The primary purpose of the respiratory system is to bring oxygen to the lungs and remove any unnecessary gases. Oxygen is important for mammal. All animals have a mechanism that exchange of gases. Mammals have windpipe to bring oxygen to lungs.
Respiratory system brings in oxygen through the mouth or nose. As air is breathed in, it passes through the back of the nose where dust and gases are filtered. When you breathe out, carbon dioxide is released. But plants inhale carbon dioxide and exhale oxygen. Plant is important for our envilonment.
Birds need a tremendous amount of oxygen to gain energy for flight, so they have developed a different respiratory system. They have a air sacs which are like tiny air bags in cars. The process of oxygen circulating through the body in birds is done through small blood vessels.
There are two important components of respiratory system that do not have anything to do with breathing. One is to bring liquids and food to the proper location in your body. The second function relates to smell and connects to our nose. All of these respiratory functions working together are just one part of our amazing body.