Oral Histology: Salivary Glands

Salivary Glands

• Salivary glands are exocrine glands whose secretions flow into the oral cavity.
• There are three pairs of major salivary glands: parotid, submandibular, and sublingual, located outside the oral cavity, with ducts that discharge their secretions into the oral cavity.
• Minor salivary glands are located in various parts of the oral cavity, typically in the submucosal layer, with short ducts opening directly onto the mucosal surface.

Structure of Salivary Glands

• The parenchymal elements of the glands are derived from the oral epithelium and consist of terminal secretory units leading into ducts that mainly open into the oral cavity.
• The connective tissue (C.T.) forms a capsule around the gland and extends into it, dividing groups of excretory units and ducts into lobes and lobules.
• The C.T. contains blood and lymph vessels and nerves that supply the gland.

Functions of Salivary Glands

• The production and secretion of saliva is the most important function of salivary glands.
• Saliva contains various organic and inorganic substances that provide primary natural protection for the teeth and soft tissues of the oral cavity.

Composition of Saliva

• Saliva is a complex fluid comprising approximately 99% water.
• Organic constituents of saliva include enzymes (amylase, ribonuclease, kallikrein, esterase, histatin, cystatin, and peroxidase), immunoglobulins (IgG and IgM), and other factors like blood clotting factors, amino acids, urea, uric acid, and glucose.
• Electrolytes present in saliva include Na, Ca, Cl, HCO3, and HPO4, as well as Mg, SO4, F, ScN, and I in smaller concentrations.

Cell Types in Salivary Glands

• Serous cells: specialized for synthesizing, storing, and secreting proteins, with a pyramidal shape and a broad base adjacent to the C.T. stroma and a narrow apex forming part of the lumen of the end piece.
• Mucous cells: similar to serous cells, but with a larger lumen and producing secretions with little or no enzymatic activity, serving mainly for lubrication and protection of oral tissues.
• Myoepithelial cells (basket cells): contractile epithelial cells with no secretory function, supporting secretory units and facilitating secretion by contracting and causing the ejection of preformed saliva.

Ductal System of Salivary Glands

• The ductal system comprises a network of small ducts that unite to form larger ducts, including intercalated ducts, striated ducts, and excretory or collecting ducts.
• Intercalated ducts: connect the terminal secretory units to the larger ducts, with cells that modify the composition of saliva by secretory and resorptive processes.
• Striated ducts: lined by tall columnar epithelial cells with prominent striation at the basal ends of the cells, with functions including electrolyte reabsorption and protein secretion.
• Terminal excretory ducts: the ducts through which salivary fluid from the glands is secreted into the oral cavity, with characteristics changing from pseudostratified columnar epithelium to true stratified squamous epithelium.