Mucus is a protective substance that's excreted from multiple areas of the body, such as the mouth, sinuses, throat, lungs, stomach, and intestines (Figure 1). Mucus itself consists of multiple constituents, but its major component is a substance called mucin.

Where is mucous found?

Mucous membranes line many tracts and structures of the body, including the mouth, nose, eyelids, trachea (windpipe) and lungs, stomach and intestines, and the ureters, urethra, and urinary bladder.

Is mucus found in the lungs?

Mucus is secreted from two distinct areas within the lung tissue. In the surface epithelium, which is part of the tissue lining of the airways, there are mucus-producing cells called goblet cells. The connective tissue layer beneath the mucosal epithelium contains seromucous glands which also produce mucus.