EMBRYOLOGICAL DEVELOPMENT OF SALIVARY GLANDS

The formation of major salivary glands is initiated by ectodermal– mesenchymal interaction.
Differentiation of the gut and its derivatives depends on reciprocal interactions between the gut endoderm (epithelium) and its surrounding mesoderm.
HOX genes in the mesoderm are induced by sonic hedgehog (SHH) secreted by gut endoderm.
The major salivary glands start developing from the sixth to the eighth week of gestation as out pouchings of the oral ectoderm into the surrounding mesenchyme.
The first indication is a thickening of the epithelium on the side of the tongue, outside the anlage (anlage, foundation) of the dental arch.
The development of salivary glands consists of five main stages

Pre-bud	Epithelial thickening in the floor of mouth
Bud	Invagination of epithelial thickening into the underlying mesenchyme Formation of a thick solid epithelial stalk terminated by a bulge
Pseudo glandular	Branching morphogenesis: An initial single epithelial bud is turned into an array of epithelial branches that eventually differentiate into a network of ducts, each terminating in a secretory end piece
Canalicular	Hollowing out of branches and buds in their centre by a process of cavitation De novo formation of lumen to create epithelial tubes/future ducts
Terminal differentiation	Maturation of the acini and intercalated ducts Diminishing prominence of interstitial connective tissue

Gland	Time Period	Tissue of Origin
Parotid	6th–8th week of gestation	Ectoderm
Submandibular	6th week	Ectoderm
Sublingual	8th–9th week	Ectoderm
Capsule of all major salivary glands	3rd month	Mesenchyme
Minor salivary glands	12th week IUL	Endoderm