And the space inside each one of these tiny alveoli looks something like this. That's the alveolar space. It's not the same as the alveolar sack space, but they are connected to one another. And so the concentration of gas molecules inside the alveolar sack space number seven and the alveolar space number eight is exactly the same. Now before we actually take a look at the structure of the actual alveolis, let's discuss what this blue section is and what the red section is. So this blue section is our blood vessel, the pulmonary artery, that actually brings deoxygenated blood from the heart to our lungs.