Trachea and Bronchi
■ Begins at the inferior border of the cricoid cartilage (C6) as a continuation of the larynx and ends by bifurcating into the right and left main stem bronchi at the level of the sternal angle (disc between T4 and T5).
■ Is approximately 12 cm in length and has 16 to 20 incomplete hyaline cartilaginous rings that open posteriorly toward the esophagus and prevent the trachea from collapsing.
■ May be compressed by an aortic arch aneurysm, a goiter, or thyroid tumors, causing dyspnea.
■ Has the carina, a downward and backward projection of the last tracheal cartilage, which lies at the level of the sternal angle and forms a keel-like ridge separating the openings of the right and left main bronchi.
■ Carina may be distorted, widened posteriorly, and immobile in the presence of a bronchogenic carcinoma. The mucous membrane over the carina is one of the most sensitive areas of the tracheobronchial tree and is associated with the cough reflex.
Right Main (Primary) Bronchus
■ Is shorter, wider, and more vertical than the left main bronchus; therefore, more foreign bodies that enter through the trachea are lodged in this bronchus or inferior lobar bronchus.
■ Runs under the arch of the azygos vein and divides into three lobar or secondary (superior, middle, and inferior) bronchi and fi nally into 10 segmental bronchi. The right superior lobar (secondary) bronchus is known as the eparterial (above the artery) bronchus because it passes above the level of the pulmonary artery. All others are the hyparterial bronchi.
Left Main (Primary) Bronchus
■ Runs inferolaterally inferior to the arch of the aorta, crosses anterior to the esophagus and thoracic aorta, and divides into two lobar or secondary bronchi, the upper and lower, and finally into 8 to 10 segmental bronchi.
■ Is also crossed superiorly by the arch of the aorta over its proximal part and by the left pulmonary artery over its distal part.
■ Dilates its lumen by sympathetic nerves and constricts by parasympathetic stimulation.