1. Requirements of a Gas Exchange System Mammals

2. Large Surface Area  Alveoli allow a surface area 40x that of the body

3. Moist - Thin Surface  Alveoli are lined with surfactant (prevents them collapsing on each other)  Alveoli are very thin walled (one cell thick)

4. Concentration Gradient  In order for diffusion of gases to occur a concentration gradient is maintained.  Achieved through the breathing process  Oxygen moves from high concentration in lungs to low concentration in blood  Carbon dioxide moves from high concentration in blood to low concentration in lungs

5. transport system  Capillaries containing RBC’s for movement of gases throughout the body

6. GE in relation to environment  Mammalian systems allow survival in many habitats (water, desert, mountains)  Mammals can be extreme in size or tiny (elephant and mouse)  Lungs are protected by ribs  Lungs are kept moist due to their structure  GE system can increase/decrease according to demand (breathing rate)