Lungs 101 | National Geographic

• [Narrator] Breathe in, breathe out. With every breath, the body is replenished and cleansed. A process made possible by two of the body's most important and delicate organs.

The lungs are two major components of the respiratory system. Soft, light, and elastic, these organs are prime for taking in and filling up with air. Each lung is subdivided into compartments called lobes. The right lung has three, and the left lung, which is slightly smaller to accommodate the positioning of the heart, has two.

This compartmentalization provides a fail-safe for the lungs, so that if one lobe is damaged, the four other lobes may remain intact and able to function. The lobes are also connected to separate branches, called bronchi, of the trachea, which delivers air from the nose and mouth. These branches provide the lobes independent supplies of air.

Within each lobe, the bronchi split off into numerous smaller offshoots that end in air sacs. Known as alveoli, these sacs are responsible for a crucial exchange of air. When a person inhales, oxygen fills the alveoli. The alveolar walls, which contain countless capillaries, are so thin that the oxygen inhaled can pass through them and be absorbed by blood cells within the capillaries.

A similar transaction occurs in the opposite direction. Carbon dioxide waste transported in the bloodstream can pass through the alveolar walls. From there, they are expelled with every exhalation. This exchange of gases, known as respiration, is what gives the respiratory system its name.

Because of their intake of air, the lungs are constantly exposed to the elements, and sometimes fall victim to them. Lung conditions may develop, such as emphysema, which for some is caused by the inhalation of tobacco smoke. And pneumonia, which can be caused by the inhalation of infectious organisms.

All together, these and other lung diseases are the fourth-leading cause of death in the United States. The lungs are delicate organs. But despite their vulnerability, their anatomical design allows them to stay strong and play a vital role in fueling the body.