In which part of the lungs does respiration (gas exchange) primarily occur?

In which part of the lungs does respiration (gas exchange) primarily occur?

• A. Alveoli
• B. Capillaries
• C. Bronchi
• D. Trachea

Answer: (A)

Gas exchange happens across the thin walls of the alveoli, the tiny air sacs at the ends of the airways, where a vast network of capillaries surrounds each one. The alveolar walls and the capillary walls form the respiratory membrane, allowing oxygen to diffuse from the air inside the alveolus into the blood and carbon dioxide to diffuse from the blood into the alveolar air to be expelled. Alveoli provide an immense surface area and very thin barriers, which makes diffusion efficient. The bronchi and trachea are the airways that conduct air but do not participate in gas exchange, while capillaries are the blood vessels involved in transporting gases, with the actual exchange occurring across the alveolar–capillary membrane. So the primary site of respiration in the lungs is the alveoli.

Gas exchange happens across the thin walls of the alveoli, the tiny air sacs at the ends of the airways, where a vast network of capillaries surrounds each one. The alveolar walls and the capillary walls form the respiratory membrane, allowing oxygen to diffuse from the air inside the alveolus into the blood and carbon dioxide to diffuse from the blood into the alveolar air to be expelled. Alveoli provide an immense surface area and very thin barriers, which makes diffusion efficient. The bronchi and trachea are the airways that conduct air but do not participate in gas exchange, while capillaries are the blood vessels involved in transporting gases, with the actual exchange occurring across the alveolar–capillary membrane. So the primary site of respiration in the lungs is the alveoli.