The respiratory system consists of organs, passageways, and structures. Air enters the respiratory system through the nose or the mouth, which are organs. The air then passes through the pharynx at the back of the nose and mouth and into the larynx, or voicebox. The air travels from the larynx into the trachea, or windpipe. The pharynx and the trachea are often considered to be passageways. The larynx is classified as an organ.
The trachea transports the air into tubes called bronchi. These lead to the lungs, which are organs. Inside the lungs, the bronchi divide into narrower passageways called bronchioles, which transport the air to the alveoli, or air sacs, within the lungs.