Final answer:
The statement about the trachea is false as the carina and bifurcation of the trachea are generally at the level of the fourth to sixth thoracic vertebrae and in line with the angle of Louis and the second costal cartilage.
Step-by-step explanation:
The statement that the trachea extends until it splits into the mainstem bronchi at the carina, which is at the level of the fifth thoracic vertebrae, the second costal cartilage, and externally at the angle of Louis, is false. The trachea indeed branches into the right and left primary bronchi at the carina, and this occurs generally around the level of the fourth to sixth thoracic vertebrae; however, the anatomical landmark that corresponds to the carina and the bifurcation of the trachea is usually at the level of the sternal angle (angle of Louis), which is in line with the second rib and hence the second costal cartilage. Therefore, the premise that this occurs at the level of the fifth thoracic vertebrae is incorrect.
The bronchial tree begins with the branching of the trachea into the primary bronchi. The primary bronchi then enter the lungs at the hilum, where they continue to branch into secondary and tertiary bronchi, and eventually into bronchioles and alveoli. The main function of the bronchi is to facilitate the passage of air into and out of the lungs, and the mucous membranes lining the bronchi also trap debris and pathogens.