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Salivary Glands

Salivary Glands

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Salivary Glands

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  1. Salivary Glands

  2. 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

  3. 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

  4. 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

  5. Functions • Buffering (phosphate ions and bicarbonate) • bacteria require specific pH conditions • plaque microorganisms produce acids from sugars

  6. Functions • Digestion • neutralizes esophageal contents • dilutes gastric chyme • forms food bolus • brakes starch

  7. Functions • Antimicrobial • lysozyme hydrolyzes cell walls of some bacteria • lactoferrin binds free iron and deprives bacteria of this essential element • IgA agglutinates microorganisms

  8. Functions • Maintenance of tooth integrity • calcium and phosphate ions • ionic exchange with tooth surface

  9. Functions • Tissue repair • bleeding time of oral tissues shorter than other tissues • resulting clot less solid than normal • remineralization

  10. Functions • Taste • solubilizing of food substances that can be sensed by receptors • trophic effect on receptors

  11. 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

  12. 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 addedSecretory granules-->exocytosis

  13. 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

  14. 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

  15. Formation and Secretion of Saliva • Primary saliva • Serous and mucous cells • Intercalated ducts • Modified saliva • Striated and terminal ducts • End product is hypotonic

  16. 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

  17. 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+

  18. 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

  19. 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

  20. Intercalated Ducts • 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).

  21. Striated Ducts • 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

  22. 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.

  23. 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