Respiration is the process of obtaining and using oxygen, while eliminating carbon dioxide. It is the process by which human beings take in oxygen from their environment and give out carbon dioxide that is produced as a result of some chemical changes within the cells. The requirement of oxygen is indispensable for the human body. If the intake of oxygen is completely suspended for more than four minutes, the person usually dies. So, our body needs a continuous supply of oxygen . Some chemical changes take place in tissue cells. The main product of these chemical changes is CO2 . A continuous elimination of CO2 is essential. In fact, respiration is a twofold process. One is called internal respiration and the other is external respiration . The inhalation of oxygen is followed by some chemical changes in which , waste products are formed . Then exhalation of waste products takes place. The process of inhalation of O2 and exhalation of CO2+ H2O is called respiratory process . There are various organs of respiratory system , which play a vital role in respiration . These are mentioned below.