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. While the red blood vessel is our blood vessel called the pulmonary vein. That brings oxygenated blood from each individual alveolis and to the heart of our body, specifically to the left atrium of our body. So remember, the pulmonary artery carries the oxygenated blood away from the heart and to the lungs while the pulmonary vein carries oxygenated blood away from the lungs and to our heart.