Respiratory Diseases Respiration is the process of taking in and using oxygen. There are three different phases of respiration: external respiration, internal respiration, and cellular respiration. External respiration is the intake of oxygen from the environment and the release of carbon dioxide. In internal respiration, oxygen is carried to the cells and carbon dioxide is carried away from the cells. In cellular respiration, oxygen is used in chemical reactions within the cells. Some Diseases of the respiratory system are: bronchial asthma, the common cold, and diphtheria.