The Alveolar Epithelium (AQA AS Biology): Revision Note

The alveolar epithelium

• The alveolar epithelium functions as an exchange surface

  • Oxygen and carbon dioxide are exchanged between the alveoli and the capillaries in the process of diffusion

• The features of the alveolar epithelium make it an extremely effective exchange surface; it has:

  • a large surface area

    • The lungs contain many alveoli, increasing the surface area available for oxygen and carbon dioxide to diffuse

  • thin walls

    • The walls of the alveoli are only one cell thick

    • Alveolar epithelium cells are flattened in shape

    • Gases have a very short diffusion distance

  • a steep concentration gradient

    • The constant flow of blood through capillaries that are immediately adjacent to the alveolar epithelium means that oxygenated blood is carried away from the alveoli very quickly

    • This maintains the concentration gradient necessary for diffusion of oxygen to occur