Salivary Glands

SALIVARY GLANDS Oral Histology Dent 205 Summer semester 2005/2006

Salivary Glands 

Characteristics    

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Compound – more than one tubule entering the main duct Tubuloacinar – morphology of secreting cells Merocrine – only secretion of the cell is released Exocrine – secretion onto a free surface

Physiology     

Stimulants-taste and mastication Autonomic nervous system – Afferent nerves Salivary centre Autonomic nervous system – Efferent nerves Secretion

Classification of Salivary Glands 

Size 

Major   

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Minor: scattered throughout the oral mucosa 

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Parotid Submandibular Sublingual

Labial, buccal, palatoglossal, palatal, and lingual mucosae Not present in gingivae and dorsum of anterior 2/3 of the tongue

Secretion   

Mucous Serous Mixed

Saliva 

Constituents  

Water-99% Organic Proteins  Glycoproteins  Enzymes 

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Inorganic 

Minerals

Saliva 

Functions 

Lubrication  

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Taste Antibacterial and immunity  

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Minerals Helps in maintaining the integrity of enamel

Wound healing and upper GI mucosal integrity 

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Amylase

Buffering 

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Lysozyme IgA – produced by plasma cells

Digestion 

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Mucin Physical protection of oral mucosa

Epidermal Growth Factor – produced and secreted by the submandibular salivary glands

Blood coagulation 

Kallikrein

Salivary Glands 

Main tissue elements 

Glandular secretory tissue   

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Supporting Connective tissue  

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Parenchyma Ectodermal Acini and duct epithelium Stroma Mesodermal

Macro-to-microscopic levels    

Gland Lobe Lobule Secretory units – Acini

The Secretory Units - ACINI 

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A grape-like cluster of parenchymal cells around a lumen Types   

Serous Mucous Mixed 

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Serous demilunes capping mucous cells

Myoepithelial cells around the acini 

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Contactile cells with several processes Synonyms: basket cells

The Duct System 

Intra-lobular Acinus lumen  Intercalated ducts  Striated duct * In intra-lobular system, composition is affected 

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Plasma cells in stroma Electrolytes Epidermal GF and Kallikrein

Inter-lobular Collecting ducts *The inter-lobular system is inert, does not affect the composition 

Stroma   

Connective tissue Mesenchymal origin Macro-to-microscopic levels    

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Capsular Inter-lobar Inter-lobular Inter-acinous

Capsular, inter-lobar, and interlobular septa contain blood vessels and nerves Constituents   

Collagen fibers Fibroblasts Fat cells 

With age, there is a decrease in parenchyma and an increase in stroma (esp. far cells)

Synthesis of Saliva   

Active secretory process Not a blood ultra-filtrate Serous cells 

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Mucous cells 

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Watery proteinaceous fluid contains amylase Proteins linked to a greater amount of carbohyrates

Plasma cells 

IgA

Secretion of Saliva 

Throughout the day  

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Average flow rate (90% from Major SG)  

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Low level in general Periodic large addition from major glands 0.3 ml/min 500-700 ml/day

Contribution of gingival fluids Secretion 

Spontaneous 

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Stimulated (nerve-mediated)  

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Small amounts from sublingual and minor SGs The bulk of saliva from all glands Parotid and Submandibular SGs do not secret spontaneously

Anaesthesia ceases secretion as it is nerve-mediated

Serous cells 

Light Microscopy 

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Basophilic because of Rough Endoplasmic Reticulum Characteristic granular appearance with H & E Round prominent nuclei located at the basal third of the cell

Ultra-structure   

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Wedge-shaped outline Basal lamina separates from stroma Luminal part contains zymogen granules Microvilli Desmosomes, gap and tight junctions

Mucous cells   

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Appear pale in H & E stains Basally-compressed nuclei Acini may be surrounded by crescent-shaped serous demilunes Debate whether demilunes are connected with the lumen Mucin granules

Acinus lumen

Serous demilunes

Mucous cells

Myoepithelial cells 

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Lie between basal lamina and basal membranes of acinar cells and ICD Around acinar cells  

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Around ICD  

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Longitudinal Few short processes

Contracttion  

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Dendritic Long tapering processes

Parasympathetic Sympathetic

Ultra-structure   

Flattened nucleus Desmosomes with parenchymal cells Gap junctions and hemidesmosomes with basal lamina

Intercalated ducts     

Drainage from several acini Compressed between the acini Cuboidal epithelial cells Prominent nuclei In Parotid, they are long, narrow, and branching

Striated ducts     

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Larger and longer than ICD Simple columnar epithelium Cells have large centrally-located nuclei Luminal surfaces have microvilli Basal surfaces separated from connective tissue by basal lamina Striation (in light microscopy) corresponds to multiple infoldings of the basal membrane of the cells Desmosomes Electrolyte re-absorption (active) and secretion Secretion of Epidermal GF and Kallikrein

Collecting ducts 

Bi-layered epithelium (lacks striation)  

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Columnar epithelial layer Basal layer

As it enlarges, it gets a connective tissue adventitia Terminated as stratified epithelium to merge with the oral mucosa

Parotid gland    

The largest Serous Acini Adult PG vs. Infant’s PG Fat cells vs. age

Submandibular gland  

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2nd largest Mixed serousmucous secretion (7:3) Intercalated ducts are short and difficult to locate Striated ducts are long and obvious

Sublingual glands 

2 segments all empty to the sublingual fold  

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Major sublingual gland 8 - 30 mixed minor SGs

Mixed gland, mucous outnumber serous cells Most of the serous cells are in demilunes Lacking striated ducts

Minor Salivary glands  

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Primarily mucous Labial, buccal, palatal, palatoglossal, and lingual Lingual glands 

Anterior glands 

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Posterior glands  

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Embedded in muscle near the ventral surface of the tongue Mucous glands At the root of the tongue Mucous glands

Von Ebner glands  

Serous Associated with the Circumvallate papillae

Clinical Considerations 

Dry Mouth (xerostomia) 

Causes  

Ageing – Parenchymal tissue < Stroma Drugs  

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Central action on the salivary centre Diuretics, sedatives, hypnotics, antihistamines, antihypertensives, antipsychotics, antidepressants, anticholinergics, and appetite suppressants

Loss / destruction of salivary tissue  

Radiotherapy Autoimmune disorders 

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Sjogren’s syndrome – destruction by lymphoid tissue (autoimmune disease)

Salivary gland surgery

Endocrine disorders  

Diabetes Hyperthyroidism

Clinical Considerations 

Dry mouth (xerostomia) 

Signs and symptoms    

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Dry, red, glossy atrophic mucosa Difficulty chewing, swallowing, or speaking Altered / diminished taste ability Dental caries  Saliva contains re-mineralising minerals Periodontal disease Candidal infection

Treatment    

Consider stopping offending medication Commercial saliva substitute Fluoride Supplementation Scrupulous dental care

Clinical considerations 

Obstructive disorders 

Sialolithiasis (salivary calculi) 

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Mucoceles and cysts  

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Submandibular and sublingual SGs

Viral 

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Mumps

Bacterial – uncommon 

Suppurative parotitis

Autoimmune diseases 

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Inflammatory disorders (Sialadenitis) 

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Minor SGs Retention of mucous outside the duct

Ranula 

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80% in submandibular SG

Sjogren’s syndrome

Salivary gland tumours

http://www.infocompu.com/adolfo_arthur/images/ranula.jpg