1. 6.4 Gas Exchange (Core)

2. Assessment Statements:
6.4.1 Distinguish between ventilation, respiration and gas exchange.
6.4.2 Explain the need for a ventilation system.
6.4.3 Describe the features of alveoli that adapt them to gas exchange.
6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli.
6.4.5 Explain the mechanism of ventilation of the lungs, in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

3. Ventilation The flow of air in and out of the alveoli
Two stages: inhalation and exhalation
Lungs are not muscular and cannot ventilate themselves
The thorax moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm.

4. Gas Exchange The diffusion of gases (oxygen and carbon dioxide)
Two sites for gas exchange:
Alveoli: Oxygen diffuses into the blood from the alveoli and carbon dioxide diffuses from the blood into the alveoli
Tissues: Oxygen diffuses from blood into the cells and carbon dioxide diffuses from cells to the blood

5. Gas Exchange in Alveoli

7. Cell Respiration
Aerobic respiration uses oxygen in the mitochondria and produces carbon dioxide
Anaerobic respiration does not use oxygen but still produces carbon dioxide

9. Why do we need a ventilation system?
To maintain a concentration gradient for diffusion
Air is constantly being refreshed in the lungs
keeping the concentration of oxygen high and carbon dioxide low
At the same time bllood is constantly carrying away oxygen and bringing new carbon dioxide
Both gases diffuse down their concentration gradient from high to low concentration

10. Watch the animation and summarise the process of ventilation

13. Features of alveoli for gas exchange
Large numbers of alveoli gives large surface area for gas exchange
Single layer of flattened cells in wall of alveoli
Short distance for diffusion of gases
Oxygen dissolves in thin film of moisture on inside of alveoli - this aids diffusion
Surrounded by dense network of capillaries

14. The Ventilation System
intercostal muscles
bronchi
ribs
heart
bronchioles
diaphragm
alveolus

15. Review