Which of the following respiratory membrane layers is closest to air in the alveolus?

A) Alveolar epithelium
B) Alveolar basement membrane
C) Capillary basement membrane
D) Capillary endothelium
E) Alveolar fluid (with surfactant)

Respiratory Membrane

The thin barrier through which gas exchange occurs between the alveolar air and the blood in the lungs.

Alveolar Epithelium

The thin layer of cells that lines the alveoli (air sacs) in the lungs, playing a key role in the exchange of oxygen and carbon dioxide.