## Route of Silica Exposure in Occupational Silicosis **Key Point:** Silica dust enters the body primarily through inhalation, where fine particles (<5 μm) penetrate deep into the alveoli and cause chronic inflammation and fibrosis. ### Pathophysiology of Silica Inhalation 1. **Particle size matters**: Respirable silica particles (0.5–5 μm) bypass upper airway defenses and deposit in the alveolar region 2. **Macrophage activation**: Silica crystals are phagocytosed by alveolar macrophages, triggering inflammatory cytokine release (TNF-α, IL-1, IL-6) 3. **Progressive fibrosis**: Chronic silica exposure leads to nodular fibrosis, particularly in the upper lung zones ### Why Other Routes Are Negligible | Route | Why Not Primary | |-------|------------------| | Ingestion | Silica is poorly absorbed from GI tract; swallowed particles are excreted unchanged | | Dermal | Silica cannot penetrate intact skin; no systemic toxicity from skin contact | | Parenteral | Occupational silicosis is not caused by traumatic inoculation | **High-Yield:** Silicosis is a **pneumoconiosis** — a lung disease caused exclusively by inhalation of mineral dust. It is one of the most common occupational lung diseases globally, particularly in mining, sandblasting, foundry work, and stone-cutting industries. **Clinical Pearl:** The latency period for silicosis is typically 10–20 years; workers exposed to high concentrations may develop acute silicosis in 5–10 years.
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