A 45-year-old man is evaluated for persistent cough and progressive dyspnea on exertion. The patient has no medical issues but has been exposed to large quantities of coal dust while working as a miner for the past 15 years. Chest imaging reveals small, nodular opacities in the upper lobes. Lung biopsy shows fine carbon particles within the patient's respiratory bronchioles and alveolar ducts. Which of the following mechanisms is most directly responsible for clearing the foreign particles from this patient's respiratory tract?

Question

A 45-year-old man is evaluated for persistent cough and progressive dyspnea on exertion.  The patient has no medical issues but has been exposed to large quantities of coal dust while working as a miner for the past 15 years.  Chest imaging reveals small, nodular opacities in the upper lobes.  Lung biopsy shows fine carbon particles within the patient's respiratory bronchioles and alveolar ducts.  Which of the following mechanisms is most directly responsible for clearing the foreign particles from this patient's respiratory tract?

Quizplus · Accepted Answer

11ec160b_3ce6_9b42_9249_339c43aa8509_MD0001_00 This patient has coal worker pneumoconiosis, a form of interstitial lung fibrosis secondary to long-term inhalation of coal particles. Inorganic dust is constantly being inhaled and must be cleared by the respiratory tract to prevent disease. The clearance mechanisms used by the lungs vary depending on the size of the particles. Larger particles become trapped by mucus secretions in the trachea, bronchi, and proximal bronchioles; these trapped particles are swept upward toward the pharynx by the collective beating of ciliated cells. The finest particles (<2 µm) can travel past the highly ciliated airways into the respiratory bronchioles and alveoli, where they are phagocytized by alveolar macrophages. Engulfment of inorganic dust causes macrophage activation and the release of a number of cytokines that induce pulmonary inflammation. Growth factors, including platelet-derived growth factor and insulin-like growth factor, are also released and stimulate fibroblasts to proliferate and produce collagen. This production results in progressive interstitial lung fibrosis that characterizes the pneumoconioses. (Choices A and E) The largest dust particles become trapped in the upper airways (eg, nasal passages, pharynx) and are cleared through coughing and sneezing. (Choice B) Immunologic memory can help with the clearance of previously encountered microorganisms but would not contribute to the removal of inorganic dust particles. (Choice C) Mucociliary transport is the primary means of eliminating particles that lodge in the bronchi and bronchioles (typically, medium-sized particles). Educational objective: The pneumoconioses are diseases resulting from the inhalation of fine dust particles that reach the respiratory bronchioles and alveoli. Particles that lodge in this region are normally cleared by alveolar macrophages. High particulate burden can cause the excessive release of cytokines from macrophages, resulting in progressive pulmonary fibrosis.

A 45-Year-Old Man Is Evaluated for Persistent Cough and Progressive