How do capillaries facilitate gas exchange?

Capillaries facilitate gas exchange primarily through their intimate association with alveoli in the lungs. Each alveolus, which is the functional unit of the lung where gas exchange takes place, is surrounded by a dense network of capillaries. This close proximity allows for the efficient transfer of gases, specifically oxygen and carbon dioxide.

When we inhale, oxygen enters the alveoli, where it diffuses through the thin walls of both the alveoli and the surrounding capillaries into the bloodstream. Conversely, carbon dioxide, which is a waste product of metabolism, moves from the blood in the capillaries into the alveoli to be exhaled. This process is driven by concentration gradients, ensuring that oxygen is absorbed into the bloodstream while carbon dioxide is expelled from it.

The other choices do not accurately describe the function of capillaries in gas exchange. While expanding blood flow can assist in delivering oxygen-rich blood to tissues, it is not the primary mechanism of gas exchange. Filtering air is a function of the upper respiratory system, not capillaries. Lastly, while waste can be transported to the lungs for exhalation, capillaries specifically facilitate the exchange of gases at the alveoli rather than carrying waste from the body. Understanding this context helps