What happens to particles less than 2 uM in size?

Particles less than 2 micrometers in size typically reach the alveoli of the lungs, where they are encountered by specialized immune cells known as dust cells or alveolar macrophages. These cells play a critical role in the respiratory system's defense mechanism. When these small particles reach the alveoli, the dust cells phagocytize them, effectively engulfing and digesting these potentially harmful particles. This process helps to maintain clean airways and protect the body from inhaled pathogens and pollutants.

The other options do not accurately describe the fate of particles under 2 micrometers in size: sneezing primarily expels larger particles from the upper respiratory tract, while absorption into the bloodstream is generally limited to even smaller particles or soluble substances. Increasing airway resistance is more commonly associated with larger particles or other factors affecting airflow, rather than the behavior of particles that are less than 2 micrometers.