Mucous membranes line all of the bony surfaces of the sinus cavities. The lining is similar to the surface lining of the nasal passageways and airways of the lungs. The surface of this membrane is lined with microscopic cilia. These constantly moving hairs sweep mucus from the sinus cavities into the nasal passageway. Cells in mucous membranes manufacture mucus and proteins important in defense against bacteria, viruses, fungi, allergens and a variety of irritant particulates.
Mucus is a clear slippery fluid that coats the respiratory membranes of the sinuses, nose and lungs. Mucus consists of water, blood cells, digestive enzymes, salt, antibodies, dead cells, bacteria and other microorganisms and foreign pollutants.