Diffusion in the lungs

• In the lungs oxygen diffuses from a region of high concentration in the air to a region of low concentration in the blood , the oxygen diffuses down its concentration gradient
• Rate of diffusion increased by the milllions of alveoli to increase the surface area over which the diffusion is occurring and a good blood supply ( fine network of tiny capillaries )
• Rate of diffusion increased by there being a steep concentration gradient between the air and the blood , the blood arriving at the lungs is low in oxygen , as the respiring tissues have used it up so diffusion is rapid
• Gradient maintained in the lungs by ventilation - new oxygen rich , carbon dioxide poor air is constantly replacing the old air
• Rate of diffusion increased by small distance between the air and the blood ; alveoli and blood capillaries are very close to each other and each is only one cell thick , provides a short diffusion path , gases can easily dissolve in the moist surfaces