1. The mechanism of breathing
02/11/11
The mechanism of breathing
WAL:
how the parts of the respiratory system work together to enable breathing.
All
Most
Some
What is meant by pulmonary ventilation and how is it calculated?
How is air moved in and out of the lungs?
What features of the gas-exchange system are responsible for the pressure changes in the lungs?

2. Key words & Definitions
Ventilation - Scientific term for “breathing” – where air is constantly moving in and out of the lungs.
Inspiration - Also known as “inhalation”, occurs when air pressure in the atmosphere is greater than that of the lungs; forcing air into the alveoli.
Expiration - Also known as “exhalation”, occurs when air pressure in the lungs is greater than that in the atmosphere; forcing air out of the alveoli.
10min into lesson – students copy definitions down

3. How does ventilation happen?
Ventilation requires pressure changes to occur in the lungs, so that air can be forced in an out of the alveoli.
The pressure changes are brought about by the movement of two sets of muscles....

4. How does ventilation happen?
The diaphragm, which is a sheet of muscle that separates the thorax (chest) from the abdomen.
The intercostal muscles which lie between the ribs. There are two sets of intercostal muscles....

5. The intercostal muscles – an antagonistic pair
The internal intercostal muscles, whose contraction leads to expiration.
The external intercostal muscles, whose contraction leads to inspiration.

6. Ventilation
15min into lesson

7. Ventilation
15min into lesson

8. Ventilation
15min into lesson

9. Ventilation
15min into lesson

10. Task – 15 minutes Draw a table like the one below....
Fill in what happens to the things on the left (i.e diaphragm, air pressure in lungs...) during inspiration and expiration.
Use your textbook to help you.
Inspiration
Expiration
External intercostal muscles
Internal intercostal muscles
Diaphragm
Air pressure in lungs
Air movement along pressure gradient
Lung volume

11. Answers, please! Inspiration Expiration External intercostal muscles
Internal intercostal muscles
Diaphragm
Air pressure in lungs
Air movement along pressure gradient
Lung volume

12. Answers, please! Inspiration Expiration External intercostal muscles
Contract – pulling ribs upwards and outwards.
Relax – permitting rib cage to move downwards and outwards.
Internal intercostal muscles
Are relaxed.
Contract – moving the ribs downwards and decreasing the volume of the thorax.
Diaphragm
Contracts – moves downwards from domed position.
Relaxes – elasticity returns to domed position,
Air pressure in lungs
Decreases
Increases
Air movement along pressure gradient
Into lungs
Out of lungs
Lung volume
30min into lesson

13. Back to the lungs!
Demo the lungs with the bicycle pump. Ask students the key question “The lungs have taken in quite a significant amount of air. But how could we work out exactly how much air is taken into the lungs?” – to introduce the idea of pulmonary ventilation.

14. Pulmonary Ventilation
Pulmonary ventilation is the total volume of air that is moved into the lungs during one minute (dm3min-1). To calculate it we multiply together two factors....

15. Pulmonary Ventilation
Tidal volume – the volume of air normal taken at each breath when the body is at rest. This is usually around 0.5dm3 (half a litre).
Ventilation (breathing) rate – i.e the number of breaths taken in one minute. This is normally in a healthy adult.

16. Pulmonary Ventilation – to summarise
= tidal volume x ventilation rate
ventilation
(dm3min-1) (dm3) (min-1)

17. But how to we measure tidal volume?
We can use a spirometer
40min into lesson

18. Demonstrate your understanding
Complete summary questions 1 to 3 on page 145 in your textbook.
You have 10 minutes.

19. Answers, please
50min into lesson

20. Homework – due 2nd March
Complete the exam questions