So we have the pulmonary arterio, we have the pulmonary capillary, and we have the pulmonary venue. So our deoxygenated blood essentially travels along the pulmonary terio until it gets to our capillary, which is this section right here. Now, deoxygenated blood has a relatively high concentration of carbon dioxide and a relatively low concentration of oxygen compared to the concentrations of these molecules, gas molecules, inside the alveolar space. So this region here is region number eight, the alveolar space. Now, within the alveolar space, we have a partial pressure of oxygen equaling to 105 mercury, while the partial pressure due to our carbon dioxide molecules, that is 40 mercury, now, inside the lumen of our pulmonary arterial, these are the concentrations, these are the partial pressures of these same gas molecules. Notice the oxygen is 40 mercury, which is less than inside the alveolar space, while the carbon dioxide has a higher concentration, 45 mercury, inside the lumen of the arterial compared to our alveolar space.