Gas Exchange Surfaces

• Within the lungs, alveoli provide a large surface area for exchange of gases between air and the blood
• Some of the features of alveoli include - large surface area, numerous capillaries surrounding alveoli and thin walls of alveoli

The body's demand for oxygen is enormous, so diffusion across the alveolar wall needs to be rapid. The rate of diffusion is dependent on three properties of gas exchange surfaces:

1. Surface Area - rate of diffusion is directly proportional to the SA, as it increases the rate of diffusion does too
2. Concentration Gradient - rate of diffusion directly proportional to difference in concentration across the gas exchange surface, greater the concentration the faster the diffusion
3. Thickness of Gas Exchange Surface - rate of diffusion is inversely proportional to thickness of gas exchange surface, the thicker the surface the slower the diffusion

How Sticky Mucus Might Affect Gas Exchange:

• Sticky mucus layer in the bronchioles of a CF patient blocks these narrow airways, preventing ventilation of the alveoli below the blockage
• This reduces the number of alveoli providing surface area for gas exchange - blockages are more likely at the narrow ends of the airways
• These blockages will often let air in but not back out when exhaling, causing inflation of the alveoli, damaging elasticity of the lungs
• People with CF find it difficult to take part in physical exercise because their gas exchange system can't deliver enough oxygen to their muscles