Exocrine Glands: Unicellular and Multicellular Glands

Unicellular exocrine glands are individual secretory cells, such as goblet cells in the intestinal epithelium, that directly secrete mucin onto epithelial surfaces. Multicellular exocrine glands consist of groups of cells forming secretory units with ducts that deliver secretions to the surface. Multicellular glands are more complex and can be further classified based on duct and secretory unit morphology.

Multicellular exocrine glands are classified as simple glands with unbranched ducts or compound glands with branched ducts. Simple glands have a single continuous duct, while compound glands have multiple branched ducts that deliver secretions from various secretory units to the epithelial surface.

Tubular glands contain secretory units shaped as straight or coiled tubes. Examples include intestinal glands and sweat glands, which are simple tubular glands with a single duct, and gastric glands, which are simple branched tubular glands. Compound tubular glands are found in organs like the testes and male reproductive system.

Alveolar or acinar glands have secretory units shaped as hollow sacs, unlike tubular glands with tube-shaped units. Sebaceous glands are simple branched alveolar glands, while mammary glands are compound alveolar glands with secretory sacs connected to branched ducts. Some glands like salivary glands contain both tubular and alveolar sacs.

Goblet cells are unicellular exocrine glands that secrete mucin, a complex glycoprotein, onto the epithelial surface of the small and large intestines. This mucin forms a slimy protective mucus coat that lubricates and protects the intestinal lining from mechanical damage and pathogens.

Compound tubuloalveolar glands contain both tubular and alveolar secretory sacs connected to branched ducts, combining features of both gland types. Salivary glands exemplify this structure. This mixed morphology allows these glands to produce diverse secretions more efficiently than glands with only one secretory unit type.

Ducts in multicellular exocrine glands transport secretions produced by secretory units to the epithelial surface or organ lumen. The duct structure—whether simple and unbranched or compound and branched—determines how efficiently secretions are delivered and influences the gland's overall secretory capacity and function.