Overview of the Lungs
The lungs are part of the respiratory (breathing) system and are located in the chest, inside the rib cage and above the diaphragm. Lungs are complex organs that consist of spongy, elastic tissue that is designed for oxygen intake and the expiration of carbon dioxide.
Oxygen enters the lungs when we inhale a breath. It is distributed throughout the lungs by a system called the bronchial tree, with branches of decreasing diameter (called bronchi and bronchioles). The bronchial tree carries oxygen to small sacs (alveoli) deep within the lung where oxygen, from air that is inhaled, moves from the lung into the blood stream, and carbon dioxide, a byproduct of our metabolism, moves from the blood into the lung to be exhaled. Intake of oxygen and delivery by the blood to tissue is necessary for all of the cells in our body to function. Removal of carbon dioxide is necessary to maintain the blood's pH at an appropriate level as part of the body's system of acid-base balance.
Since the air we breathe contains many components from the environment such as dust, pollens, bacteria, viruses, smoke, and volatile chemicals, the lungs maintain a system of defense against these potentially toxic invaders. The lungs’ defense system includes immune cells and the secretion of mucus to contain and remove these unwanted components from the lungs.