In alveoli of the lungs, the air at the site of gas exchange,

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In alveoli of the lungs, the air at the site of gas exchange, is separated from the blood by

1. alveolar epithelium only
2. alveolar epithelium and capillary endothelium
3. alveolar epithelium, capillary endothelium and tunica adventitia
4. alveolar epithelium, capillary endothelium, a thin layer of tunica media and tunica adventitia

Correct Option: B

Alveoli are the site of respiratory exchange of gases. Oxygen from the alveolar air diffuses through the alveolar epithelium and the capillary endothelium into the capillary blood, and carbon dioxide diffuses in the opposite direction.