Editing Lung (section)

===Obstructive lung diseases===
[[File: Respiratory tract.jpg|thumb|3D still image of constricted airways as in bronchial asthma]]
[[File:Emphysema H and E.jpg|thumb|Lung tissue affected by emphysema using [[H&E stain]]]]
<!-- Obstructive lung disease-->[[Asthma]], [[bronchiectasis]], and [[chronic obstructive pulmonary disease]] (COPD) that includes [[Bronchitis#Chronic bronchitis|chronic bronchitis]], and [[emphysema]], are all [[obstructive lung disease]]s characterised by [[airway obstruction]]. This limits the amount of air that is able to enter alveoli because of constriction of the bronchial tree, due to inflammation. Obstructive lung diseases are often identified because of symptoms and diagnosed with [[pulmonary function tests]] such as [[spirometry]]. 

Many obstructive lung diseases are managed by avoiding triggers (such as [[dust mite]]s or [[smoking]]), with symptom control such as [[bronchodilator]]s, and with suppression of inflammation (such as through [[corticosteroid]]s) in severe cases. A common cause of chronic bronchitis, and emphysema, is smoking; and common causes of [[bronchiectasis]] include severe infections and [[cystic fibrosis]]. The definitive cause of [[asthma]] is not yet known, but it has been linked to other atopic diseases.<ref name=DAVIDSONS2014 /><ref>{{Cite journal |last1=Galli |first1=Elena |last2=Gianni |first2=Simona |last3=Auricchio |first3=Giovanni |last4=Brunetti |first4=Ercole |last5=Mancino |first5=Giorgio |last6=Rossi |first6=Paolo |date=2007-09-01 |title=Atopic dermatitis and asthma |url=http://www.ingentaconnect.com/content/10.2500/aap2007.28.3048 |journal=Allergy and Asthma Proceedings |language=en |volume=28 |issue=5 |pages=540–543 |doi=10.2500/aap2007.28.3048 |pmid=18034972 |issn=1088-5412}}</ref>

The breakdown of alveolar tissue, often as a result of tobacco-smoking leads to emphysema, which can become severe enough to develop into COPD. [[Elastase]] breaks down the [[elastin]] in the lung's connective tissue that can also result in emphysema. Elastase is inhibited by the [[acute-phase protein]], [[alpha-1 antitrypsin]], and when there is a [[Alpha-1 antitrypsin deficiency|deficiency]] in this, emphysema can develop. With persistent stress from smoking, the [[airway basal cell]]s become disarranged and lose their regenerative ability needed to repair the epithelial barrier. The disorganised basal cells are seen to be responsible for the major airway changes that are characteristic of [[COPD]], and with continued stress can undergo a malignant transformation. Studies have shown that the initial development of emphysema is centred on the early changes in the airway epithelium of the small airways.<ref name="Crystal" /> Basal cells become further deranged in a smoker's transition to clinically defined COPD.<ref name="Crystal">{{cite journal |last1=Crystal |first1=RG |title=Airway basal cells. The "smoking gun" of chronic obstructive pulmonary disease. |journal=American Journal of Respiratory and Critical Care Medicine |date=15 December 2014 |volume=190 |issue=12 |pages=1355–62 |doi=10.1164/rccm.201408-1492PP |pmid=25354273|pmc=4299651 }}</ref>