1. The Breathing System

2. Humans breathe to ensure that oxygen enters the body
Humans breathe to ensure that oxygen enters the body
and that carbon dioxide leaves the body.
Oxygen (O2)
Carbon Dioxide (CO2)

3. But why do we need to do this?
When something burns, heat and light energy is released.
This process will produce energy if there are 2 main ingredients.
combustion
FUEL + OXYGEN CARBON + WATER
DIOXIDE
If these two and heat are all present then the fuel and oxygen will react. This reaction is called COMBUSTION.

4. But why do we need to do this?
The body breaks down food into a form which can be carried around the body. This substance is called GLUCOSE.
Glucose contains energy
Glucose “burns” in oxygen. This reaction releases energy. Some of this energy is released as heat while the rest is used by the cells.

5. We can now write out the full equation for RESPIRATION.
What is respiration?
RESPIRATION is the process which releases energy from food. This is NOT the same as breathing.
We can now write out the full equation for RESPIRATION.
FOOD (GLUCOSE)
OXYGEN +
from digestive system
from breathing system
WATER
CARBON DIOXIDE +
ENERGY
USEFUL!
waste product exhaled
Combustion is different because it is NOT a controlled reaction. Respiration IS a controlled reaction which SLOWLY releases energy from food in the CELLS.

6. Red blood cells carry oxygen, and the plasma in the blood carries dissolved food to ALL the cells in the body.

7. The breathing system
Let us now look at the structure of the breathing system.
The human body can be divided into three regions.
THORAX
ABDOMEN
HEAD
The breathing system is found in the thorax.

8. The body separates the process of breathing in and breathing 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.

9. There would be no time for anything else.
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.

10. 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.
Nasal cavity
Nostril
Mouth
Oral Cavity
It does not matter through which opening the air enters because the oral and nasal cavities are connected.

11. 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).

12. You may be wondering why they are C-shaped and not full circles.
You can think of the trachea as a tube lined with C-shaped supporting rungs.
These rings are made of a tough material called Cartilage. They help to hold the tube open.
Diagram of trachea with cartilage rungs.
You may be wondering why they are C-shaped and not full circles.

13. (The singular of bronchi is a bronchus)
Eventually the trachea branches, dividing into two smaller tubes called the left and right Bronchi.
(The singular of bronchi is a bronchus)
Trachea
Right
Left
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.

14. 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
Right Bronchi
Left Bronchi
Right Lung
Left Lung

15. In reality, the lungs are different in shape.
Here is a more accurate diagram.
Right Lung
Trachea
Cartilage
Right Bronchus
Pleural Membrane
Location of the heart
Bronchiole

16. 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.
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.
Organ 2
Organ 1
FRICTION

17. A fluid is found within this bag, surrounding the lungs
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

18. These smaller branches are known as bronchioles
Each Bronchus now starts branching to produce smaller and smaller tubes.
Bronchi
These smaller branches are known as bronchioles
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.

19. BUT WHAT HAPPENS NEXT? Oxygen will pass Down the trachea
Through each bronchus
Always remember that the CO2 is moving in the opposite direction!
And through all the bronchioles within each lung
BUT WHAT HAPPENS NEXT?

20. The outside of the alveolus is covered with tiny blood vessels.
Oxygen makes its way to special air sacs.
Actually, each air sac is found to be a bundle of air sacs. Together, they are known as an Alveolus.
The outside of the alveolus is covered with tiny blood vessels.
We can look inside the alveolus to get some idea of why they are shaped the way they are.

21. Here is a cross section: Oxygen (O2) gas passes through here
Lining of the alveolus
This O2 is then able to dissolve in a small moist lining

22. 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.

23. D I F F U S I O N After the oxygen dissolves it also diffuses. O2 O2
Cell lining of alveolus O2 O2 O2 O2
D I F F U S I O N
Cell lining of capillary
Blood
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.

24. The blood now carries this oxygen to the cells of the body.
Right Lung
Left Lung
Blood vessel O2
Body cells O2
Blood

25. It is highly concentrated within the blood
The movement of the oxygen from the blood to the cells also follows the law of diffusion.
Blood coming from the lungs
It is highly concentrated within the blood
High concentration
Low concentration
Meanwhile the concentration is low within the cell
Body cell
Therefore the Oxygen passes into the body cells

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

27. Picture of the respiratory system
Trachea
Ribs
Rib muscles
Right Bronchus
Diaphragm
Right Lung
Left Lung
This system does not have a fixed shape. It has the ability to move, whilst remaining enclosed within the protection of the ribcage.

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

29. When you breathe in (inhale), your hands move up and outwards.
When you breathe out (exhale), your hands move down and inwards.
Inhaling
Let’s see why….
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.

30. It is a sheet of muscle that spans the width of the body.
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 dome shape.
As we inhale, it contracts and flattens.
The result of this change in shape is a change in the volume of the thorax.
Inhaling

31. As the volume of the thorax increases, the internal air pressure drops
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.
High
Low
Diaphragm flattens
High air pressure outside
Thorax volume increases
Low air pressure inside
Air pressure drops
Air diffuses into the lungs

32. These changes can be summarised in the table below...
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
Diaphragm
Flat
Domed
shape
Ribs
Up and out
Down and in
Diaphragm
Contracted
Relaxed
muscle
Rib Muscle
Contracted
Relaxed
Lungs
Inflated
Deflated

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

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

36. “A Load of hot air!”
The following activity will help you review your understanding of the structure of the breathing system.
Instructions:
There are 20 questions to answer
The number in brackets tells you how many letters in the word.

37. “A Load of hot air!” Questions
1 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)

38. 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)

39. 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)

40. “Don’t hold your breath!”
Activity
“Don’t hold your breath!”
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 bonus word ‘bronchioles’ into your list.

41. Activity
Where’s the air going?
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.
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 __________.

42. Words that mean the same thing.
Activity
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 ___________?

43. Activity
The lungs have to move!
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.

44. Wordsearch

45. Does size matter?

46. Which means what?

47. In and out but which way around?

48. e.g. small flexible flap, the epiglottis
Activity
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.
covers the trachea when we swallow to stop the food passing into the lungs
e.g. small flexible flap, the epiglottis

49. Match the correct feature to the explanation.

50. Match the correct feature to the explanation.

51. Multiple choice questions

52. 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.

53. 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.

54. 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.

55. 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.

56. 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.

57. 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.