The lungs are massive vessel-like organs in the chest cavity. They are the largest and most essential part of the respiration system. The air we breathe enters and exits our lungs through two passages; the bronchioles and the bronchi. Lungs’ main responsibilty is to take oxygen from the atmosphere and transport it into the bloodstreem. It then excretes carbon dioxide from blood into the atmoshpere. This gas exchange happens through specialized cells that form many millions of thin-walled air sacs. Some non-respiratory functions are also performed by the lungs.
In single celled bacteria and other small organisms, the respiration process of gas exhange can happen through simple diffusion. In large organisms, however, this is impossible, because a very small amount of cells in large organisms are located close enough to the surface for diffusion to take place. Two major changes made it possible for all organisms to attain multicellularity. One being an efficient circulatory system to transport gases to and from all tissues in the body. The other is a large respiratory system. The respiratory system centralizes the responsibilty of collecting oxygen from the atmosphere...
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