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

Where does gaseous exchange primarily occur in the lungs?

1. Bronchi

2. Trachea

3. Alveoli

4. Diaphragm

The correct answer is: Alveoli

Gaseous exchange primarily occurs in the alveoli, which are tiny air sacs located at the end of the bronchial tubes within the lungs. These structures are specifically adapted for this function due to their large surface area and thin walls, which facilitate the efficient diffusion of oxygen and carbon dioxide between the air in the alveoli and the blood in the surrounding capillaries. The alveoli are surrounded by numerous capillaries, creating a close relationship between the respiratory and circulatory systems. This arrangement allows oxygen from inhaled air to pass into the bloodstream, where it binds to hemoglobin in red blood cells, while carbon dioxide, a waste product of metabolism, moves from the blood into the alveoli to be exhaled. Other structures mentioned in the question serve different purposes in the respiratory system. The bronchi are responsible for conducting air from the trachea to the lungs but are not the site of gas exchange. The trachea acts as the windpipe that conducts air into the bronchi but also lacks the structural adaptations for gas exchange. The diaphragm is a muscle that plays a crucial role in breathing by contracting and relaxing to allow air to enter and exit the lungs but is not involved in the exchange of gases itself. Thus, the