Changes in the Partial Pressures of Oxygen and Carbon Dioxide
1. Oxygen diffuses into the blood and carbon dioxide diffuses into the alveoli because of differences in partial pressures.

2. As a result of diffusion, the PoÒ in the blood  is equal to the PoÒ in the alveoli and the PcoÒ in the blood is equal to the PcoÒ in the alveoli.

3. The PoÒ of blood in the pulmonary veins is less than in the pulmonary capillaries because of mixing with shunted blood.

4. Oxygen diffuses into the tissue and carbon dioxide diffuses out of the tissue because of differences in partial pressures.

5. As a result of diffusion, the PoÒ in the blood is equal to the PoÒ in the tissue and the PcoÒ in the blood is equal to the PcoÒ in the tissue.