The cone-shaped lungs are sponge-like organs that fill the chest cavity and make up most of the lower respiratory tract. Their most important job is providing oxygen to capillaries so they can oxygenate blood.

Each lung is divided into lobes. The right lung has three, but the left lung has only two, thus allowing room to accommodate the heart.

Together, the lungs’ tissue surface is almost 40 times greater than the body’s outer surface, making the lungs (together) one of the largest organs in the body.

Each lung houses a bronchial tree, which gets its name from the intricate network of air passages that supply the lungs with air. The air-filled sacs in the lungs called alveoli resemble grape clusters. White blood cells known as macrophages, located inside each alveolus, ingest and destroy airborne irritants that enter the lungs. After you exhale, the lungs stay partly inflated because of a fluid called surfactant that is produced by special cells and secreted within the alveoli. Surfactant contains fatty proteins and helps to prevent lung infections.

Suffering from a respiratory disorder is one of the most common reasons for doctor visits in industrialized countries, where the air is filled with chemicals, pollutants, dust, pollen, bacteria, and viruses. The billions of microorganisms — bacteria, viruses, and fungi — in the air you breathe can enter the lungs, and they make respiratory infections quite common. Some infections, such as the common cold or sinusitis, affect the upper respiratory tract. Others, such as bronchitis and pneumonia, affect the lower respiratory tract.

Some respiratory disorders are:

  • Acute bronchitis: This develops suddenly and can occur as a complication of an upper respiratory tract infection, such as a common cold, usually caused by a virus.
  • Pneumonia: Pneumonia causes the smallest parts of the lungs (bronchioles and alveolar tissue) to become inflamed. Pneumonia can be fatal for elderly people, children, and others with lowered or weakened immune systems.
  • Asthma: Asthma attacks are caused by constricted airways. Allergic asthma—a type caused by allergens—often develops in childhood. The number of cases of childhood asthma continues to rise.
  • Tuberculosis: Tuberculosis is a contagious bacterial infection of the lungs. It continues to be a problem for people living in developing countries.