Which of the following pathophysiological mechanisms that occur in the lung parenchyma allows pneumonia to develop?
A. Atelectasis
B. Bronchiectasis
C. Effusion
D. Inflammation
Correct Answer: D. Inflammation
The most common feature of all types of pneumonia is an inflammatory pulmonary response to the offending organism or agent. The resident macrophages serve to protect the lung from foreign pathogens. Ironically, the inflammatory reaction triggered by these very macrophages is what is responsible for the histopathological and clinical findings seen in pneumonia.
Option A: Atelectasis indicates a collapse of a portion of the airway that doesn’t occur with pneumonia. It is caused by the partial or complete, reversible collapse of the small airways resulting in an impaired exchange of CO2 and O2 – i.e., intrapulmonary shunt. The incidence of atelectasis in patients undergoing general anesthesia is 90%.
Option B: Bronchiectasis is a chronic lung disease characterized by persistent and lifelong widening of the bronchial airways and weakening of the function mucociliary transport mechanism owing to repeated infection contributing to bacterial invasion and mucus pooling throughout the bronchial tree.
Option C: An effusion is an accumulation of excess pleural fluid in the pleural space, which may be a secondary response to pneumonia. Accumulation of excess fluid can occur if there is excessive production or decreased absorption or both overwhelming the normal homeostatic mechanism. If pleural effusion is mainly due to mechanisms that lead to pleural effusion mainly due to increased hydrostatic pressure are usually transudative, and leading to pleural effusion have altered the balance between hydrostatic and oncotic pressures (usually transudates), increased mesothelial and capillary permeability (usually exudates) or impaired lymphatic drainage.
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