There are many alveoli within the lungs, resulting in a large surface area across which diffusion can occur
Short Diffusion Distance
Alveoli walls and capillary walls are one cell thick, reducing the diffusion pathway for gases
The capillary vessels are located directly next to the alveoli to minimise the diffusion pathway
Many Capillaries
This means that the alveoli have a good blood supply, maintaining oxygen and carbon dioxide concentration gradients
The blood arriving at the alveoli is high in carbon dioxide in comparison to the alveoli, so carbon dioxide diffuses out of the blood and into the alveoli
The blood is low in oxygen in comparison to the alveoli, so oxygen diffuses into the blood from the alveoli
High Oxygen Concentration
The process of ventilation ensures that the air in the alveoli always contains a higher concentration of oxygen than the blood; this means that oxygen diffuses into the blood
Layer of Moisture
Gases in the air dissolve in this layer on the surface of the alveoli, aiding diffusion
