Editing Lung (section)

====Respiratory epithelium====
{{Main|Respiratory epithelium}}
All of the lower respiratory tract including the trachea, bronchi, and bronchioles is lined with [[respiratory epithelium]]. This is a [[cilium|ciliated]] epithelium interspersed with [[goblet cell]]s which produce [[mucin]] the main component of [[mucus]], ciliated cells, [[airway basal cell|basal cells]], and in the [[terminal bronchiole]]s–[[club cells]] with actions similar to basal cells, and [[macrophage]]s. The epithelial cells, and the [[submucosal gland]]s throughout the respiratory tract secrete [[Mucus#Respiratory system|airway surface liquid]] (ASL), the composition of which is tightly regulated and determines how well [[mucociliary clearance]] works.<ref>{{cite journal | last1 = Stanke | first1 = F | year = 2015 | title = The Contribution of the Airway Epithelial Cell to Host Defense | journal = Mediators Inflamm | volume = 2015 | page = 463016 | doi = 10.1155/2015/463016 | pmid=26185361 | pmc=4491388| doi-access = free }}</ref>

[[Neuroendocrine cell#Pulmonary neuroendocrine cells|Pulmonary neuroendocrine cells]] are found throughout the respiratory epithelium including the alveolar epithelium,<ref name="Van Lommel">{{cite journal |last1=Van Lommel |first1=A |title=Pulmonary neuroendocrine cells (PNEC) and neuroepithelial bodies (NEB): chemoreceptors and regulators of lung development. |journal=Paediatric Respiratory Reviews |date=June 2001 |volume=2 |issue=2 |pages=171–6 |pmid=12531066|doi=10.1053/prrv.2000.0126 }}</ref> though they only account for around 0.5 percent of the total epithelial population.<ref name="Garg">{{cite book |doi=10.1016/bs.ctdb.2018.12.002 |chapter=Consider the lung as a sensory organ: A tip from pulmonary neuroendocrine cells |title=Organ Development |series=Current Topics in Developmental Biology |year=2019 |last1=Garg |first1=Ankur |last2=Sui |first2=Pengfei |last3=Verheyden |first3=Jamie M. |last4=Young |first4=Lisa R. |last5=Sun |first5=Xin |volume=132 |pages=67–89 |pmid=30797518 |isbn=9780128104897 |s2cid=73489416 }}</ref> PNECs are innervated airway epithelial cells that are particularly focused at airway junction points.<ref name="Garg"/> These cells can produce serotonin, dopamine, and norepinephrine, as well as polypeptide products. Cytoplasmic processes from the pulmonary neuroendocrine cells extend into the airway lumen where they may sense the composition of inspired gas.<ref name="Weinberger">{{cite book |last1=Weinberger |first1=S |last2=Cockrill |first2=B |last3=Mandel |first3=J |title=Principles of pulmonary medicine |date=2019 |isbn=9780323523714 |page=67 |publisher=Elsevier |edition=Seventh}}</ref>