secretie

Secretie, or secretion, is the process by which living cells produce and release substances. Substances produced by secretory cells may be delivered to body surfaces or cavities via ducts (exocrine secretions) or released into the bloodstream (endocrine secretions). Common secretions include digestive enzymes, mucus, saliva, sweat, tears, and hormones.

Secretory products are typically synthesized in the secretory cells, sorted and packaged in the Golgi apparatus, and stored in secretory vesicles until release. Release is usually triggered by physiological signals such as hormones, neurotransmitters, or changes in ion concentrations and occurs by exocytosis, though some secretions involve shedding of cytoplasm or cell rupture. Secretory processes are commonly categorized as merocrine (vesicle-mediated exocytosis), apocrine (loss of a portion of the cell’s cytoplasm with the secretory product), and holocrine (disintegration of the entire cell).

Secretions are central to digestion (gastric juice, pancreatic enzymes), lubrication and protection of epithelial surfaces (mucus, saliva, tears, sweat), respiration (airway mucus), and reproduction (hormonal secretions). Dysregulation of secretion underlies various diseases, such as excessive secretions (rhinorrhea, diarrhea), insufficient secretions (dry mouth, dry eyes, pancreatic insufficiency), and conditions like cystic fibrosis or Sjögren's syndrome. The study of secretion informs physiology, medicine, and pharmacology, and measurement of secretions or their components is used in diagnostics.