The alveolar structure primarily responsible for gas exchange is the

The alveolar structure primarily responsible for gas exchange is the

• A. Trachea
• B. Alveolus
• C. Bronchus
• D. Bronchioles

Answer: (B)

Gas exchange happens where air meets blood across an extremely thin, expansive surface. That place is the alveolus, the tiny sac at the end of the respiratory tree. Its walls are essentially one cell thick and are surrounded by a dense capillary network, providing a large surface area for diffusion. Oxygen moves from the alveolar air into the blood, while carbon dioxide moves from the blood into the alveolar air to be exhaled. Type I cells form the thin barrier for diffusion, and type II cells secrete surfactant to keep the surface stable and prevent collapse, supporting efficient gas transfer. The trachea, bronchi, and bronchioles are conducting airways; they transport air but do not have the thin barrier and extensive capillary network needed for gas exchange.

Gas exchange happens where air meets blood across an extremely thin, expansive surface. That place is the alveolus, the tiny sac at the end of the respiratory tree. Its walls are essentially one cell thick and are surrounded by a dense capillary network, providing a large surface area for diffusion. Oxygen moves from the alveolar air into the blood, while carbon dioxide moves from the blood into the alveolar air to be exhaled. Type I cells form the thin barrier for diffusion, and type II cells secrete surfactant to keep the surface stable and prevent collapse, supporting efficient gas transfer. The trachea, bronchi, and bronchioles are conducting airways; they transport air but do not have the thin barrier and extensive capillary network needed for gas exchange.