Which of the following is included by major defense mechanisms of the respiratory system?
A. Phagocytic activity of type II pneumocytes B. Specific cell killing by type I pneumocytes C. Mucociliary action for tracheobronchial clearance D. The pores of Kohn E. Phagocytic activity by Clara cells
Mucociliary action for tracheobronchial clearance -mucociliary action is critical in protecting the respiratory system, which is exposed to constant assault from the environment. to protect the distal portions of the lung, which under normal conditions are considered a sterile environment, extensive defense mechanisms have evolved. nasal clearance of material occurs through sneezing, whereas other material located posteriorly may be swept into the nasopharynx. the mucociliary action within the trachea and bronchi is often called the mucociliary, or tracheobronchial, escalator. at the distal end of the system, the alveolar macrophages phagocytose foreign material and secrete and respond to an array of cytokines. the type ii pneumocytes resorb as well as secrete surfactant and surfactant associated proteins that have some antiviral and antibacterial function. in the bronchi, there is extensive associated lymphoid tissue (balt), which is analogous to the mucosa-associated lymphoid tissue (malt) of the gut and the skin-associated lymphoid tissue (salt). there are b and t cell areas throughout the balt. the b cells are precursors of plasma cells and synthesize immunoglobulins such as iga associated with the bronchial secretion. helper t cells recognize foreign antigen in association with class ii major histocompatibility complex (mhc) molecules. cytotoxic t cells recognize fragments of antigen (specifically viral fragments) on the surface of viral-infected cells in association with class i mhc. antigen-presenting cells (i.e., alveolar macrophages) also function in a similar fashion to those found elsewhere in the body; they present antigen to helper t cells in conjunction with class ii mhc.