A 6-year-old boy playing in a dusty field in windy weather inhales many small particles that become lodged in his terminal bronchioles. Which of the following respiratory components is most important in clearing these particles?

Question

A 6-year-old boy playing in a dusty field in windy weather inhales many small particles that become lodged in his terminal bronchioles.  Which of the following respiratory components is most important in clearing these particles?

Quizplus · Accepted Answer

11ec160b_3ce6_e963_9249_d76aa061dbfc_MD0001_00 Mucociliary clearance is responsible for removing the vast majority of inhaled particles that lodge within the bronchial tree. Ciliated mucosal epithelium lines the pulmonary airways from the trachea to the proximal portions of the respiratory bronchioles. Mucus and fluid secreted onto this epithelial surface act to trap particles suspended in the inspired air. The trapped particles are constantly swept upward from the bronchioles toward the pharynx by cilia that collectively beat in the direction of the pharynx. The mucus and debris are then swallowed or expectorated upon reaching the pharynx. The terminal bronchioles are covered by ciliated cuboidal epithelium and club cells, which help with mucociliary clearance in this region. (Choice B) Goblet cells are mucus-secreting cells that are interspersed throughout the respiratory mucosa from the trachea down to the larger bronchioles. However, they are not found within the terminal bronchioles. This region is lined by a surfactant-containing fluid secreted by club cells that is continuous with the more proximal mucous layer. (Choice C) Clearance of particles that lodge distal to the terminal bronchioles is dependent on phagocytosis by alveolar macrophages. These cells can destroy some inhaled particles (eg, bacteria) by lysosomal degradation. Nondigestible material must be transported by macrophages to the pulmonary lymphatics or to the terminal bronchioles (for clearance by the mucociliary system). (Choice D) Submucosal mucous and mucoserous glands help form the mucous layer in the larger airways. They are found within the trachea and bronchi but not in the bronchioles. (Choices E and F) Type I and type II pneumocytes line the alveolar ducts and alveoli. Type I pneumocytes are thin cells stretched across the alveolar wall that mediate gas exchange. Type II pneumocytes produce surfactant and divide and differentiate into type I pneumocytes to replace damaged cells. Educational objective: Most inhaled particles that lodge in the bronchial tree are removed via proximal transport by ciliated epithelial cells (mucociliary clearance). Mucus-secreting cells are present to the level of the larger bronchioles, after which club cells become the prominent secretory cell type.

A 6-Year-Old Boy Playing in a Dusty Field in Windy