Secretory

Secretory refers to the production and release of substances by cells or glands. In biology, secretory processes move molecules such as enzymes, hormones, mucus, or sweat from the cell to the extracellular space or body fluids.

Secretory pathways begin in the endoplasmic reticulum with the synthesis of nascent proteins or lipids, transit through the Golgi apparatus, and packaging into secretory vesicles, which are directed to the plasma membrane for release by exocytosis. Secretory activity is categorized as constitutive secretion, which delivers materials continuously, and regulated secretion, which stores products in vesicles until a specific signal triggers release.

Secretory cells are specialized for production and discharge of specific substances. Goblet cells produce mucus; pancreatic acinar cells secrete digestive enzymes; mammary alveolar cells synthesize milk; endocrine cells release hormones into blood; neurons and neuroendocrine cells secrete neurotransmitters or neuropeptides.

Secretory products include digestive enzymes (amylase, proteases, lipases), mucus, hormones (insulin, adrenaline), neurotransmitters (acetylcholine, dopamine), sweat, bile acids, and milk proteins.

Mechanisms involve vesicle trafficking and fusion mediated by SNARE proteins, calcium signaling for regulated secretion, and polarity cues in epithelial cells that separate apical and basolateral secretory routes.

Clinical relevance: defects in secretory pathways can lead to disorders such as cystic fibrosis, which impairs mucus clearance; secretory diarrhoea due to dysregulated ion transport; exocrine pancreatic insufficiency; some neuroendocrine tumors alter secretory hormone release.