Pathophysiology


Influenza is an acute viral infection of the upper respiratory tract and sometimes the lungs. Following transmission, the virus attaches to, and penetrates, the ciliated epithelial cells in the nasopharynx, trachea and bronchi. Viral replication results in the destruction of these epithelial cells. Epithelial necrosis initiates the inflammatory response that results in the flu symptoms of: fever, chills, muscle ache, headache, prostration and anorexia.

In the event that the virus infects the lungs, loss of alveolar epithelium allows plasma to leak from capillaries into the alveolar space. This is especially problematic in patients predisposed to pulmonary edema. Pulmonary edema can be caused by any of the following underlying conditions: (1) increased capillary hydrostatic pressure, (2) increased capillary permeability, (3) decreased plasma oncotic pressure, and (4) lymphatic obstruction.

Loss of alveolar epithelium and the resulting pulmonary edema predispose the underlying tissue to colonization by bacteria. Secondary bacterial infection can lead to pneumonia, which accounts for most influenza related deaths.


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Flu symptoms result from:
Cell damage induced inflammatory response
Viral replication



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