Salivary Glands Overview

Salivary Glands

• Salivary glands are exocrine glands comprised of tubules that open into the oral cavity
• Classified as compound tubuloacinar merocrine glands
• Can be major (parotid, submandibular, sublingual) or minor (scattered throughout oral mucosa)
• Classified by secretion type: mucous, serous, or mixed
• Not present in gingiva or the dorsal part of the anterior two-thirds of the tongue

Parotid Gland

• Largest salivary gland
• Secretes 25% of total saliva, mainly serous in adults
• Mixed serous secretion in infants and older adults
• Stenson's duct is the main duct
• Has a capsule with fat cells spaces

Submandibular Gland

• Located at the angle of the mandible
• Second largest salivary gland: secretes 60% of total saliva
• Mixed secretion, predominantly serous
• Has a well-formed connective tissue capsule
• Wharton's duct is the main duct

Sublingual Gland

• Located on the anterior floor of the mouth, secretes 5% of total saliva
• Mixed secretion, predominantly mucous
• Poorly encapsulated or non-encapsulated
• Bartholin's duct is the main duct, 8 to 30 smaller ducts open directly into the oral mucosa

Minor Salivary Glands

• Scattered throughout oral mucosa
• Contribute 5 - 10% of total saliva
• Mostly mucous, except for serous glands of von Ebner associated with circumvallate papillae
• Types:
  • Palatoglossal glands: pharyngeal isthmus
  • Palatal glands: hard and soft palate
  • Anterior lingual glands: near ventral surface of the tongue
  • Posterior lingual glands: root of the tongue

Saliva Composition

• Over 99% water
• Small amounts of inorganic and organic compounds including proteins, glycoproteins and enzymes
• Functions:
  • Lubrication: mucin acts as lubricant during mastication, swallowing, and speech
  • Taste: dissolves substances for taste perception

Myoepithelial cells

• Located between acinar and intercalated duct cells
• Contribute to salivary flow by:
  • Supporting acinar parenchyma
  • Accelerating initial saliva outflow
  • Reducing luminal volume
  • Contributing to secretory pressure
  • Overcoming peripheral resistance
• Structure:
  • Dendritic: stellate shape with radiating processes around acini
  • Elongated, Longitudinal: short processes around intercalated ducts
• Contraction triggered by parasympathetic and sympathetic stimulation
• Possess numerous actin microfilaments

Duct System

• Intralobular (within lobule):

  • Intercalated ducts:
    • Smallest and most distal, drain several acini
    • Lined by cuboidal epithelial cells with secretory granules
    • Modify saliva by adding lysozyme and lactoferrin
  • Striated ducts:
    • Longer and more active than intercalated ducts
    • Lined by simple columnar epithelium
    • Involved in active transport due to high mitochondrial content
    • Secrete epidermal growth factor, lysozyme, kallikrein and IgA

• Interlobular (between lobules):

  • Collecting ducts:
    • Transport saliva; function as collecting ducts
    • Lined by columnar epithelium (may be bi-layered)
    • Have a connective tissue adventitia
    • Merge with stratified squamous epithelium of oral mucosa

• Duct System Comparison Across Salivary Glands:*

• Parotid: Long and branching intercalated and striated ducts

• Submandibular: Shorter intercalated ducts and longer, more obvious striated ducts; less numerous than in parotid

• Sublingual: Less developed duct system; striated ducts usually absent

• Minor: Collecting ducts present, intercalated and striated ducts generally absent

Salivary Glycoproteins

• Mixture of salivary glycoproteins ranging from neutral to acidic
• Serous cells in the parotid gland contain neutral glycoproteins

Oncocytes

• Epithelial cells found singly or in small groups within acini and ducts
• Characterized by numerous mitochondria, reducing other organelles
• Appear acidophilic and granular
• Increase in number with age, likely due to degeneration of normal cells

Age Changes

• Decrease in glandular tissue (number of secretory cells)
• Increase in fibrous tissue, fat cells, inflammatory cells, and oncocytes
• Increase in duct volume
• Hyposalivation ("xerostomia")
• Lymphocytic foci infiltration

Key Points

• Salivary glands are classified based on size and secretion type.
• The parotid gland is the largest, secreting mostly serous saliva.
• The submandibular gland is second largest, secreting a mixed serous and mucous saliva.
• The sublingual gland is the smallest, secreting mostly mucous saliva.
• Myoepithelial cells help regulate saliva flow and contribute to secretory pressure.
• The duct system modifies saliva composition.
• Striated ducts are the site of electrolyte resorption and secretion.
• Salivary glycoproteins can vary in their acidity.
• Oncocytes are characterized by an abundance of mitochondria and increase with age.
• Age-related changes in salivary glands can include hyposalivation and increased lymphocytic foci.

This quiz covers the anatomy and functions of salivary glands, including major glands like the parotid, submandibular, and sublingual. Learn about their structure, secretion types, and associated ducts. Perfect for students studying human anatomy and physiology.