ABSTRACT
The epithelial mucosa of the alimentary, respiratory, and reproductive tracts of mammals is covered by an extracellular and renewable layer of viscous mucus. This mucous layer consists of glycoproteins, proteins, and lipids in the form of a gel imbibed with water and electrolytes. The chapter provides information on lipids of mucous secretions in health and disease, and their role in the protection of underlying mucosa. The secretion of submandibular glands, which contains the products of mucous cells, is a complex mixture of cations, anions, nonelectrolytes, proteins, lipids, and glycoproteins. The lipids of submandibular saliva consist primarily of neutral lipids and glyceroglucolipids, and of lesser quantities of phospholipids. Analyses of chloroform/methanol extracts of mucus derived from alimentary and respiratory tracts indicate that lipids constitute 12.5% dry weight of the tracheobronchial mucus, 26 to 29% of the gastric mucus, and up to 40% of the intestinal mucus. Considerable quantities of lipids are also present in gastric and submandibular secretions.
