SALIVARY GLAND

Salivary gland

Salivary glands are compound , tubulacinar , merocrine and exocrine gland

Compound: means it has more than one tubule entering the main duct.Tubulacinar: means the morphology of the secreting cellMerocrine: means that only the secretion of the cell is released Excorine: means gland secretes fluid onto a free surface

Saliva*Is a complex fluid , produced by salivary

gland, the most important function is to maintain the well-being of the mouth.

*In human, three pairs of major SG are located outside the O.C with extended duct which open into the mouth, and numerous minor SG which located in the submucosal layer with short ducts that open directly onto mucosal .surface

Composition of Saliva

It contains over than 99% of water, inorganic and organic compounds ( prtn, glycoprtn, enzymes).Mucin= acts as lubricant during masticationLysozyme= antibacterial substanceEpidermal growth factor= produced by submandibular gland involved in wound healing Amylase = digest food.

Compostion of saliva - Kalikernin : enezyme capable of cleaving

peptide bond in prtn (blood coagulation). - Histatin: prevents fungal infection.- Lipase: initiate digestion of fat.- Lactoperoxidase: stimulation of activity of

minor salivary gland.- Mucin: lubricant and preserve mucosal

integrity. - Proline rich prtn: present in enamel pelllicl.- Cystatin: prevent crytal growth of Ca and

phosphat.

Composition of SalivaPARAMETER CHARACTERISTICSVolume: 600-1000 mL/day

-Electrolytes: Na+, K+, Cl–, HCO3−, Ca2+, Mg2+, HSCN–, and FPeptides : Amylase, proline-rich prtn, mucins, histatin, cystatin , Secretory proteins/

lysozyme, lactoferrin,defensins andcathelicidin-LL37

Immunoglobulins: Secretory immunoglobulin A;Small organic: Glucose, amino acids, urea, uric acid, and lipid molecules

adenosine monophosphate-binding Other components: Epidermal growth,

proteins, and serum albumin

FLOW RATE(ML/MIN )WHOLE PAROTID

SUBMANDIBULARResting 0.2-0.4 0.04 0.1Stimulated 2.0-5.0 1.0-2.0 0.8pH 6.7-7.4 6.0-7.8,

The average person produces approximately 0.5 L – 1.5 L per day

• Salivary flow peaks in the afternoon

• Salivary flow decreases at night.

• There is a difference in the quality between stimulated and unstimulated saliva

* Parotid secret a watery saliva rich in enzymes such as amylase, prtn such as proline-rich prtn ,and glycoprtn.

* Submandibular in addition to the above it contains highly glycosylated substance Mucin.

*Sublingual produce a viscous saliva rich in mucin.

*Oral fluid includes the secretion of MSG, MiSG, desqumated epith., MO, food debris and serum and inflammatory cells.

Effect Active Constituent

Protection Lubrication, lavage, pellicle formation

GlycoproteinWater

Buffering Action Regulates pH Phosphate and Bicarbonate

Digestion Digests starchDigests lipidsBolus formation

AmylaseLingual Lipase

Facilitation of Taste Taste bud growth and maturation, dissolves substances to carry to taste buds

Gustin

Defensive Action Against Microbes

AntibodiesHostile Environment

LysozymeLactoferrinIgA

Ionic Exchange Between Tooth Surface

Posteruptive Maturation of EnamelRepair

CalciumPhosphate

Functions of SalivaFUNCTION EFFECT ACTIVE CONSTITUENTSProtection Clearance Water

Lubrication Mucins, glycoproteins

Thermal/chemical insulation Mucins pellicle formation Proteins,

glycoproteins, mucins Tannin binding basic proline-rich proteins,

histatins Buffering pH maintenance Bicarbonate, phosphate, basic proteins, urea, ammonia

Neutralization of acidsTooth integrity Enamel maturation, repair Ca, PO4, F, statherin, acidic proline-rich proteins Antimicrobialactivity

physical barrier Mucins Immune defense Secretory

immunoglobulin A Nonimmune defense Peroxidase, lysozyme,

lactoferrin, histatin, mucins, agglutinins, secretory leukocyte protease inhibitor, defensins and

cathelicidin-LL37 Tissue repair Wound healing, epithelial regeneration Growth factors, trefoil prtnDigestion Bolus formation Water, mucins

Starch,triglyceride digestion Amylase, lipase Taste Solution of molecules Water and lipocalins

Maintenance of taste buds Epidermal growth factor and carbonic anhydrase VIf

Anatomy of salivary glands

-It is the largest gland -Superficial portion lies

subcutanously infront of ear

-Deep portion behind the ramus of mandible

-wt = 14-28 g -Contains facial nerve

-Stensons duct which open infront of 2nd molar

-Supplied from ECA

PAROTID

Submandibular

-Post part of floor of mouth

-Wt = 10-15 g -warton’s duct which

opens beneath the tongue

-Supplied from facial and lingual artries

Sublingual

-Wt = 2 g -Ant part of floor of

mouth -Ducts fo rivinis

which opens into Bartholin duct

-Blood supply from submental and sublingual artries

Minor Salivary Gland

Minor salivary glands are found throughout the mouth: – Lips– Buccal mucosa (cheeks)– Alveolar mucosa (palate)– Tongue dorsum and ventrum – Floor of the mouth

Together, they play a large role in salivary production.

Not present in gingivae and dorsum of anterior 2/3 of the tongue

EmbryologyPRIMORDIA TIME OF

DEVELOPMENT

EMBRYONIC ORIGIN

REGION

Parotid gland primordia

(anlage)

5th to 6th week

Ectoderm Labiogingival sulcus

Submandibular gland

primordia

6th week Endoderm Hyoid arch

Sublingual gland

primordia

7th to 8th week

Endoderm Linguogingival sulcus

Intraoral minor

salivary glands

3rd month

Stages of development STAGE 1 ;- FORMATION INDUCTION OF ORAL EPITHELIUM BY UNDERLYING MESENCHYME.

STAGE 2 ;- FORMATION &GROWTH OF THE EPITHELIAL CORD.

Stages of development STAGE 3. INITIATION OF BRANCHING IN TERMINAL PARTS OF THE EPITHELIAL CORD

&CONTINUATION OF GLANDULAR DIFFERENTIATION.

STAGE 4. REPETITIVE BRANCHING OF THE EPITHELIAL CORD &LOBULE FORMATION

Stages of development

STAGE 5 ;-CANALIZATION OF PRESUMPTIVE DUCTS

STAGE 6. ;- CYTODIFFERENTIATION

STRUCTURE OF SALIVARY GALND

*Each salivary glands Consist of two main elements :

-Glandular secretory tissue ( parenchyma)

-Supporting connective tissue ( stroma)

-from the stroma of capsule pass septa that divide the gland into major lobes which further divide into lobules

The Secretory Units - ACINI

*A grape-like cluster of parenchymal cells around a lumen

*Types - Serous - Mucous

- Mixed (Serous Demilunes capping mucous cells)

*Myoepithelial cells around the acini - Contractile cells with several processes

- Synonyms: basket cells

The Duct System

*Intra-lobular - Acinus Lumen

- Intercalated ducts - Striated Duct

*In intra-lobular system, - Plazma cells in stroma

- Electrolytes - Epidermal GF (produced and secreted by the

submandibular salivary gland) 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 - Capsular

- Inter-Lobar - Inter-Lobular - Inter-acinous

*Capsular, inter-lobar and inter-lobular septa contain blood vessels and nerves

*Constituents - Collagen Fibers

- Fibroblasts - Fat Cells

* With age there is decrease in parenchyma and an increase in stroma (esp. fat cells)

Parenchyma• Epithelial cells

containing secretory granules

Stroma

Duct

Can be distinguished by the nature of their secretion, the structural term and the morphology of secretory granules

SEROUS MUCOUS

* The acinus via its lumen empties into and intercalated duct lined with cuboidal epithelium , which in turn joins a larger striated duct formed of columnar cells

-Both are intralobular and affect the secretion of passing through them

-Plasma cells ( which secrete the IG) are found in the stroma of the gland around the intralobular ducts.

-Striated duct empty into inert collecting duct which carry the saliva to mucosal surface and may be lined near their termination by a layer of stratified squamous epithelial cell.

-The collecting duct are interlobular.

-The connective tissue septa carry the blood and nerve into parenchym.

Ductal System

Intralobular

ExcretoryStriated

Intercalated

Interlobular

Serous cells

Pear-shaped groups of epithelial cells with distinct basement membraneDense cytoplasmRound, central nucleusZymogen granules are presentMyoepithelial cells between epithelium and basement membrane of acini

-Spherical shaped consist of 8-12 cells

-Base to connective tisse and apex to lumen

-Nucleus in the basal part -Secretory granules which is rich in

macromolecules in apical cytoplasm.

-Basa, l cytoplasm contains RER, golgi complex, mitochondria lysosomes

-Plasma membrane contains intercellular canalliuli w short microvilli.

-Lateral surface has interdigitated folds to increase surface area.

--it is joined by tight junction , adhereing junciton and desomsomes

Mucus cells

Larger than serous aciniAbundant cytoplasm filled with clear mucusPyramidal cells with flattened basal nucleiMyoepithelial cells between epithelium and basement membrane of aciniPresence of mucigen granules

Tubular configurationCentral lumen larger than serous Has serous demilune covering its ends

-Apical cytoplasm contains mucin which compress and flatten the nuclues

-Large golgi complex basal to secretory granules

- -lack of intercellular canalliculi except in the demilune end

Serous acinusThin watery secretionZymogen granules

Nucleus: Round, centralLumen: SmallDarkly stainedEnzyme actionIndistinct cell boundaries

Eg: Parotid gland

Thick viscous secretionMucigen granulesFlat, peripheralLumen: largeLightly stainedProtection and lubricationDistinct cell boundariesEg: Sublingual gland

Mucus acinus

Myoepithelial Cells

MYOEPITHELIAL CELLS:Flat, indistinct cells with long cytoplasmic processes that aid in contractionLie between epithelial cells and basal lamina of the acini where they are well-developed and branchedCalled “basket cells” around the aciniME also found around intercalated ducts but are more spindled

Myoepithilial -Contractile cells around

serous and intercalated duct.

-From epithilial origin located between basal lamina and duct cells which linked to them by desosomes.

-Around the secretory end it is stellate shape

-Its organlles located perinuclear in cytoplasm

-Around intercalated duct it is fusiform shape.

-Contraction around secretory portion help to support the acini during active secretion

-Also help into emptying the content

-Around intercalated duct it wide and shorted the duct help to maintain its patency.

Myoepithileal cell -it contains

cytokeratin intermediate filament and contractile actin filaments, which can be used to help identify them using

Immunocytochemistry

-

Ductal System

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Secretions pass through a system of ducts

Smallest – intercalated ducts lined by flattened cells

Intercalated ducts open into striated ducts lined by cuboidal cells

Striated ducts open into excretory ducts lined by simple columnar epithelium

Intercalated ducts

Classified as intralobular duct

Cuboidal epithelial cells

Smallest branch of the system of ducts

Prominent in Salivary Glands

Intercalated duct

Centrally placed nuclei and small amount of cytoplasm containing EPR, and a small glogi complex.

A few small secretory granules may be found in apical cytoplasm.

In parotid, they are long, narrow, and branching

Striated duct Formed by union of

intercalated duct

Columnar cell with centrally placed nucleus and pale acidophillic cytoplasm.

Basal lamnia encloses it and capillary plexus is present.

Striated duct cell Numerous elongated mitochondria in narrow cytoplasmic partitions separated by highly folded and interdigitated basolaterla cell membrane.Apical cytoplasm contain secretry granules which contain kallikreinIt also contains numerous lysosomes and peroxisomes and deposits of glycogen.Adjacent cells are joined by well developed tight junction but lack gap juction

Terminal Excretory duct

they locate in the connective tissue septa btwn the lobules of the gland .

They are larger in diameter than striated duct and typically have pseudostratified epithelium with columnar cells

Terminal Excretory Cell

as the duct increase in size the number of mitochondria and the extent of infolding of basolateral membrane decrease

Parotid Gland

Purely serous

Intercalated cells are numerous and long in it

Striated duct are numerous and

appear acidophillic.

Submandibular

Mixed, 90% serous 10% mucous

The intercalated and striated ducts are less numerous than those in parotidSecretes lysozymes

1 :intralobular ducts/ striated ducts

2 :mucous acinus3 :serous demilunes

Sublingual gland

Mixed gland, but mucous secretory cells predominate.The intercalated duct are short and difficult to recognize.Intralobular ducts are fewer in number and some duct lack the infolded basolateral membrane of striated duct

Minor Salivary Gland -the secretory end

pieces of most minor glands are mucous or have a small serous component.

-intercalated duct often poorly developed and the larger duct may lack infolded basolateral membrane of striated duct.

-Von Ebner gland is purely serous , located below the circumvallate papillae

Clinical consideration

AGING : -Generalized loss of SG parenchymal tissue, a

gradual reduction of up to 30% to 60% in the proportional acinar volume.

-The lost salivary cell is replaced by adipose cell. -An increase In fibrous connective tissue and

vascular elements. -Changes of the duct system including an

increase in nonstriated intralobular ducts, dilation of extralobular duct and degenerative and metplastic occure.

AGE CHANGE

-Although decreased production of saliva often is observed in older persons wether this is related directly to the reduction in parenchymal tissue is not clear yet.

-Some studies of healthy older individuals in which the use of medication were controlled carefully revealed little or no loss of salivary function.

-Other studies suggest that although resting salivary secretion is in the normal range the volume of saliva produced during stimulated secretion is less than normal

Sialoliths

Sialoliths are common in the submandibular gland duct,

because..……Anatomical course of wharton’s duct has sharp curves which may trap mucin/calculusHigh mucin level of the gland may trap foreign bodies &debris Calcium content is higher in the saliva of sub.mand. GlandFlow rate of the saliva is slower than parotidDependent position of the gland increases chances of stasis of saliva

sialolith

Clinical features: Intermittent swelling in the region of major salivary gland that enlarges during eating and resolves later Pain because of the back up saliva behind the stone

Sialolith

Stasis of saliva may lead to infection /fibrosis /atropy of the glandSinus /fistula and ulceration in chronic casesThey may be palpable if they are at periphery of the ductThey are circumscribed &firm to hard masses

Sialolith

Etiology /p. factors [Debatable]InflammationDrugs [anticholenergic medications,antihistamines]Defects in calcium and phospharous metabolism

-Ttt could be by surgery or antibiotic

Dry mouth (xerostomia)

-Clinical compliant. -Loss of salivary function or a reduction in the volume

of secreted saliva may feel to the sensation of oral dryness.

-Most commonly as a side effect of medications taken by the patient which cause central or peripheral inhibition of salivary secretion.

-Destruction of salivary gland tissue another cause.-Loss of gland function occurs after radiation therapy

for head and neck cancer. -Chemotherapy for cancer or associated with bone

marrow transplantation also reduce salivary function

Xerostomia

-Autoimmune disease in particular sjogren syndrom.

-The decreased volume of saliva leads to drying of oral tissue.Loss of the protective effect of salivary buffers prtn and mucin-

Xerostomia

-The oral tissues are more susceptible to infections

-Speech, swallowing and eating become very difficult and painfull

-Teeth are highly susceptible to caries especially near the gingival margin

Xerostomia

-Temporary relief is achieved by frequent sipping of water or artificial saliva.

-Patient who have some functional salivary tissue may benefit from pharmacologic therapy with oral parasympathomimetic drugs such as pilocarpine to increase salivary flow.

-Satisfactory ttt may include genetic modification of salivary gland cells to increase fluid and protein secretion