1. Gas Exchange

2. Types of gaseous exchange
External respiration (pulmonary respiration)
Gaseous exchange between the lungs and the blood. Blood gains oxygen and looses carbondioxide.
Internal respiration (tissue respiration)
Gaseous exchange between the blood and tissue cells. In internal respiration the blood looses oxygen and gains carbondioxide.

3. Airways leading to the Alveoli

4. Gas Exchange in the Alveoli

5. The exchange of Carbon Dioxide and Oxygen in the Alveoli

6. The Diffusion Pathway

7. The Diffusion Pathway A Large Surface Area A Small Diffusion Pathway
A Large Difference in Concentration

8. The percentage of gases in inspired, expired and alveolar air
Oxygen/%
Carbon Dioxide/%
Inspired air 21
0.04
Alveolar air 13 5
Expired air 16
4 – 4.5

9. Fick’s Law The rate of diffusion is proportional to:
Surface area x difference in concentration
Thickness of surface
Using Fick’s Law, explain how the Alveoli are an ideal site for gas exchange
The surface area is large and the difference in concentration is maintained by the flow of blood in the capillary network surrounding the alveoli. The surface is thin due to the epithelium of the alveoli and of the capillary being one cell thick and the red blood cell being close to the surface of the vessel.

10. The Breathing Mechanism
Intercostal muscles shorten

11. The Breathing Mechanism
Inspiration
External Intercostal Muscles and Diaphragm contract
The intercostal muscles shorten causing the rib cage to move up and out
The Diaphragm flattens and pulls downward
The Volume of the Thoracic Cavity ____________
This causes the air pressure to _______
As a result air is sucked into the lungs
decreases
fall

12. The Breathing Mechanism
Expiration
External Intercostal Muscles and Diaphragm relax
The intercostal muscles lengthen causing the rib cage to move down and in
The Diaphragm returns to its original dome shape
The Volume of the Thoracic Cavity __
This causes the air pressure to _______
As a result air is pushed out of the lungs
decreases
increase

13. During Exercise
During active exercise the Internal Intercostal muscles contract and forcibly lower the rib cage, expelling more air from the lungs, making room for a greater volume of air in each inspiration.

14. Control of Breathing
More Messages sent down ‘Phrenic Nerve’ to Intercostal muscles
Fewer messages sent down ‘Phrenic Nerve’ to Intercostal muscles