1. Mammalian
Gas Exchange

2. The Human Respiratory System
Trachea
Cartilage (C-shaped rings)
Bronchiole
Rib Bone
Bronchus (Plural = Bronchi)
Lung
External intercostal muscle
Alveoli (singular = an alveolus)
Internal intercostal muscle
Diaphragm

3. A closer look at the alveoli

4. Alveoli and capillaries

5. Oxygen diffusing into rbc
Endothelial cell
From Pulmonary
artery
Red blood cell (rbc)
Oxygen diffusing into rbc
Surfactant
Epithelial cell of alveolus
Carbon dioxide diffusing into alveolus

6. Small section through lung tissue
Alveolus
Blood capillary

7. EM of alveoli

8. Cross-section through alveoli walls

9. The diffusion pathway alveolus capillary Fluid and surfactant
epithelium of alveolus
Interstitial space
Diffusion pathway of CO2
endothelium of capillary
Diffusion barrier
Diffusion pathway of O2
Red blood cell
capillary

10. 1) Do TASK on base of p4 HB: List all the structures that the air passes through on its journey from the nose to the capillaries surrounding the lungs. 2) Do TASK on bottom of p5 HB including a copy of FICK’S LAW OF DIFFUSION (see p78-79 Textbook): 3) Think of a great definition of diffusion!

11. Essential features of a gas exchange surface:
Large surface area to volume ratio.
Thin, so there is a short diffusion pathway.
The maintenance of a steep concentration gradient to allow a fast rate of diffusion.
Partially permeable.
Add a bit more to explain these points into the table on HB p5. Use textbook p79 to help).

12. The lungs as a good gas exchange surface
Large surface area
Provided by many alveoli
(approx 600 million in a human)
Short diffusion pathway
Capillaries surround the alveoli
Alveolar epithelium and capillaries are each only one cell thick
Steep concentration gradient
Ventilation brings in fresh air and keeps the oxygen concentration high in the alveoli
Blood flowing through the capillaries removes oxygen and keeps the concentration low here
END.

13. Diffusion
Gas Exchange relies on the diffusion of oxygen and carbon dioxide.
What do you understand by diffusion?
What factors might increase the rate of diffusion?
The movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient.
1. Large surface area to volume ratio. 2. Steep concentration gradient. 3.Short diffusion pathway. 4. Small molecules. 5. Permeable surface.

14. Steep Concentration Gradient Short Diffusion Pathway
Adaptation
Large Surface Area
Steep Concentration Gradient
Short Diffusion Pathway
How are the lungs adapted to have a short diffusion pathway?
How are the lungs adapted to maintain a steep concentration gradient?
How are the lungs adapted to give a large surface area to volume ratio?
A vast number of very small alveoli provide a large surface area to volume ratio.
Alveoli are covered with a network of capillaries. Ventilation of lungs.
The walls of the alveoli and capillaries are very thin (each is only a single layer of epithelial cells.
This allows rapid diffusion of gases to occur, as the diffusion distance is kept to a minimum.
This increases the rate of diffusion, as more O2 + CO2 can diffuse at the same time
How does this help to maintain a steep concentration gradient?
Why is a large surface area an advantage?
Blood moves on oxygen quickly to maintain a lower concentration of O2 in the alveolar blood than in the alveolar air.
Why is this an advantage in diffusion?

15. So what does this tell you?1 2 1 1 2 2 3
So what does this tell you? 3 3
Cube Dimensions
1 x 1 x 1
2 x 2 x 2
3 x 3 x 3
Surface area 6 24 54
Volume 1 8 27
Surface area : volume ratio
6:1
3:1
2:1

16. larger
Smaller organisms have a ________ surface area : volume ratio than bigger organisms.
This means that to be more efficient, larger organisms need a means to increase their surface area for their gas exchange e.g. by having lungs / gills / tracheoles (in insects).

17. Extra task (if time allows)
Now do the summary questions on p79