In
vertebrates,
mucus ( ;
adjectival form: "mucous") is a slippery secretion produced by, and covering,
mucous membranes. Mucous fluid is typically produced from cells found in mucous glands. Mucous cells secrete products that are rich in
glycoproteins and water. Mucous fluid may also originate from mixed glands, which contain both
serous and mucous cells. It is a
viscous colloid containing
antiseptic enzymes (such as
lysozyme),
immunoglobulins,
inorganic salts, proteins such as
lactoferrin, and
glycoproteins known as
mucins that are produced by
goblet cells in the mucous membranes and
submucosal glands. This mucus serves to protect
epithelial cells (the lining of the tubes) in the
respiratory,
gastrointestinal,
urogenital, visual, and auditory systems in
mammals; the
epidermis in
amphibians; and the
gills in
fish. A major function of this mucus is to protect against
infectious agents such as
fungi,
bacteria and
viruses. The average human nose produces about a litre of mucus per day. Much more mucus is produced in the gastrointestinal tract.
