mucussecretion

Mucussecretion is the physiological process by which mucus is produced and released by goblet cells and mucous glands in the mucous membranes of the respiratory, gastrointestinal, and other tracts. Mucus is a viscoelastic gel that combines water, electrolytes, lipids, and glycoproteins called mucins. In humans, the major mucins in airway mucus are MUC5AC and MUC5B, while intestinal mucus contains MUC2; the gel also contains secretory IgA, antimicrobial peptides, and enzymes. The mucus layer overlays a hydrated periciliary layer and supports mucociliary clearance.

Secretion occurs through exocytosis of mucin-containing granules from goblet cells and glandular acini. Secretion is normally constitutive but can be rapidly stimulated by neural (acetylcholine, vagal input), hormonal, and inflammatory signals. Inflammation or infection commonly increases goblet cell numbers and mucus production, altering mucus composition and viscosity.

The primary functions of mucussecretion are to hydrate and lubricate surfaces, trap inhaled particles and pathogens, and facilitate their removal by ciliary action or flushing. In the respiratory tract, mucus interacts with cilia to move toward the pharynx; in the gastrointestinal tract mucus protects epithelia and supports barrier function.

Clinical relevance: abnormal mucussecretion contributes to disease. Hypersecretion occurs in infections, allergic rhinitis, asthma, and chronic bronchitis; mucus can become thick and tenacious, leading to plugging. In cystic fibrosis, altered ion transport dehydrates mucus, increasing viscosity. Analyses of mucus and mucin gene expression (e.g., MUC5AC, MUC5B, MUC2) have research and diagnostic value.