Question 24

College Answer

To pass this question, the following were required for each section (trachea and main bronchi): 
landmarks; basic structural anatomy; and important relations (major vessels; major nerves; 
major structures). 
Marks were also allocated for innervation, and blood supply and venous drainage of the 
trachea.
Most unsuccessful answers did not address a number of these areas. Overall, the answers 
were better for tracheal anatomy compared to bronchial anatomy. 
A structured approach to anatomy questions works well and this was again the case (i.e. 
relations / blood supply / etc.

Discussion

Most of the college answer appears to be concerned with details which can be found in Lasts's Anatomy, Regional and Applied. That is where this answer has come from. More detail and an extensive bibliography of irrelevant references can be found in the chapter on the structure and function of the lower airway. Judging by the examiner's comments, a pass-level answer for this question would contain the following details:

The trachea:

• 10cm fibrocartilaginous tube stretching from C6 to the sternal angle
• Lined with pseudostratified columnar ciliated epithelium and goblet cells
• Superiorly, bordered by the larynx
• Posterior relation: oesophagus
• Right lateral relations:  pleura, lung, and the vagus nerve; azygous vein inferiorly
• Left lateral relation: left common carotid and subclavian arteries, arch of the aorta, left recurrent laryngeal nerve
• Anterior relations: skin and thyroid superiorly, SVC 
• Inferior relations: right pulmonary artery
• Supplied by the inferior thyroid and bronchial arteries; veins drain to the inferior thyroid plexus.
• Innervated by the vagus and T2-6 sympathetic chain

The bronchi:

• Dichotomously branching divisions of increasingly smaller tubes, consisting of complete and incomplete cartilaginous rings as well as smooth muscle
• The left main bronchus is longer, runs more horizontally and is about twice as long as the right main bronchus.
• Supplied by ​​bronchial arteries  and pulmonary circulation
• Venous drainage of the right main bronchus is into the azygos vein, and the left main bronchus drains into the accessory hemiazygos vein.
• Innervated by the vagus and T2-6 sympathetic fibres