Tiny hairs called cilia line the bronchus in the lungs and move microbes and debris up and out of the airways. Scattered throughout the cilia are goblet cells that secrete mucus which helps protect the lining of the bronchus and trap microorganisms. The trachea is also lined with cilia that move in rhythm to push mucus out of the trachea so that it can be expelled or swallowed. Mucus has an important role in the lungs immune response because it traps irritants in the airways and helps the body expel them through coughing. Pathogens and particles that are trapped on the mucus layer are coughed out or moved to the mouth and swallowed. In addition to cilia and mucus, the respiratory system has other defense mechanisms to clean and protect itself, such as alveolar macrophages that seek out deposited particles and bind to them.