Now, within the capillary we have exchange taking place. Oxygen goes into the capillary and our carbon dioxide leaves the capillaries and goes into region number eight. And then our oxygenated blood travels via this blood vessel, number six, which is our pulmonary Venuel. It's a very small type of pulmonary vein. Now let's take a look at the actual membrane within which we have this diffusion of oxygen and carbon dioxide taking place. So notice we have two important types of cells within the alveolis.