Clearance mechanism in the airways that moves bronchial mucus upward toward the oropharynx; propulsion of mucus is provided by the rhythmic beating action of cilia, which contact, stretch and push forward bronchial mucus, thus overcoming its natural viscosity. SYN: ciliary transport mechanism. Once in the oropharynx, mucus may be swallowed or sneezed or coughed out. SEE ciliary transport mechanism, oropharynx.