So we have this connecting point, this region here that connects number eight, the alveolar space, to number seven, the alveolar sack space. And because we have this direct connection, the concentration of our air molecules inside eight is the same as inside seven, which is the same as actually no, it's not the same. So in seven and eight we have the same exact concentration of gas molecules. Now notice that around the entire alveolis we basically have the system of blood vessels. So this blood vessel is our pulmonary arteriol. That brings deoxygenated blood and it loops around the entire alveolis until it gets to this section.