Which MMAD value corresponds to the parenchyma of the lungs?

To determine which MMAD (Mass Median Aerodynamic Diameter) value corresponds to the parenchyma of the lungs, it is important to understand the sizes of particles that can reach different areas of the respiratory system. The parenchyma refers to the functional tissue of the lungs, primarily the alveoli, where gas exchange occurs.

Particles that have an aerodynamic diameter of less than 0.1 nanometers are sufficiently small to penetrate deep into the lungs, reaching the alveolar regions for efficient gas exchange. These ultra-fine particles can travel beyond the upper airways and bronchi, making them capable of deposition in the lower respiratory tract, which includes the alveoli that constitute the parenchyma.

Larger particles, such as those in the ranges provided in the other choices, are more likely to be trapped in the upper airways or the bronchial tubes rather than reaching the alveolar region. Thus, the correct MMAD value that represents particles able to deposit in the parenchyma of the lungs is indeed less than 0.1 nm.