Now, by the time the blood actually ends up within our lumen of the pulmonary Venuel, the concentration of carbon dioxide and oxygen will be the same inside the lumen as inside our alveolar space. And that's exactly why the diffusion of these two gas molecules essentially stops. And then our pulmonary Venuel connects with larger pulmonary arteries and that carry the oxygenated blood into the left atrium of our heart. So, once again, the deoxygenated blood brought by the pulmonary arteriol contains a relatively low partial pressure for oxygen and a relatively high partial pressure for carbon dioxide compared to the space inside our alveolus. Therefore, due to this pressure difference, due to the existence of this pressure gradient, oxygen will diffuse into the capillary and carbon dioxide will diffuse out of the capillary, down their pressure gradient. And this diffusion will continue until our partial pressure, the partial concentration or the partial pressure for oxygen is the same on the inside of the blood vessel as our inside space, the space inside our alveolar.