gets oxygen from the air into the blood via the lungs. It consists of the nose, throat, trachea (windpipe), and lungs. As you inhale (breathe in) you draw in fresh air. As you exhale (breathe out), you expel stale air from the lungs. Deep in the lungs, in air pockets called alveoli, the air is brought into very close contact with blood passing through tiny blood vessels. This process allows oxygen, which is vital for cellular respiration to pass from the lungs into the blood. It also allows the waste product carbon dioxide to pass from the blood to the lungs, and then out into the air. If carbon dioxide were allowed to accumulate in the body, it would be poisonous.