Transcript Salivary Glands - student.ahc.umn.edu

Salivary Glands
Major glands
• Parotid: so-called watery serous saliva rich
in amylase, proline-rich proteins
– Stenson’s duct
• Submandibular gland: more mucinous
– Wharton’s duct
• Sublingual: viscous saliva
– ducts of Rivinus; duct of Bartholin
Minor glands
• Minor salivary glands are not found within
gingiva and anterior part of the hard palate
• Serous minor glands=von Ebner below the sulci of
the circumvallate and folliate papillae of the
tongue
• Glands of Blandin-Nuhn: ventral tongue
• Palatine, glossopalatine glands are pure mucus
• Weber glands
Functions
• Protection
– lubricant (glycoprotein)
– barrier against noxious stimuli; microbial toxins
and minor traumas
– washing non-adherent and acellular debris
– formation of salivary pellicle
• calcium-binding proteins: tooth protection; plaque
Functions
• Buffering (phosphate ions and bicarbonate)
– bacteria require specific pH conditions
– plaque microorganisms produce acids from
sugars
Functions
• Digestion
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neutralizes esophageal contents
dilutes gastric chyme
forms food bolus
brakes starch
Functions
• Antimicrobial
– lysozyme hydrolyzes cell walls of some
bacteria
– lactoferrin binds free iron and deprives bacteria
of this essential element
– IgA agglutinates microorganisms
Functions
• Maintenance of tooth integrity
– calcium and phosphate ions
• ionic exchange with tooth surface
Functions
• Tissue repair
– bleeding time of oral tissues shorter than other
tissues
– resulting clot less solid than normal
– remineralization
Functions
• Taste
– solubilizing of food substances that can be
sensed by receptors
– trophic effect on receptors
Embryonic development
• The parotid: ectoderm (4-6 weeks of embryonic
life)
• The sublingual-submandibular glands: endoderm
• The submandibular gland around the 6th week
• The sublingual and the minor glands develop
around the 8-12 week
• Differentiation of the ectomesenchyme
• Development of fibrous capsule
• Formation of septa that divide the gland into lobes
and lobules
Serous cells
• Seromucus cells=secrete also polysaccharides
• They have all the features of a cell specialized for
the synthesis, storage, and secretion of protein
– Rough endoplasmic reticulum (ribosomal sites->cisternae)
– Prominent Golgi-->carbohydrate moieties are added
Secretory granules-->exocytosis
Serous cells
• The secretory process is continuous but cyclic
• There are complex foldings of cytoplasmic
membrane
• The junctional complex consists of:
– Tight junctions (zonula occludens)-->fusion of outer cell
layer
– Intermediate junction (zonula adherens)-->intercellular
communication
– Desmosomes-->firm adhesion
Mucous cells
• Production, storage, and secretion of
proteinaceous material; smaller enzymatic
component
-more carbohydrates-->mucins=more
prominent Golgi
-less prominent (conspicuous) rough
endoplasmic reticulum, mitochondria
-less interdigitations
Formation and Secretion of Saliva
• Primary saliva
– Serous and mucous cells
– Intercalated ducts
• Modified saliva
– Striated and terminal ducts
– End product is hypotonic
Macromolecular component
• Synthesis of proteins
• RER, Golgi apparatus
• Ribosomes  RER  posttranslational
modification (N- & O-linked glycosylation)
 Golgi apparatus  Secretory granules
• Exocytosis
• Endocytosis of the granule membrane
Fluid and Electrolytes
• Parasympathetic innervation
• Binding of acetylcholine to muscarinic
receptors
– Activation of phospholipase  IP3  release of
Ca2+  opening of channels K+, Cl- Na+ in
– K+ and Cl- in
– Also another electrolyte transport mechanism
through HCO3-
• Noepinephrine via alpha-adrenergic receptors
– Substance P activates the Ca2+
Myoepithelial cells
• One, two or even three myoepithelial cells
in each salivary and piece body
• Four to eight processes
• Desmosomes between myoepithelial cells
and secretory cells
• Myofilaments frequently aggregated to
form dark bodies along the course of the
process
Myoepithelial cells
• The myoepithelial cells of the intercalated ducts
are more spindled-shaped and fewer processes
• Ultrastructurally very similar to that of smooth
muscle cells
• Functions of myoepithelial cells
– Support secretory cells
– Contract and widen the diameter of the intercalated
ducts
– Contraction may aid in the rupture of acinar cells of
epithelial origin
Intercalated Ducts
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Small diameter
Lined by small cuboidal cells
Nucleus located in the center
Well-developed RER, Golgi apparatus,
occasionally secretory granules, few microvilli
• Myoepithelial cells are also present
• Intercalated ducts are prominent in salivary glands
having a watery secretion (parotid).
Striated Ducts
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Columnar cells
Centrally located nucleus
Eosinophilic cytoplasm
Prominenty striations
– Indentations of the cytoplasmic membrane with many
mitochondria present between the folds
• Some RER and some Golgi, short microvilli
• Modify the secretion
– Hypotonic solution=low sodium and chloride and
high potassium
• Basal cells
Terminal excretory ducts
• Near the striated ducts they have the same
histology as the striated ducts
• As the duct reaches the oral mucosa the
lining becomes stratified
• Goblet cells, basal cells, clear cells.
• Alter the electrolyte concentration and add
mucoid substance.
Ductal modification
• Autonomic nervous system
• Striated and terminal ducts
• Modofication via reabsorption and secretion of
electrolytes
• Final product is hypotonic
• Rate of salivary flow
– High: Sodium and chlorine up; potassium down
Connective tissue
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Fibroblasts
Inflammatory cells
Mast cells
Adipose cells
Extracellular matrix
– Glycoproteins and proteoglycans
• Collagen and oxytalan fibers
• Blood supply
Nerve supply
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No direct inhibitory innervation
Parasympathetic and sympathetic impulses
Parasympathetic are more prevalent.
Parasympathetic impulses may occur in
isolation, evoke most of the fluid to be
excreted, cause exocytosis, induce
contraction of myoepithelial cells
(sympathetic too) and cause vasodilatation.
Nerve supply
• There are two types of innervation:
Epilemmal and hypolemmal
• beta-adrenergic receptors that induce
protein secretion
• L-adrenergic and cholinergic receptors that
induce water and electrolyte secretion
Hormones can influence the function of the
salivary glands. They modify the salivary
content but cannot iniate salivary flow.
Age changes
• Fibrosis and fatty degenerative changes
• Presence of oncocytes (eosinophilic cells
containing many mitochondria)
Clinical Considerations
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Obstruction
Role of drugs
Systemic disorders
Bacterial or viral infections
Therapeutic radiation
Formation of plaque and calculus