According to The Columbia Encyclopedia, lungs are important because most vertebrate animals use them to breathe. The lungs provide the space for the exchange of gases that occurs alongside the action of breathing; this exchange consists of oxygen entering the body and carbon dioxide leaving it.
The Columbia Encyclopedia states that the only vertebrates that do not breathe through lungs are the majority of fish, which depend on gills to breathe, and a number of amphibian species that breathe through the skin. In humans, lungs take up much of the chest cavity, stretching from the collarbone to the diaphragm. Air enters the body through the nose or mouth and goes through the trachea to reach the two bronchi, which then enter one lung each. When blood flows through the capillaries in the lung, oxygen from the air in the lung diffuses into the bloodstream while carbon dioxide enters air sacs known as alveoli.
A number of diseases of the lung exist, interfering with the healthy function of organs that are essential to human survival and well-being, the Columbia Encyclopedia states. Lung cancer and emphysema, both of which are diseases caused by smoking, are well-known examples of lung disease. Viral infections cause pneumonia, while allergic responses trigger asthma attacks.