What four basic features, common to all aerobic respiratory systems, must the human respiratory system possess in order to perform oxygen procurement and carbon dioxide elimination? What are the organs that possess these features; where are they located?
In order to perform these two functions, the human respiratory system: 1) must provide a large enough respiratory surface to take in enough oxygen for all the cells of an individual; 2) must provide a method of transporting gases between the area of exchange with the outside environment and the internal cells; 3) must protect the exchange surface from mechanical injury; and 4) must keep the exchange surface moist so that gases can diffuse into solution and be absorbed by the body. The lungs are the organ which possess these features. The two lungs are invaginated gas-exchange organs. Their highly subdivided inner surface has a surface area of over one hundred square meters (over fifty times the surface area of the body) and is highly vascularized. The lungs are located within the thoracic cavity and protected by the rib cage that delimits this cavity. The passageways leading to the lungs help moisten the air. This helps prevent the thin film of water that covers the lungs' inner surface, in which the gases dissolve, from drying out.
