 
Your lungs are the pair of spongy, pinkish-gray organs in your chest. Air enters your lungs, and oxygen from that air moves to your blood. At the same time, carbon dioxide, a waste gas, moves from your blood to the lungs, and is exhaled.This process, called gas exchange, is essential to life. In your body, the muscles which cause the diaphragm to move up and down are controlled automatically by your nervous system; you don't have to think about it. 
Your diaphragm is a flat tissue below your lungs that moves up and down as muscles contract and expand. When your muscles pull it down, the chest cavity becomes larger, and the air pressure lowers. This causes your lungs to expand, all by themselves, as they fill with outside air. You're inhaling. When the muscles relax, the chest cavity decreases in size, and the air pressure inside the chest rises. This squeezes the lungs, forcing the air up and out. You're exhaling. The lungs are most important component of your respiratory system. Your respiratory system also includes the trachea (windpipe), muscles of the chest wall and diaphragm, blood vessels, and other tissues. All of these parts make breathing and gas exchange possible. Your brain controls your breathing rate (how fast or slow you breathe), by sensing your body’s need to get oxygen and also get rid of carbon dioxide. 
As air enters your trachea, it reached the bronchi, where it can go to both lungs. It eventually travels down narrower tubes called bronchioles, and into many alveoli. These tiny capsules are where the gases are exchanged: CO2 from veinous capillaries to the air, and O2 from the air into arterial capillaries. The air is now expelled from the lungs as you exhale. Not all of the oxygen was used; the air you breathed in was 21% oxygen. After the gas exchange, the air you breathe out is still 16% oxygen! This is why CPR works.  Anything that gets breathed into your lungs may get trapped. Asbestos fibres trapped in the lungs have been shown to cause cancers. So has cigarette smoke.The picture at the left shows the lungs of someone who has been a smoker for many years. Second hand smoke does the same to someone living in the household of a smoker. |