The trachea ultimately divides into

The trachea ultimately divides into two smaller tubes called bronchi, one is going to each lung. The bronchi divide into tiny passage-ways that are named bronchioles, which lead directly to minute air sacs, or alveoli. The exchange of life-giving gases is effected through the walls of the alveoli.
Mechanisms in the upper respiratory tract serve to filter, and warm the air in its journey to the lungs. The hairs, or cilia, in the nostrils partially filter out dust particles as does sticky secretion called mucus, which has been produced by mucous cells lining the mouth, nasal passages, pharynx and trachea. Cilia in the nasal passages and trachea are effective in helping to remove foreign particles from the upper respiratory tract.
Other structures connected with the system include: the laryngeal tonsils, which are masses of tissue in the nasopharynx or posterior portions of the nasal passages (adenoids are infected or diseased laryngeal tonsils); the sinuses, cavities in the bones in the front part of the skull that provide resonance to the voice, and the pleura, which is a double-walled membrane surrounding the lungs.
The diaphragm contracts and flattens, contributing to the extension of the vertical diameter of the thoracic cavity and raising the ribs. Air is constantly renewing in the lungs. The capacity of the air passages is increasing. Any muscular effort, e.g. even standing up, increases the number of respirations.