Like that of the tongue, cell receptors in the lungs can detect bitter substances. "Epithelial cells that line the airways in the lungs use the same type of sensory receptors" as found in the tongue and act to repel bitter compounds which are often toxic. "Tiny, hair-like projections called cilia" do the work of both sensing these invaders and expelling them at the same time.
"Such offending substances could include irritants like cigarette smoke, or molecules that activate bitter receptors such as those that are generated, for instance, by the infectious microorganism Pseudomonas aeruginosa. The research also revealed that cells in the lungs and the tongue rely on the same signaling molecules to transform the detection of a bitter compound into a response – either the beating of the motile cilia in the lungs or the generation of a nerve impulse in the tongue."