Alveolar basement membrane in the context of "Blood–air barrier"

The blood–air barrier or air–blood barrier, (alveolar–capillary barrier or membrane) exists in the gas exchanging region of the lungs. It exists to prevent air bubbles from forming in the blood, and from blood entering the alveoli. It is formed by the type I epithelial lining cells of the alveolar wall, the endothelial cells of the capillaries and the fused basement membrane between, forming the alveolar basement membrane. The barrier is permeable to molecular oxygen, carbon dioxide, carbon monoxide and many other gases.