New York State Emergency Medical Technician (EMT) Practice Exam

Where does the actual exchange of oxygen and carbon dioxide occur?

1. Bronchioles

2. Alveolar sacs

3. Apex of the lung

4. Pulmonary capillaries

The correct answer is: Alveolar sacs

The exchange of oxygen and carbon dioxide occurs in the alveolar sacs. These small, balloon-like structures are located at the ends of the bronchioles in the lungs and are crucial for respiration. The walls of the alveoli are extremely thin and surrounded by tiny blood vessels called capillaries. During the breathing process, oxygen from the air in the alveoli diffuses across the alveolar membrane into the blood in the pulmonary capillaries, while carbon dioxide, which is a waste product of metabolism, diffuses in the opposite direction—from the blood into the alveoli to be exhaled. This gas exchange is vital for maintaining the body's oxygen levels and removing carbon dioxide, ensuring proper cellular function and homeostasis. In contrast, while bronchioles are important for conducting air to the alveolar sacs, they do not facilitate the actual gas exchange. The apex of the lung refers to the top part of the lung and does not specifically relate to the gas exchange process, as the majority occurs in the lower regions where more alveoli are present. Pulmonary capillaries play a role in the exchange process, but they do so by connecting to the alveoli rather than being the site of the exchange themselves. Thus, the alveolar sacs