Oxygen is critical for survival, and without lungs, it is impossible for that life-saving gas to enter the human body (Hsia et al., 2016). When the lungs are filled with fresh air, oxygen diffuses through the epithelium into blood vessels. To make this process more efficient, evolution has increased the surface of the lung. If you add up the area of the alveoli, you will get a surface of approximately 100 square meters. This enhances blood oxygenation in the lungs.