Editing Lung (section)

====Respiratory zone====
The conducting zone of the respiratory tract ends at the terminal bronchioles when they branch into the respiratory bronchioles. This marks the beginning of the terminal respiratory unit called the '''acinus''' which includes the respiratory bronchioles, the alveolar ducts, [[alveolar sac]]s, and alveoli.<ref name ="Weinberger2">{{Cite book|title=Principles of Pulmonary Medicine|last=Weinberger|first=Steven|publisher=Elsevier|year=2019|isbn=9780323523714|page=2}}</ref> An acinus measures up to 10&nbsp;mm in diameter.<ref name=Hochhegger/> A '''primary pulmonary lobule''' is the part of the lung distal to the respiratory bronchiole.<ref name="Elsevier-2021">{{Cite book |title=Gray's Anatomy: the anatomical basis of clinical practice |date=2021 |publisher=Elsevier |isbn=978-0-7020-7705-0 |editor-last=Gray |editor-first=Henry |edition=42nd |location=Amsterdam |pages=1028 |editor-last2=Standring |editor-first2=Susan |editor-last3=Anhand |editor-first3=Neel}}</ref> Thus, it includes the alveolar ducts, sacs, and alveoli but not the respiratory bronchioles.<ref name=Goel>{{Cite web|url=https://radiopaedia.org/articles/primary-pulmonary-lobule?lang=gb|title=Primary pulmonary lobule|last=Goel|first=A|access-date=12 July 2019}}</ref> 

The unit described as the '''secondary pulmonary lobule''' is the lobule most referred to as the '''pulmonary lobule''' or '''respiratory lobule'''.<ref name="GuytonHall"/>{{rp|489}}<ref name=Gaillard>{{Cite web|url=https://radiopaedia.org/articles/secondary-pulmonary-lobule?lang=gb|title=Secondary pulmonary lobule|last1=Gilcrease-Garcia|first1=B|last2=Gaillard|first2=Frank|website=radiopaedia.org|access-date=10 August 2019}}</ref> This lobule is a discrete unit that is the smallest component of the lung that can be seen without aid.<ref name="Elsevier-2021" /> The secondary pulmonary lobule is likely to be made up of between 30 and 50 primary lobules.<ref name=Goel/> The lobule is supplied by a terminal bronchiole that branches into respiratory bronchioles. The respiratory bronchioles supply the alveoli in each acinus and is accompanied by a [[pulmonary artery]] branch. Each lobule is enclosed by an interlobular septum. Each acinus is incompletely separated by an intralobular septum.<ref name=Hochhegger>{{Cite journal|last=Hochhegger|first=B|date=June 2019|title=Pulmonary Acinus: Understanding the Computed Tomography Findings from an Acinar Perspective.|journal=Lung|volume=197|issue=3|pages=259–265|pmid=30900014|doi=10.1007/s00408-019-00214-7|s2cid=84846517|hdl=10923/17852|hdl-access=free}}</ref>

The respiratory bronchiole gives rise to the alveolar ducts that lead to the alveolar sacs, which contain two or more alveoli.<ref name=Pocock/> The walls of the alveoli are extremely thin allowing a fast rate of [[Diffusion#Diffusion vs. bulk flow|diffusion]].  The alveoli have interconnecting small air passages in their walls known as the [[pores of Kohn]].<ref name=Pocock/>