Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

TracheaThe trachea or windpipe is a tube composed of smooth muscle lined with mucous membrane, andC-shaped rings of cartilage are embedded in the muscle. The trachea extends from below the cricoidcartilage of the larynx to the carina, and is about 2.5 cm in diameter and about 10 cm long. Thetrachea forms a major part of the passageway through which external air reaches the lungs, the simplebut vital function of this structure. The trachea is a rare tumor site.BronchiAt its lower end, the trachea divides into the right main stem bronchus and left main stembronchus (primary bronchi) at the carina. The walls of the bronchi are made of cartilage with aciliated mucous lining. The extrapulmonary portion of each bronchus enters the lung on its own sideand immediately divides into branches called lobar (secondary) bronchi. The secondary bronchicontinue to branch, forming bronchioles which become smaller and smaller, forming microscopicbranches which divide into alveolar ducts. At the terminal ducts are grape-like formations known asalveolar sacs which provide surfaces where the exchange of air and carbon dioxide takes place.The intrapulmonary (lobar) bronchi are lined with ciliated columnar, mucin-producing epithelium.The walls are composed of a submucosa, smooth muscle, fibrous tissue and cartilage.149