In, out, in, out -- The respiratory system -- Nose and throat -- Looking at the lungs -- Breathing in -- Breathing out -- Controlling respiration -- Lung defenses -- Breathing faster and slower -- Making noises -- Absorbing area -- Gas exchange -- Gases in the blood -- Cellular respiration -- Energy factories -- Lung problems -- Problems caused by the environment -- Improving the lungs -- Breathing at great heights -- Breathing underwater -- Healthy lungs.