Which small air sacs are the site of gas exchange in the lungs?

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Multiple Choice

Which small air sacs are the site of gas exchange in the lungs?

Gas exchange in the lungs occurs across the walls of the tiny air sacs called alveoli. These alveoli form an enormous surface area and have extremely thin walls with a dense network of capillaries just outside them. This close association lets oxygen from the air in the alveoli diffuse into the blood, and carbon dioxide from the blood diffuse into the alveolar air to be exhaled. The lining and structure of the alveoli, including thin septa and a small distance between air and blood (the respiratory membrane), optimize diffusion. Other airway structures don’t specialize in gas exchange. The bronchioles primarily conduct air and have relatively little surface area for diffusion. The trachea is a larger rigid airway, not a gas-exchange surface. The pleura is a membrane surrounding the lungs, not involved in gas transfer.

Gas exchange in the lungs occurs across the walls of the tiny air sacs called alveoli. These alveoli form an enormous surface area and have extremely thin walls with a dense network of capillaries just outside them. This close association lets oxygen from the air in the alveoli diffuse into the blood, and carbon dioxide from the blood diffuse into the alveolar air to be exhaled. The lining and structure of the alveoli, including thin septa and a small distance between air and blood (the respiratory membrane), optimize diffusion.

Other airway structures don’t specialize in gas exchange. The bronchioles primarily conduct air and have relatively little surface area for diffusion. The trachea is a larger rigid airway, not a gas-exchange surface. The pleura is a membrane surrounding the lungs, not involved in gas transfer.

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