Air enters the respiratory system through the mouth or nose. These two pathways merge at the pharynx, which is also the path for food moving to the esophagus. The epiglottis lies at the top of the larynx, and by folding during swallowing, it prevents food from entering the respiratory passages. Air moves through the larynx into the trachea, which is stiffened by rings of cartilage. The trachea divides into two bronchi that enter the lungs.
