Editing Pneumonia (section)

==Mechanisms==
[[File:New Pneumonia cartoon.jpg|thumb|upright=1.3|alt=A schematic diagram of the human lungs with an empty circle on the left representing a normal alveolus and one on the right showing an alveolus full of fluid as in pneumonia|Pneumonia fills the lung's [[Pulmonary alveolus|alveoli]] with fluid, hindering oxygenation. The alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia.]]

Pneumonia frequently starts as an [[upper respiratory tract infection]] that moves into the lower respiratory tract.<ref name=PedNA09>{{cite journal | vauthors = Ranganathan SC, Sonnappa S | title = Pneumonia and other respiratory infections | journal = Pediatric Clinics of North America | volume = 56 | issue = 1 | pages = 135–56, xi | date = February 2009 | pmid = 19135585 | pmc = 7111724 | doi = 10.1016/j.pcl.2008.10.005 }}</ref> It is a type of pneumonitis (lung inflammation).<ref>{{cite book|last1=Anderson|first1=Douglas M. |title=Dorland's illustrated medical dictionary|date=2000|publisher=Saunders|location=Philadelphia [u.a.]|isbn=978-0-7216-8261-7|page=[https://archive.org/details/trent_0116404640520/page/1414 1414]|edition=29|url=https://archive.org/details/trent_0116404640520/page/1414}}</ref> The normal flora of the upper airway give protection by competing with pathogens for nutrients. In the lower airways, [[Cough reflex|reflexes of the glottis]], actions of [[complement protein]]s and [[immunoglobulin]]s are important for protection. Micro[[Pulmonary aspiration|aspiration]] of contaminated secretions can infect the lower airways and cause pneumonia. The progress of pneumonia is determined by the virulence of the organism; the amount of organism required to start an infection; and the body's immune response against the infection.<ref name="Elena 2015"/>

===Bacterial===
Most bacteria enter the lungs via small aspirations of organisms residing in the throat or nose.<ref name=Clinic2011/> Half of normal people have these small aspirations during sleep.<ref name=M32/> While the throat always contains bacteria, [[virulent|potentially infectious]] ones reside there only at certain times and under certain conditions.<ref name=M32/> A minority of types of bacteria such as ''[[Mycobacterium tuberculosis]]'' and ''Legionella pneumophila'' reach the lungs via contaminated airborne droplets.<ref name=Clinic2011/> Bacteria can also spread via the blood.<ref name=WHOPrevent2012/> Once in the lungs, bacteria may invade the spaces between cells and between alveoli, where the [[macrophage]]s and [[neutrophil]]s (defensive [[white blood cell]]s) attempt to inactivate the bacteria.<ref>{{cite book|editor-last1=Hammer|editor-first1=Gary D.|editor-last2=McPhee|editor-first2=Stephen J. |title=Pathophysiology of disease: an introduction to clinical medicine|year=2010|publisher=McGraw-Hill Medical|location=New York|isbn=978-0-07-162167-0|page=Chapter 4|edition=6th}}</ref> The neutrophils also release cytokines, causing a general activation of the immune system.<ref name=Fein2006>{{cite book|last=Fein|first=Alan |title=Diagnosis and management of pneumonia and other respiratory infections|year=2006|publisher=Professional Communications|location=Caddo, OK|isbn=978-1-884735-63-9|pages=28–29|url=https://books.google.com/books?id=hKdcHK719qgC&pg=PA28|edition=2nd}}</ref> This leads to the fever, chills, and fatigue common in bacterial pneumonia.<ref name=Fein2006/> The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli, resulting in the consolidation seen on chest X-ray.<ref>{{cite book|last=Kumar|first=Vinay|title=Robbins and Cotran pathologic basis of disease.|year=2010|publisher=Saunders/Elsevier|location=Philadelphia|isbn=978-1-4160-3121-5|page=Chapter 15|edition=8th}}</ref>

===Viral===
Viruses may reach the lung by a number of different routes. Respiratory syncytial virus is typically contracted when people touch contaminated objects and then touch their eyes or nose.<ref name=M31>Murray and Nadel (2010). Chapter 31.</ref> Other viral infections occur when contaminated airborne droplets are inhaled through the nose or mouth.<ref name=Clinic2011/> Once in the upper airway, the viruses may make their way into the lungs, where they invade the cells lining the airways, alveoli, or [[lung parenchyma]].<ref name=M31/> Some viruses such as measles and herpes simplex may reach the lungs via the blood.<ref name=Gary2010>{{cite book|editor-last1=Fleisher|editor-first1=Gary R.|editor-last2=Ludwig|editor-first2=Stephen |title=Textbook of pediatric emergency medicine|year=2010|publisher=Wolters Kluwer/Lippincott Williams & Wilkins Health|location=Philadelphia|isbn=978-1-60547-159-4|page=914|url=https://books.google.com/books?id=a7CqcE1ZrFkC&pg=PA914|edition=6th}}</ref> The invasion of the lungs may lead to varying degrees of cell death.<ref name=M31/> When the immune system responds to the infection, even more lung damage may occur.<ref name=M31/> Primarily white blood cells, mainly [[mononuclear cell]]s, generate the inflammation.<ref name=Gary2010/> As well as damaging the lungs, many viruses simultaneously affect other [[organ (anatomy)|organs]] and thus disrupt other body functions. Viruses also make the body more susceptible to bacterial infections; in this way, bacterial pneumonia can occur at the same time as viral pneumonia.<ref name=Viral09>{{cite journal | vauthors = Figueiredo LT | title = Viral pneumonia: epidemiological, clinical, pathophysiological and therapeutic aspects | journal = Jornal Brasileiro de Pneumologia | volume = 35 | issue = 9 | pages = 899–906 | date = September 2009 | pmid = 19820817 | doi = 10.1590/S1806-37132009000900012 | doi-access = free }}</ref>