Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs?

The air that is breathed in passes down the trachea, the bronchi and bronchioles before reaching the alveoli. Oxygen is able to diffuse across the walls of the alveoli and the pulmonary capillaries into the blood due to several different factors. There is a large concentration gradient of oxygen from the alveoli to the pulmonary capillaries increasing the rate of diffusion. The diffusion pathway is also very short as the alveolar epithelium and the epithelium lining the pulmonary capillaries are each only one cell thick. Furthermore, the alveoli and the pulmonary capillaries have a very large surface area. These are the three components of Fick's principle that correlate with the rate of diffusion.