The inhaled air travels from nostril to pharynx. From pharynx it enters into larynx. The epiglottis acts as a lid due to which air enters the trachea and not into the alimentary canal. The trachea thus provides a clear airway for air to enter into 2 large tubes called bronchi which leads to one of the lungs. The bronchi divide into bronchioles which further divide into alveoli. Gas exchange takes place here in alveoli.