The respiratory bronchioles open into the alveolar ducts, alveolar sacs, and alveoli. Air then travels down the pharynx, through the trachea, and into the lungs.

In the lungs, air passes through the branching bronchi, reaching the respiratory bronchioles, which house the first site of gas exchange. These include the hair and mucus in the nasal cavity that trap dust, dirt, and other particulate matter before they can enter the system.

respiratory bronchiole — terminal portion of the bronchiole tree that is attached to the terminal bronchioles and alveoli ducts, alveolar sacs, and alveoli. particulate matter — small particle such as dust, dirt, viral particles, and bacteria that are in the air. pharynx — throat; a tube that starts in the internal nares and runs partway down the neck, where it opens into the esophagus and the larynx. mucus — sticky protein-containing fluid secretion in the lung that traps particulate matter to be expelled from the body.