exokrinen

Exokrinen (exocrine) denotes glands and secretions that discharge onto an epithelial surface through ducts, in contrast to endocrine glands that release hormones directly into the bloodstream. The term derives from Greek exo- “outside” and krinein “to secrete,” highlighting the external or luminal destination of the secretions.

Exokrinen glands are widespread and vary in structure. Classic examples include salivary and lacrimal glands that produce mucus and enzymes for digestion and ocular lubrication, sweat glands that secrete fluid for thermoregulation, and mammary glands that discharge milk. The pancreas is a notable organ with both exocrine and endocrine functions: its exocrine portion releases digestive enzymes and bicarbonate into the duodenum via the pancreatic duct, while the endocrine portion secretes hormones such as insulin and glucagon into the blood. The liver contributes to exocrine function through bile secretion into the gastrointestinal tract.

Secretion mechanisms include merocrine (exocytosis of vesicles), apocrine (loss of a portion of the cell apical cytoplasm), and holocrine (cell rupture). Exokrinen products may be enzymes, mucus, or fluids that function in digestion, lubrication, protection, or thermoregulation. Regulation involves neural input and hormones; for example, secretin stimulates pancreatic bicarbonate‑rich juice, while cholecystokinin stimulates enzyme‑rich secretions.

Pathologies may affect exokrinen glands or ducts, such as exocrine pancreatic insufficiency in cystic fibrosis, chronic pancreatitis, or ductal obstruction. Exokrinen glands can be studied histologically by identifying acinar or tubuloacinar units and the ductal network.