New York State Basic Emergency Medical Technician (EMT-B) Practice Exam

Which structure is responsible for the exchange of oxygen and carbon dioxide in the lungs?

1. Bronchioles

2. Alveoli

3. Pleura

4. Capillaries

The correct answer is: Alveoli

The alveoli are the tiny air sacs in the lungs where the critical exchange of oxygen and carbon dioxide occurs. They are surrounded by a network of capillaries, which facilitate the transfer of these gases between the air and the bloodstream. When oxygen-rich air is inhaled, it enters the alveoli, where oxygen passes through the alveolar walls into the capillaries and into the bloodstream. At the same time, carbon dioxide from the blood moves from the capillaries into the alveoli to be exhaled. This process allows for the replenishment of oxygen in the blood while removing carbon dioxide, which is a waste product of metabolism. Other structures mentioned play supportive roles but do not directly engage in gas exchange. The bronchioles are the small passageways through which air travels to reach the alveoli but are not the sites of gas exchange. The pleura are membranes that surround the lungs and help with the lung expansion and contraction during breathing but are also not involved in gas exchange. Capillaries, while essential for transporting gases, are the vessels that surround the alveoli and are part of the exchange mechanism rather than the primary site of exchange itself.