Community-acquired pneumonia pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Chetan Lokhande, M.B.B.S [2]
Pathophysiology
Modes of transmission
Microaspiration of oropharyngeal contents
Inoculation of lung by pathogenetic organisms is one of the mechanism of acquiring pneumonia. It most commonly occurs in normal persons during sleep , in unconscious persons due to impaired gag reflex, cough reflex or gastroesopahegeal reflux.
Inhalation of aerosolized droplets
Inhalation of aerosolized droplets of 0.5 to 1 micrometer is the most common pathway of acquiring pneumonia. A few bacterial and viral infections are transmitted in this fashion. The lung can normally filter out particles between 0.5 to 2 micrometer by recruiting the alveolar macrophages.[1]
Blood borne or sytemic infection
Another way of acquiring poneumonia systematically is through blood. Blood-borne pneumonia is more common in intravenous drug users . Staphylococcal aureus causes pneumonia in this way. Gram negative bacteria can be found to cause pneumonia in immunocompromised individuals.
Trauma or Local spread
Pneumonia can be caused iatrogenically by a surgeon during an operative procedure or by a penetrating trauma to the lung . A local spread of a hepatic abscess and amoebic abscess can also cause pneumonia.
Pathogenetic mechanism
The lung can normally filter out large droplets of aerosols. Smaller droplets of the size of 0.5 to 2 micrometer are deposited on the alveoli and then engulfed by alevolar macrophages. These macrophages release cytokines and chemokines , which also includes tumor necrosis factor- alpha , interleukin-8 and leukotriene B4 . The neutrophils are recruited by these cells and they kill these micro-organisms.[2][3]
References
- ↑ Wunderink, RG.; Waterer, GW. (2004). "Community-acquired pneumonia: pathophysiology and host factors with focus on possible new approaches to management of lower respiratory tract infections". Infect Dis Clin North Am. 18 (4): 743–59, vii. doi:10.1016/j.idc.2004.07.004. PMID 15555822. Unknown parameter
|month=ignored (help) - ↑ Strieter, RM.; Belperio, JA.; Keane, MP. (2003). "Host innate defenses in the lung: the role of cytokines". Curr Opin Infect Dis. 16 (3): 193–8. doi:10.1097/01.qco.0000073766.11390.0e. PMID 12821807. Unknown parameter
|month=ignored (help) - ↑ Mason, CM.; Nelson, S. (2005). "Pulmonary host defenses and factors predisposing to lung infection". Clin Chest Med. 26 (1): 11–7. doi:10.1016/j.ccm.2004.10.018. PMID 15802161. Unknown parameter
|month=ignored (help)