Mucins: High molecular weight mucoproteins that protect the surface of EPITHELIAL CELLS by providing a barrier to particulate matter and microorganisms. Membrane-anchored mucins may have additional roles concerned with protein interactions at the cell surface.Gastric Mucins: Mucins that are found on the surface of the gastric epithelium. They play a role in protecting the epithelial layer from mechanical and chemical damage.Mucin-5B: A gel-forming mucin that is predominantly expressed by submucosal glands of airway tissues and the SUBLINGUAL GLAND. It is one of the principal components of high molecular weight salivary mucin.Mucin-1: Carbohydrate antigen elevated in patients with tumors of the breast, ovary, lung, and prostate as well as other disorders. The mucin is expressed normally by most glandular epithelia but shows particularly increased expression in the breast at lactation and in malignancy. It is thus an established serum marker for breast cancer.Mucin-4: A transmembrane mucin that is found in a broad variety of epithelial tissue. Mucin-4 may play a role in regulating cellular adhesion and in cell surface signaling from the ERBB-2 RECEPTOR PROTEIN-TYROSINE KINASE. Mucin-4 is a heterodimer of alpha and beta chains. The alpha and beta chains result from the proteolytic cleavage of a precursor protein.Mucin-3: A membrane-bound mucin subtype that is primarily found in INTESTINAL MUCOSA. Two closely-related subtypes of this protein have been identified in humans.Mucin-6: A gel-forming mucin that is predominantly associated with the gastric epithelium.Goblet Cells: A glandular epithelial cell or a unicellular gland. Goblet cells secrete MUCUS. They are scattered in the epithelial linings of many organs, especially the SMALL INTESTINE and the RESPIRATORY TRACT.Mucus: The viscous secretion of mucous membranes. It contains mucin, white blood cells, water, inorganic salts, and exfoliated cells.Sialomucins: A subcategory of mucins that contain SIALIC ACID.Glycosylation: The chemical or biochemical addition of carbohydrate or glycosyl groups to other chemicals, especially peptides or proteins. Glycosyl transferases are used in this biochemical reaction.Antigens, Tumor-Associated, Carbohydrate: Carbohydrate antigens expressed by malignant tissue. They are useful as tumor markers and are measured in the serum by means of a radioimmunoassay employing monoclonal antibodies.Oligosaccharides: Carbohydrates consisting of between two (DISACCHARIDES) and ten MONOSACCHARIDES connected by either an alpha- or beta-glycosidic link. They are found throughout nature in both the free and bound form.Trachea: The cartilaginous and membranous tube descending from the larynx and branching into the right and left main bronchi.Periodic Acid-Schiff Reaction: A histochemical technique for staining carbohydrates. It is based on PERIODIC ACID oxidation of a substance containing adjacent hydroxyl groups. The resulting aldehydes react with Schiff reagent to form a colored product.Carbohydrates: The largest class of organic compounds, including STARCH; GLYCOGEN; CELLULOSE; POLYSACCHARIDES; and simple MONOSACCHARIDES. Carbohydrates are composed of carbon, hydrogen, and oxygen in a ratio of Cn(H2O)n.Intestinal Mucosa: Lining of the INTESTINES, consisting of an inner EPITHELIUM, a middle LAMINA PROPRIA, and an outer MUSCULARIS MUCOSAE. In the SMALL INTESTINE, the mucosa is characterized by a series of folds and abundance of absorptive cells (ENTEROCYTES) with MICROVILLI.Carbohydrate Sequence: The sequence of carbohydrates within POLYSACCHARIDES; GLYCOPROTEINS; and GLYCOLIPIDS.Conjunctiva: The mucous membrane that covers the posterior surface of the eyelids and the anterior pericorneal surface of the eyeball.