The respiratory system's primary function is to supply the blood with oxygen and remove carbon dioxide. It does this through breathing, which involves inhaling oxygen and exhaling carbon dioxide through the nasal cavity, pharynx, larynx, trachea, bronchial tubes, and lungs. Diseases of the respiratory system include asthma, bronchitis, pneumonia, and lung cancer. Antibiotics, antihistamines, and decongestants are common drugs used to treat respiratory infections.