A nurse is explaining to a patient with chronic obstructive pulmonary disease (COPD) how gas exchange occurs in the lungs. Which of the following best describes the role and location of the alveoli in this process?

A. Alveoli are located in the nasal cavity and help warm and humidify the air before it reaches the lungs is incorrect because the nasal cavity and upper airways warm, humidify, and filter inhaled air, but alveoli are located deep within the lungs, not in the nasal cavity. B. Alveoli are tiny air sacs located at the end of the bronchial tubes where oxygen and carbon dioxide are exchanged is correct because alveoli are microscopic sac-like structures clustered at the ends of bronchioles. They are the primary site of gas exchange in the lungs, where oxygen diffuses into the blood and carbon dioxide diffuses out of the blood across the alveolar-capillary membrane. This process is essential for oxygenating the body and removing metabolic waste. C. Alveoli are muscular structures in the lungs that contract to help expel air during exhalation is incorrect because alveoli do not have muscles for contraction. Air movement is facilitated by the diaphragm and intercostal muscles, not the alveoli themselves. D. Alveoli are large cavities in the lungs that filter out dust particles and other pollutants is incorrect because filtration of dust and particles primarily occurs in the upper respiratory tract (nose, trachea, bronchi) via mucus and cilia, not in alveoli. Alveoli are tiny sacs specialized for efficient gas diffusion, not filtering.