1. Respiratory System Lesson Objectives: Recap on O2 journey
Characteristics of alveoli
Function of alveoli

2. Alveoli How do we breathe?
Lungs take in oxygen & breathe out carbon dioxide
This gas exchange takes place in the alveoli of the lungs.

4. Characteristics of Alveoli
Each alveolus is smaller than a grain of salt.
The walls are thin and moist
Surrounded by a capillary network (tiny blood vessels)

5. Characteristics of Alveoli
Why do you think there are millions of tiny ones rather than one big one?
Surface area – the exchange of gases is far more efficient if there is a greater surface area for it to diffuse through.