Salivary gland structure and function

SALIVARY GLAND STRUCTURE AND FUNCTION

Najran UniversityFaculty of DentistryDr. Mutaz Ali Hassan

Salivary glands are compound, tubuloacinar, merocrine, exocrine glands the ducts of which open into the oral cavity.

Anatomy:

Classification of salivary glands: According to the size:1. Major salivary glands.2. Minor salivary glands. According to the type of secretion:1. Serous secreting.2. Mucous secreting.3. Mixed.

Anatomy:

Major salivary Glands Parotid: largest,

anterior to ear, serous,25% of total saliva.

Submandibular: Intermediate, angle of mandible,60% of total saliva.

Sublingual: Smallest, anterior floor of mouth, 5% of total saliva.

Anatomy:

Minor salivary Glands Labial (lips) – mixed Buccal (cheeks) -

mixed Palatine - mucous Lingual:1. Anterior – mixed2. Middle – serous3. Posterior – mucous.

Physiology:

Saliva secretion is a reflux function result from afferent stimulation of salivary centers (by various stimuli e.g. taste and mastication).

Saliva composition and function:

1. Water (99%): washing and cleaning of tooth surfaces and mucosa, solubilizing of food for tasting and food bolus formation.

2. Mucin: lubricant, formation of salivary pellicle.

3. Minerals: (Ca ++) remineralization of enamel, (bicarbonate ions) buffering.

Saliva composition and function:

4. Antimicrobial: Ig A, lysozyme, lactoferrin.

5. Digestion: Amylase digest carbohydrate.

6. Tissue repair: short bleeding time of oral tissues, epidermal growth factor (wound healing).

Formation and secretion of saliva

Primary saliva: is hypertonic secreted by acini and intercalated ducts.

Modified saliva: is hypotonic due to reabsorption of Na+ and Cl- and secretion of K+ and bicarbonate, by striated ducts.

Amount of saliva secretion

Resting saliva: 0.1-0.3 ml/min. Stimulated saliva: 1-3 ml/min.

The total daily amount: 500-750 ml/day.

Histology:

Glandular secretory tissue:1. Secretory cells (acini and secretory

ducts).2. Excretory ducts (collecting and main

ducts). Myoepithelial cells: ( contractile cells) Supporting connective tissue

stroma:1. Fibroblasts ( produce collagen).2. Fat cells.3. Plasma cells (produce immunoglobulins

Ig A).

Secretory cells:

Salivary Acinus (acini): Functional unit of the salivary gland. A cluster of pyramidal cells (serous or

mucous or both) that secretes into a lumen.

Secretory cells:

Serous cells: Pyramidal cells with

basophilic granular cytoplasm and basally located nuclei.

Produce proteins and glycoproteins.

Secretory cells:

Mucous cells: Elongated

pyramidal cells with pale vacuolated cytoplasm basally located nuclei.

Produce low proteins high in carbohydrates (mucin).

Secretory cells:

Mixed acini: with serous and

mucous cells. Serous demilune.

Secretory cells:

Intercalated duct:

Lined by cuboidal epithelial cells.

Secretion of protein and electrolyte exchange.

Secretory cells: Striated Ducts: Lined by columnar

cells with eosinophilic abundant cytoplasm.

Microvilli in the luminal surface and striation in basal ends.

Reabsorption of Na+ and Cl-

Secretion of K+ and bicarbonate.

Myoepithelial cells

Star-shape cells with long processes.

Found around acini and intercalated ducts.

Contractile cells that squeeze to empty acini.

Salivary Ductal System

Duct system consists of:1. Secretory portion (intercalated and

striated ducts) which lies within lobules (intralobular)

2. Excretory portion (collecting and main ducts) which lies in the connective tissue septa between lobules (interlobular duct).

Salivary Ductal System

Acinar cells drain directly into intercalated ducts.

Intercalated ducts opens into striated ducts.

Both intercalated and striated are intralobular duct system, which means they are present inside the lobules.

The remaining excretory ducts are interlobular which means it is located within the connective tissue septa.

Excretory ductal portion Collecting ducts: Columnar cells and basal

cells. The basal cells are stem cells

responsible for regeneration. Transport saliva to main

ducts.

Main ducts: Stratified columnar

epithelium, near surface becomes stratified squamous epithelium .

Transport saliva to oral cavity.

Supporting connective tissue stroma:

Surrounds major glands forming CT capsule that extends into body of the gland lobe and lobules called septa.

It carries the blood and nerve supply to the secretory elements.

Nerve supply

Parasympathetic and sympathetic impulses.

Parasympathetic impulses: evoke fluid to be excreted, cause exocytosis, induce contraction of myoepithelial cells (sympathetic too) and cause vasodilatation.

beta-adrenergic receptors that induce protein secretion.

Age changes

Fibrosis and fatty degenerative changes

Presence of oncocytes (eosinophilic cells containing many mitochondria)

Clinical Considerations

Obstruction. Role of drugs. Systemic disorders. Bacterial or viral infections. Therapeutic radiation. Formation of plaque and calculus.

DEVELOPMENT OF THE SALIVARY GLANDS

Salivary gland stages of development:(develop during 6th -7th weeks of intrauterine

life).

Pre-bud stage: thickening of the oral epithelium.

Bud stage: The thickening protrudes into the underlying mesenchyme and invaginates to form a bud.

Pseudoglandular stage: The bud elongates to form solid duct and undergoes branching to produce a cluster of branches and buds.

Canalicular stage: the solid ducts develop lumen.

Terminal bud stage: the solid branches and terminal buds develop lumen and differentiate into various ducts and acini.

The epithelial cells at the center of the cords undergo apoptosis result in lumen formation.

The secretory elements are oral epithelial-derived tissue.

While the surrounding mesenchyme is derived from neural crest.

Epithelial–mesenchymal interactions: branching pattern of the different glands is controlled by signals from the mesenchyme.

Parotid glands begin at 4 to 6 weeks of intrauterine life from ectoderm.

Submandibular glands begin at 6 weeks of intrauterine life from endoderm.

Sublingual & minor glands begins at 8 to 12 weeks of intrauterine life from endoderm.

Intraoral minor salivary glands develop during third month.

Clinical consideration:

Aplasia: congenital absence of one of the major salivary glands.

Atresia: failure of canalization of salivary duct.

Aberrancy: ectopic salivary gland tissue.