A 67-year-old male presents to the emergency department with a productive cough and dyspnea that started 1 week ago. He has a past medical history of hypertension that is appropriately managed with chlorthalidone. Social history and family history are unremarkable. Vital signs are temperature 38.9° C (102° F), blood pressure 128/82 mmHg, pulse 93 beats/minute, and respirations 22/minute. The patient is 71 inches and weighs 198 pounds. Physical examination reveals mild tachypnea and rhonchi at the left lung base. Chest x-ray reveals a left lower lobe consolidation.
Based on the patient’s clinical picture, which of the following cells is most likely to be damaged?
D: Type 1 pneumocytes
Type 1 pneumocytes are thin squamous cells that are chiefly responsible for gas exchange. They comprise 95% of the alveolar area. In the presence of pneumonia (fever, productive cough, dyspnea, and consolidation on imaging) resulting injury leads to damage of this thin squamous cell. Damage to the cell responsible for gas exchange impairs normal physiological respiratory function. This results in a decreased ventilation/perfusion (VQ) ratio and a compensatory increase in respiratory rate, as seen in this patient, to offset this loss of function.
Answer Choice A: Club cells, is incorrect. Club cells are responsible for maintaining epithelium in the respiratory bronchioles. These cells are not especially susceptible to injury.
Answer Choice B: Dust cells, is incorrect. Dust cells are macrophages within alveoli and alveolar ducts. They are responsible for clearing foreign debris from the alveolar space and are not the cell type that is most likely to be damaged in the presence of infection.
Answer Choice C: Goblet cells, is incorrect. Goblet cells are found in the trachea and bronchi. They are mucous-producing cells. These cells are not susceptible to damage in the presence of pneumonia.
Answer Choice E: Type 2 pneumocytes, is incorrect. Type 2 pneumocytes are responsible for surfactant production in the alveoli. Following injury to the alveoli, type 2 pneumocytes are responsible for regeneration of type 1 pneumocytes.
Key Learning Point
A pathological process that causes alveolar lung injury is most likely to result in type 1 pneumocyte injury. Type 1 pneumocytes are responsible for gas exchange and are most commonly damaged as a result of lung injuries. Type 2 pneumocytes can trigger the regeneration and proliferation of type 1 pneumocytes following injury.
