Editing Trachea (section)

===Development===
In the fourth week of [[human embryogenesis|development of the human embryo]] as the [[respiratory bud]] grows, the trachea separates from the [[foregut]] through the formation of ridges which eventually separate the trachea from the oesophagus, the [[tracheoesophageal septum]]. This separates the future trachea from the oesophagus and divides the foregut tube into the laryngotracheal tube.<ref name=Langmans2019 >{{cite book | vauthors = Sadley TW |title=Langman's medical embryology |date=2019|location=Philadelphia|publisher=Wolters Kluwer |isbn=9781496383907 |edition=14th|pages=223–229}}</ref> By the start of the fifth week, the left and right main bronchi have begun to form, initially as buds at the terminal end of the trachea.<ref name=Langmans2019 />

The trachea is no more than 4&nbsp;mm in diameter during the first year of life, expanding to its adult diameter of approximately 2&nbsp;cm by late childhood.<ref name=GA2016 /><ref name="Furlow2018" /> The trachea is more circular and more vertical in children compared to adults,<ref name="Furlow2018" /> varies more in size, and also varies more in its position in relation to its surrounding structures.<ref name="GA2016" />