Which particle size category would most likely reach the alveolar region?

Which particle size category would most likely reach the alveolar region?

• A. Large particles
• B. Medium particles
• C. Small particles
• D. Any particle can reach alveoli

Answer: (C)

The key idea is how particle size determines where inhaled particles deposit in the lungs. Large particles have enough inertia to crash into the nose and upper airways, so they don’t reach the alveoli. Medium-sized particles tend to deposit earlier, in the bronchiolar regions. Small particles, in the respirable size range (roughly 1–3 μm, up to about 5 μm), can bypass upper-airway impaction and settle or diffuse deep into the lungs, reaching the alveolar region. That’s why small particles are the most likely to reach the alveoli.

The key idea is how particle size determines where inhaled particles deposit in the lungs. Large particles have enough inertia to crash into the nose and upper airways, so they don’t reach the alveoli. Medium-sized particles tend to deposit earlier, in the bronchiolar regions. Small particles, in the respirable size range (roughly 1–3 μm, up to about 5 μm), can bypass upper-airway impaction and settle or diffuse deep into the lungs, reaching the alveolar region. That’s why small particles are the most likely to reach the alveoli.