1. 4.2 The mechanism of breathing
Lungs and lung disease
4.2 The mechanism of breathing

2. Learning outcomes Students should understand the following:
The mechanism of breathing.
Pulmonary ventilation as the product of tidal volume and ventilation rate.

3. Spot the difference! Atmospheric pressure 760mm Hg
Intra- alveolar pressure 758mm Hg
Atmospheric pressure 760mm Hg
Intra- alveolar pressure 760mm Hg

4. Breathing in and out Breathing in Breathing out
1. Diaphragm contracts and moves downward.
1. Ribcage moves down and inwards.
2. Air moves into the lungs.
2. Pressure in lungs increases.
3. Intercostal muscles contract.
3. Diaphragm relaxes and moves upwards.
4. Pressure in lungs decreases.
4. Intercostal muscles relax.
5. Ribcage moves up and outwards.
5. Air moves out of the lungs.

5. Breathing in and out Breathing in Breathing out
1. Intercostal muscles contract.
1. Intercostal muscles relax.
2. Ribcage moves up and outwards.
2. Ribcage moves down and inwards.
3. Diaphragm contracts and moves downward.
3. Diaphragm relaxes and moves upwards.
4. Pressure in lungs decreases.
4. Pressure in lungs increases.
5. Air moves into the lungs.
5. Air moves out of the lungs.

6. The 2 breathing processes
The body separates the procedure of breathing in and breathing out.
By separating these two processes, the body can concentrate on the two tasks in turn.
Breathing in is one process and is known as…
Breathing out is a separate process and is known as…
Inhalation
(When we breathe in we inhale)
Exhalation
(When we breathe out we exhale)

7. Breathtaking features
The breathing system does not have a fixed shape.
ribs
rib muscles
Right Lung
diaphragm
Left Lung
trachea
right bronchus
It has the ability to move, whilst remaining enclosed within the protection of the ribcage.

8. A mobile ribcage?
This means that the rib cage must also be able to change position.
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…..

9. Take a breath
When you breathe in (inhale), your hands move up and outwards.
When you breathe out (exhale), your hands move down and inwards.

10. Inhaling: chest expansion
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.

11. Pressure changes
The pressure changes in the lungs are brought about by the movement of 2 sets of muscles:
The diaphragm – a sheet of muscle that separates the thorax and the abdomen.
The intercostal muscles:
Internal intercostal muscles – contraction leads to expiration
External intercostal muscles – contraction leads to inspiration

12. The diaphragm
Your diaphragm is located beneath the lungs, which means that it separates the thorax from the abdomen.
It is a sheet of muscle that spans the width of the body.
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

13. Pressure regulation
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.
Low
High
High air pressure outside
Low air pressure inside
Air diffuses into the lungs
Diaphragm flattens
Air pressure drops
Thorax volume increases

16. During exercise
Inspiration is always an active process. When the body is at rest expiration is passive ( the diaphragm muscles relax and the elastic recoil of the lungs and chest wall return the thorax to it’s original shape.) During exercise expiration is boosted by contraction of the internal intercostal muscles

17. Key definitions
Tidal Volume - The volume of air inhaled and exhaled at each breath, this is normally equivalent to only 10% of the total 5L volume of the trachea and lungs.
Residual Volume - the amount of air still remaining in the lungs after the most forceful expiration.
Vital Capacity - the maximum amount of air that can be exhaled after a maximum inhalation.
Training can increase the strength of the diaphragm and intercostal muscles and can thus raise the vital capacity and hence improve performance.

18. Breathing (Lung Volume) Spirometer Trace
Work Out:
Tidal Volume
Vital Capacity
Residual Volume

19. Breathing (Lung Volume) Spirometer Trace
Work Out:
Tidal Volume
Vital Capacity
Residual Volume

21. Question 1 p86

22. Pulmonary ventilation
This is the total volume of air that is moved into the lungs during one minute. To calculate it we can multiply 2 factors together:
Tidal volume – the volume of air normally taken in in each breath when the body is at rest (normally 0.5dm3).
Ventilation rate – the number of breaths taken in one minute (normally breaths).
Pulmonary Ventilation = Tidal Volume x Ventilation Rate
(dm3min-1) (dm3) (min-1)

23. Summary questions
1000 cm3 = 1 dm3

24. Q2 p86

25. Learning outcomes Students should understand the following:
The mechanism of breathing.
Pulmonary ventilation as the product of tidal volume and ventilation rate.