When air is inhaled, dirt and other particles are trapped by tiny hairs and sticky fl uid in the nose.
The air flows into the throat and passes through the larynx. The larynx contains vocal cords that vibrate as the air moves through them. This produces the sound of your voice.
The air continues via a series of tubes that then connect the throat to the lungs.
These tubes become smaller and smaller as they travel deeper into the lungs which enable them to carry oxygen to all parts of the lungs.
Once air reaches the lungs, the exchange of gases occurs between the blood and the alveoli. These Alveoli are clusters of tiny air sacs in the lungs. The wall of each alveolus is a single layer of cells. Alveoli are surrounded by a network of tiny blood vessels called capillaries. The wall of each capillary also is a single layer of cells. Th e ultra-thin walls of both the alveoli and the capillaries allow the exchange of gases between the air and the blood, as shown in Figure 1.20. Once the air enters the capillaries, oxygen from the air is taken up by the red blood cells. Th e red blood cells are responsible for transporting gases in the bloodstream. Oxygen diffuses through the walls of the alveoli, through the capillary walls, and into the red blood cells. Th e blood also releases carbon dioxide into the lungs. Th e path that carbon dioxide follows is the reverse of the path that oxygen follows. Carbon dioxide diff uses from the blood through the capillary walls, through the walls of the alveoli, and into the alveoli. Once in the lungs, the carbon dioxide is exhaled with the next breath.
The upper-right chamber (right atrium) receives carbon dioxide-rich blood from the body.
The carbon-dioxide-rich blood moves into the lower-right chamber (right ventricle), which pumps it to the lungs. Inside the lungs, the blood gets rid of the carbon dioxide and picks up oxygen again. 3.  The upper-left chamber (left atrium) receives the oxygen rich blood from the lungs. 4.  The oxygen-rich blood moves into the lower-left chamber (left ventricle), which pumps it to the body cells.