Consists of bronchial capillaries, basal laminas and type 1 alveolar cells

Occurs at the terminal bronchiolar epithelium 

Consists of pulmonary vessels and type II alveolar epithelial cells

Consists of pulmonary capillary endothelium, fused basal laminas and type 1 alveolar cells

Occurs at the visceral pleura only, which is the deepest part of the conducting airway