Diffusion of oxygen from the blood into cells. Carbon dioxide follows a reverse path. Image from W.H. Freeman and Sinauer Associates, used by permission. This system includes the lungs, pathways connecting them to the outside environment, and structures in the chest involved with moving air in and out of the lungs. Image from W.H. Freeman and Sinauer Associates, used by permission.
Air enters the body through the nose, is warmed, filtered, and passed through the nasal cavity.
The vocal cords are two bands of tissue that extend across the opening of the larynx. After passing the larynx, the air moves into the bronchi that carry air in and out of the lungs. Images from W.H. Freeman and Sinauer Associates, used by permission. Bronchi are reinforced to prevent their collapse and are lined with ciliated epithelium and mucus-producing cells. Bronchi branch into smaller and smaller tubes known as bronchioles .