1. The Lungs
How are the lungs adapted to provide our bodies with all the oxygen we need?

2. Success Criteria
Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus.
Describe the features of the mammalian lung that adapt it to efficient gas exchange.
Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.

3. The structure of the thorax1. 6. 3. 7. 8. 4. 5. 9.
10.

4. The structure of the thorax
C-shaped cartilage
Trachea
Right lung
Left lung
Intercostal muscle
Rib
Bronchus
Bronchiolus
Diaphragm

5. Gaseous Exchange
Gaseous Exchange is the movement of gases by diffusion between an organism and its environment across a barrier such as the alveolus wall

6. The lungs are a large pair of inflatable structures lying in the chest cavity
Air can pass into the lungs through the nose and along the trachea, bronchi and bronchioles
Finally the air reaches tiny, air-filled sacs called alveoli. The walls of the alveoli are the surface where the exchange of gases takes place

7. Success Criteria
Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus.
Describe the features of the mammalian lung that adapt it to efficient gas exchange.
Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.

8. The lungs are protected by the ribs
The lungs are protected by the ribs. Movement of the ribs together with the action of the diaphragm (a layer or muscular tissue beneath the lungs) help to produce breathing movements (ventilation)

9. Inspiration and Expiration

11. Ventilation
The ribcage, intercostal muscles and diaphragm all work together to move air into and out of the lungs, where gas exchange occurs across the thin (single-celled) walls of the alveoli
Ventilation is a physical process, relying on the principle of Boyle’s Law – which state
“Pressure is inversely proportional to volume”
The mechanism can be illustrated using a bell jar model of the respiratory system – however, the model does not illustrate involvement of the rib cage and the intercostal muscles in ventilation
Breathing out
(expiration / exhalation)
Breathing in (inspiration / inhalation)
Internal intecostals contract in forced expiration

12. INSPIRATION EXPIRATION Diaphragm & external intercostals contract
Atmospheric pressure = 760 mmHg
Diaphragm & external intercostals contract
Rib cage raised (upwards and outwards)
Diaphragm lowered (becomes flatter)
Volume of chest cavity increases
Pressure in chest cavity drops to below
atmospheric pressure to 758 mmHg
Air moves into lungs from atmosphere
Active process
Diaphragm & external intercostals relax
Rib cage lowered
Diaphragm raised (dome shape) due to push
from abdominal organs
Volume of chest cavity decreases
Pressure in chest cavity increases to
above atmospheric pressure to763 mmHg
Air forced out of lungs into atmosphere
Aided by elastic recoil and abdominal organs Passive process

14. Inhaling (Inspiration) Exhaling (Expiration)
Volume of thorax
Diaphragm muscle
Diaphragm
Relaxes and resumes to dome shape
External intercostal muscles
Rib cage
Pressure in chest cavity
Decreases below atmospheric pressure
Movement of air

15. Inhaling (Inspiration) Exhaling (Expiration)
Volume of thorax
Increases
Decreases
Diaphragm muscle
Contracts
Relaxes
Diaphragm
Flattens and pushes digestive organs down
Relaxes and resumes to dome shape
External intercostal muscles
Contracts/expands
Rib cage
Upward and outward
Inward and downward
Pressure in chest cavity
Decreases below atmospheric pressure
Increases below atmospheric pressure
Movement of air
Into the lungs down pressure gradient
Air forced out of lungs

16. Exam question (5 marks)

18. Success Criteria
Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus.
Describe the features of the mammalian lung that adapt it to efficient gas exchange.
Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.

19. Gases pass both ways through the thin walls of the alveoli.
Oxygen passes from the air in the alveoli to the blood in the capillaries.
Carbon dioxide passes from the blood to the
air in the alveoli.

20. Task View the selection of lung slides Complete a lung dissection
Then answer the following questions as fully as you can.... (you can use Text book page 46 to help you)
State 3 ways in which the structure of the lungs allows efficient gas exchange (4).
Explain why the barrier to diffusion must be as thin as possible (1).
Describe how a steep diffusion gradient is achieved in the lungs (4).

21. Answers
State 3 ways in which the structure of the lungs allows efficient gas exchange (4). Large surface area (1) provides more space for molecules to pass through (1), plasma membranes surrounding the cytoplasm create a permeable barrier allowing diffusion of oxygen and carbon dioxide (1), alveolus wall is one cell thick creating a thin barrier for diffusion (1)

22. Answers
Explain why the barrier to diffusion must be as thin as possible (1). It reduces the distance gases have to diffuse (1)

23. Answers
Describe how a steep diffusion gradient is achieved in the lungs (4). Blood brings carbon dioxide from the tissues to the lungs ensuring the carbon dioxide concentration in the blood is higher than that of the air in the alveoli (1), it also carries oxygen away from the lungs ensuring that the concentration of oxygen in the blood is kept lower than air inside the alveoli (1), the movement of the lungs (ventilation) ensures there is a fresh supply of oxygen entering the lungs increasing the concentration of oxygen in the alveoli (1), carbon dioxide is also removed by ventilation ensuring that the concentration in the alveoli is lower than that of the blood (1)

24. How do the alveoli decrease the diffusion distance?

25. How do the alveoli decrease the diffusion distance?
Alveolus and capillary are 1 cell thick
Alveolus and capillary are squamous epithelium.
Total barrier thickness = 1 um
Capillaries in close contact.
Capillaries are narrow so RBC squeeze through. Closer to alveolus and slows down movement.

26. Think! Read the sentence below... Is it correct? If not, why not?
Alveoli have thin cell walls- this decreases the distance that gases have to travel and speeds up rates of diffusion
Alveoli have thin cell walls- this decreases the distance that gases have to travel and speeds up rates of diffusion
Alveoli have thin walls- their walls are one cell thick!

27. Success Criteria
Describe the features of an efficient exchange surface with reference to diffusion of oxygen and carbon dioxide across an alveolus.
Describe the features of the mammalian lung that adapt it to efficient gas exchange.
Outline the mechanism of breathing (inspiration and expiration) in mammals with reference to the function of the rib cage, intercostal muscles and diaphragm.