The respiratory system is responsible for breathing and gas exchange. It includes the nose, sinuses, mouth, larynx, epiglottis, trachea, lungs, diaphragm and alveoli. The nose and sinuses warm, clean and humidify inhaled air using hairs called cilia and mucus. Air then travels through the trachea to the lungs where oxygen and carbon dioxide are exchanged in alveoli before being transported by red blood cells. The diaphragm and rib muscles help breathing by expanding the lungs. Coughing, sneezing and yawning help clear the respiratory tract. Diseases like pneumonia, bronchitis and lung cancer can affect the lungs.