Overview
Concise notes on salivary gland structure, cell types, ducts, and functions, organized for study.
Types and Functions of Salivary Glands
- Salivary glands are exocrine glands in the oral cavity secreting saliva.
- Saliva provides antibacterial proteins, lubrication, tooth integrity, and digestion aid.
- Major glands: parotid, submandibular, sublingual; produce ~90% of saliva.
- Minor glands: ~600–1000 small aggregates; widely distributed except gingiva and anterior hard palate.
- Minor glands secrete ~10% of saliva; predominantly mucous for lubrication.
Classification by Secretory Cell Type
- Secretory cells: serous and mucous; glands can be serous, mucous, or mixed.
- Parotid: serous; submandibular: mixed, predominantly serous.
- Sublingual: mixed, predominantly mucous; minor glands mainly mucous.
- Von Ebner’s glands are serous among minor salivary glands.
Gland Architecture and Organization
- Secretory end pieces are acini; connect to oral cavity via ductal system.
- Myoepithelial cells assist secretion by contracting around acini and ducts.
- Glands encased by connective tissue capsule; septa divide into lobes and lobules.
- Lobules contain acini, intercalated ducts, and striated ducts (intra-lobular).
- Excretory ducts between lobules are inter-lobular; larger ones are inter-lobar.
Structural Pathway of Salivary Flow
- Lumen of acini → intercalated duct → striated duct → inter-lobular excretory ducts → inter-lobar ducts → main excretory duct → oral cavity.
- Ductal cells line ducts; perform modification of saliva, especially in striated ducts.
- Analogy: bunch of grapes; grapes are acini, stems/branches are ducts.
Summary Table: Gland Types, Secretions, and Locations
| Gland/Structure | Type | Predominant Secretion | Relative Contribution/Number | Location/Notes |
|---|
| Parotid | Major | Serous | Part of ~90% total | Serous-only acini |
| Submandibular | Major | Mixed (predominantly serous) | Part of ~90% total | Mixed acini |
| Sublingual | Major | Mixed (predominantly mucous) | Part of ~90% total | Mixed acini |
| Minor glands | Minor | Predominantly mucous | ~10% saliva; 600–1000 glands | Throughout oral cavity; except gingiva, anterior hard palate |
| Von Ebner’s | Minor | Serous | Subset of minor glands | Serous-only among minor glands |
Acinar Cell Types and Features
- Serous acini: spherical; 8–12 cells around central lumen.
- Serous cell shape: pyramidal; basal nucleus; apical zymogen granules.
- Zymogen granules contain salivary macromolecules/proteins for secretion.
- Intercellular canaliculi extend from lumen between serous cells.
- Junctional complexes: tight junction (zonula occludens), adherens (zonula adherens), desmosome (macula adherens).
Mucous Acini and Serous Demilunes
- Mucous acinar cells: pyramidal; apical mucin granules; flattened basal nucleus.
- Mucous end pieces: tubular; cells surround a central lumen in cross-section.
- Serous demilune: crescent of serous cells capping mucous acini.
- Mucous acini lack canaliculi; demilunes have canaliculi delivering serous secretions.
- H&E does not show mucin granules; cells appear empty on H&E.
- Special stains: periodic acid–Schiff and alcian blue stain mucin/mucus.
Myoepithelial Cells
- Stellate-shaped epithelial cells with smooth muscle-like contractility.
- Located around secretory end pieces and intercalated ducts.
- Function: contract to aid movement of saliva from acini to ducts.
Duct System: Histology and Function
- Intercalated ducts: simple cuboidal epithelium; central nucleus; scant cytoplasm.
- Intercalated ducts are small; often not visible microscopically.
- Striated ducts: columnar cells; central nucleus; eosinophilic cytoplasm.
- Basal folds with many mitochondria create striated basal appearance.
- Striated ducts perform most ionic transport modifying saliva composition.
- Excretory ducts: inter-lobular with pseudostratified columnar epithelium.
- As ducts enlarge near oral cavity, lining transitions to stratified squamous.
Key Terms & Definitions
- Acinus (acini): secretory end piece housing acinar cells.
- Serous cells: protein-secreting acinar cells with zymogen granules.
- Mucous cells: mucin-secreting acinar cells with mucin granules.
- Serous demilune: crescent-shaped serous cap on mucous acinus.
- Intercellular canaliculi: finger-like lumen extensions between serous cells.
- Myoepithelial cells: contractile epithelial cells assisting secretion.
- Intercalated duct: small duct connecting acini to striated ducts.
- Striated duct: duct with basal infoldings and mitochondria for ion transport.
- Excretory ducts: larger ducts carrying saliva to oral cavity.
- Inter-lobular vs inter-lobar: between lobules vs between lobes respectively.
- Septa (inter-lobular/inter-lobar): connective tissue partitions dividing gland.
Action Items / Next Steps
- Review histological identifiers for serous vs mucous acini and ducts.
- Memorize ductal sequence and epithelial transitions along the pathway.
- Practice identifying demilunes and canaliculi in micrographs with special stains.