Question

What is the level of bifurcation of the trachea in a living person?

Answer 1

Hint: Foreign bodies that reside in the trachea are more likely to enter the proper bronchus. The mucosa of the carina is the most sensitive area of the trachea and larynx for triggering a cough reflex. Widening and distortion of the carina may be a serious sign because it always indicates carcinoma of the lymph nodes around the region where the trachea divides.

Complete answer:
The division of the trachea into the proper and left main bronchi; it occurs at the extent of the fifth or sixth thoracic vertebral body and is marked internally by the presence of a carina or keel-like ridge between the diverging bronchi.
In anatomy, the carina may be a ridge of cartilage within the trachea that happens between the division of the 2 main bronchi. The carina occurs at the lower end of the trachea (usually at the extent of the 4th to 5th thoracic vertebra). This is often in line with the sternal angle, but the carina may raise or descend up to 2 vertebrae higher or lower with breathing. The carina lies to the left of the midline, and runs antero-posteriorly (front to back). The bronchial arteries supply the carina and therefore the remainder of the lower trachea. The carina is round the area posterior to where the aorta crosses to the left of the trachea. The azygos vein crosses right to the trachea above the carina.

Note:
In a cadaver the extent of bifurcation of the trachea is at the lower border of the T4 vertebra, range is T3−T5. during a living person it varies from T5−T7 on a mean T6. The rationale for the shortening of tracheal length during a cadaver is thanks to tracheal muscle (trachealis) contraction.