The blood-air barrier consists of all of the following except:
Alveolar pores connect neighboring alveoli and func­tion in equalizing pressure in the alveoli and enable collateral circulation of air. They do not constitute part of the blood-air barrier.
Alveolar pores
A layer of surfactant
Type I alveolar cell cytoplasm
Fused basal lamina of alveolar and endothelial cells