And the mucus membrane is secreted and created by specialized cells known as goblet cells. Now, as the air travels through our nasal cavity, the pollutants and bacterial cells and other harmful substances essentially get stuck within this mucus membrane. So we see that the nasal cavity, because it contains these tiny extensions known as cilia, as well as a mucus membrane that helps trap this harmful substance, the nasal cavity actually functions in the process of filtering. It helps our immunity system. It helps protect our lungs from different types of harmful agents. Now, once our air passes through the nasal cavity, it enters a region, a passageway known as our pharynx.