Question

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

• A. Alveolar epithelium only
• B. Alveolar epithelium and capillary endothelium
• C. Alveolar epithelium, capillary endothelium and tunica adventitia
• D. Alveolar epithelium, capillary endothelium, a thin layer of tunica media and tunica adventitia

Answer 1

The correct option is B Alveolar epithelium and capillary endothelium

Alveoli are small airbags present in the lungs. These are the site of the gas exchange. The oxygen and carbon dioxide gas are separated from the blood by alveolar epithelium and capillary endothelium. Oxygen from the alveoli diffuses through the alveolar epithelium and the capillary endothelium into the blood capillary. Similarly, carbon dioxide from the blood capillary diffuses through the capillary endothelium and the alveolar epithelium into the alveoli. Thus, the correct answer is 'Alveolar epithelium and capillary endothelium.'