Trachea

Trachea (WIND-PIPE). The trachea extends from the lower part of the larynx to about the level of the third dorsal vertebra, where it divides into the two bronchi. The framework of the trachea consists of a series of cartilaginous rings, from 16 to 20 in number, which do not extend completely round the tube, but are deficient behind, where the cartilage is replaced by fibrous tissue. Within the rings is disposed the mucous tissue of the trachea internal to which is the stratified columnar epithelium, which forms the inner lining of the tube; the most superficial cells, those which abut upon the lumen of the trachea, are ciliated. At the division of the trachea into the two bronchi, the latter are not quite symmetrically disposed with regard to the former, and when a foreign body obtains access to the trachea it is usually found that it penetrates into the right rather than into the left bronchus. The trachea is sometimes affected by inflammation, usually as the result of the extension of mischief from the larynx.