What surrounds the alveoli to facilitate gas exchange?

• A. Bronchioles
• B. Capillaries
• C. Alveolar ducts
• D. Interstitial fluid

Answer: (B)

The alveoli, which are tiny air sacs in the lungs, are surrounded by capillaries to facilitate gas exchange. Capillaries are small blood vessels that allow oxygen and carbon dioxide to diffuse across their walls. When inhaled air reaches the alveoli, the oxygen in the air passes through the thin alveolar walls and into the capillaries. Simultaneously, carbon dioxide, which is a waste product of metabolism in the body, moves from the capillaries into the alveoli to be exhaled.

The close proximity of capillaries to the alveoli ensures that the gases can efficiently exchange due to the large surface area provided by the alveoli and the thin barrier created by both the alveolar and capillary walls. This design is crucial for effective respiration, as it allows the body to take in oxygen and remove carbon dioxide efficiently.

Other choices, while related to the respiratory system, do not play the primary role in the direct exchange of gases. Bronchioles are the small airways that lead to the alveoli, alveolar ducts are passages that connect to the alveoli, and interstitial fluid is a fluid that exists in the space surrounding cells, but it isn't directly facilitating gas exchange. Thus, capill