Lungs are vital organs of the body. There are two lungs - right lung and left lung. There are three separate sealed compartments in your chest: one for right lung, one for heart and one for left lung. Both the  lungs hang loose inside the chest filling it completely. Each lung weighs about 500 gms. Lungs have no muscles. They play a passive role in breathing.

You look to your wind pipe. Wind pipe is about 10 cm long. Wind pipe divides into two at its lower end to two main bronchial tubes- one for right lung and the other for left lung. Then these two bronchi branch out like an upside-down banyan tree. The branches which are about 1/40th of a centimetre in diameter are called bronchioles. These bronchi and bronchioles are really air passages. Real work of respiration which the lung does, is done by its alveoli. Alveoli are grape like bunches of air sacs. Flattened out, and joined together all alveoli will cover half of a tennis court.

Each alveolus is covered by a cobweb of capillaries. Blood is pumped by the heart into the end of a capillary. Red blood cells (R.B.C.S.) pass through the capillary one by one in single-file. The passage takes about one second. There the most remarkable miracle takes place. Through the membrane of the capillary wall, the cells diffuse the carbon dioxide into the alveoli. At the same time, the cells take of oxygen. This is known as gas exchange. Blue impure blood in one end of capillary, emerging refreshed like ripe tomato juice at the other end. This entire process gives life.

If you smoke, or move in polluted environment the lungs get diseases.