D contract causing the ribcage to move upwards.


2. When we inhale the diaphragm muscles:

A relax and this causes the diaphragm to return to its domed position.

B contract and this causes the diaphragm to return to its domed position.

C contract and this causes the diaphragm to flatten.

D relax and this causes the diaphragm to flatten.


3. When inhaling, the movement of the ribcage and diaphragm together combine to cause the volume of the chest cavity to…

A increase.

B decrease.

C return to normal.

D stay the same.


4. The change in volume when inhaling causes the pressure inside the lungs to:

A increase.

B decrease.

C return to normal.

D stay the same.


5. We inhale when…

A the pressure in the lungs is lower than the air pressure outside the body.

B the pressures are equal.

C the pressures in the lungs is higher than the air pressure outside the body.

D when the pressure inside the lungs is greater than that inside the blood.


6. Which of the following adaptations make the exchange of gases across the lung surface effective…

A few, large alveoli with a massive surface area, a dry inner surface and close proximity to an extensive capillary network.

B many, large alveoli with a massive surface area, a moist inner surface and close proximity to an extensive capillary network.

C many, tiny alveoli with a massive surface area, a moist inner surface and close proximity to an extensive capillary network.

D few, tiny alveoli with a small surface area, a dry inner surface and close proximity to an extensive capillary network.

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© Boardworks Ltd 2003 The Breathing System Key Stage 4