The lower respiratory tract contains all of the respiratory structures inferior to the larynx, which includes the:
Like the upper respiratory tract, the lower tract also functions to conduct air into and out of the lungs. In the lower respiratory tract, the air flows from the trachea through the bronchial tree of the lungs to the alveoli. The tree and its associated parts allow for gas exchange. While gas exchange is the primary function of the respiratory system, it only occurs in the lower respiratory tract.
Figure 1: The lower respiratory tract and the diaphragm.