Chapter 12 - Exocrine Glands
Exocrine glands secrete their products onto the surface of an epithelium.
Exocrine glands can be classified in various ways:
- Organization - unicellular or multicellular
- Structural - nature of the duct system (simple or compound) and shape of secretory units (tubular, acinar (or alveolar), tubuloalveolar)
- Product secreted - serous (proteins), mucous (mucus) or mixed seromucous
- Mode of secretion - merocrine (exocytosis), holocrine (apoptosis) or apocrine
Unicellular exocrine glands release their products from epithelial cells specialized for secretion directly onto the surface of an epithelium (e.g., goblet cells in the intestinal and respiratory epithelium).
Multicellular exocorine glands are clusters of secretory cells that release their products through a duct onto the surface of an epithelium.
Examples of multicellular exocrine glands include the salivary glands, sweat glands, sebaceous glands, pancreas, and mammary glands. The salivary glands and exocrine pancreas are examined in this chapter.
The salivary glands secrete saliva that aids mastication, effective swallowing, and digestion. These glands contain two types of cells:
- Serous cells - secrete a protein-rich fluid
- Mucous cells - secrete highly-glycosylated proteins called mucins (mucins bound by water are known as mucus)
The major salivary glands differ in their secretions:
- Parotid glands - almost entirely serous cells
- Submandibular glands - mostly serous cells (95%), some mucous cells (5%)
- Sublingual glands - mostly mucous cells (65%), some serous cells (35%)
Salivary glands are compound tubuloalveolar in structure.
The pancreas is the largest exocrine gland and is 95% exocrine tissue and 1-2% endocrine tissue. The exocrine portion is a purely serous gland which produces digestive enzymes that are released into the duodenum. The duct cells also secrete bicarbonate to neutralize acid from the stomach.
The exocrine pancreas is compound tubuloacinar in structure. Centroacinar cells are epithelial cells from the beginning of ducts that protrude into the acinar lumen.
The blood supply to exocrine glands can be seen after perfusion with a colored dye.