• The lungs are a vital part of the respiratory system.Dynamic Graphics/Dynamic Graphics Group/Getty Images
  
  Encased within the rib cage, the lungs are a pair of organs that provide the body with oxygen. A critical part of the respiratory system, the lungs enable "the exchange of carbon dioxide and oxygen between the circulating blood and the atmosphere," according to the Merck Manuals. The lungs, often depicted as two pink balloons, are much more complex than simply functioning as sacks of air.
  
  

Lobes

• Each lung is divided into sections called lobes. The superior, middle and inferior lobes comprise the right lobe. To make room for the heart, the left lung is slightly smaller than the right lung; the left lung has only two lobes: superior and inferior. Because each lobe is separate from the others, should one become damaged, it can be removed without damage to the remaining lobes.
  
  

Bronchial Tubes and Bronchioles

• The bronchial tubes are airways that lead from the trachea to the lungs. They branch out from the trachea into the lungs, and then branch further into smaller passages called bronchioles. Bronchioles control air distribution and flow in the lungs.
  
  

Alveoli and Capillaries

• At the end of each bronchiole is a tiny sac called an alveolus. According to WebMD, the human body contains 300 million alveoli. Alveoli are covered in very small vessels called capillaries. Oxygen is absorbed into the blood through alveoli walls; this oxygenated blood then travels to the heart. Oxygen is then distributed to all tissue and organ cells. With the use of this oxygen, these cells produce carbon dioxide, which travels to the lung capillaries and is then expelled from the body during exhalation.