Exocrine gland

Definition

A gland that secretes its products through a duct onto an external or internal epithelial surface, rather than releasing them directly into the bloodstream or hemolymph. In arthropods, exocrine glands are structurally diverse and perform specialized functions including chemical communication, defense, silk production, and digestive enzyme delivery. These glands may be unicellular (such as scattered goblet cells) or multicellular with complex duct systems, and they discharge via merocrine, apocrine, or holocrine mechanisms depending on whether the secretory cell remains intact, loses its apical portion, or undergoes complete disintegration during secretion.

Etymology

From Greek exo- (outside) + krinein (to separate), referring to external secretion via ducts; contrasted with endocrine (endo-, within).

Example

The silk glands of larval Lepidoptera are large, paired exocrine glands that discharge through spinnerets to produce silk for cocoon construction; in social Hymenoptera, the Dufour's gland and venom gland are modified exocrine structures that secrete pheromones and defensive compounds through the sting apparatus.

Synonyms

• duct gland

Related Terms

• Endocrine gland
• holocrine
• merocrine
• apocrine
• pheromone gland
• silk gland
• venom gland
• Morphology
• epithelium

Usage Notes

The exocrine/endocrine distinction is functional rather than strictly anatomical—some glands, such as the arthropod mandibular glands, may have dual or shifting roles. In insect taxonomy, exocrine gland morphology (e.g., the structure of abdominal scent glands in Heteroptera) is often diagnostic at family or genus level. The term is sometimes used loosely for any secretory structure with a visible duct, though strict usage reserves it for epithelial-derived glands with defined secretory and duct regions.