Salivary Glands and Saliva

Salivary Glands and Saliva

Oral cavityEntrance door of the gastrointestinal tract;Beginning of the digestive function;Provides security of the body against food and drink;Prior to the adoption act two strong evolutionary verified sensory systems:Appearance;Flavor;When they enter in the mouth triggers the umbrella of the immune system:Cell-associated protection:Phagocytes and lymphocytes;Secretory immunity system mainly protects mucous with secretory IgA.Additional protection in the mouthTaste - taste buds;Tactile sense - proprioception ;Saliva.Liquid oral environmentThis is the liquid into the oral cavity, washing mucosa and dental enamel;It consists of:Saliva;Gingival sulcus fluid;Peeling epithelial cells and their degradation products;Microorganisms and their products.

SalivaSaliva is a complex fluid that in health almost continually bathes the parts of the tooth exposed within the oral cavity;Consequently, saliva represents the immediate environment of the tooth.ProductionSaliva is produced by three paired sets of major salivary glands:Parotid;Submandibular;Sublingual glands;and by the many minor salivary glands scatteredthroughout the oral cavity.Account of the compositionA precise account of the composition of saliva is difficult because not only are the secretions of each of the major and minor salivary glands is different, but their volume may vary at any given time. In recognition of this variability, the term mixed saliva has been used to describe the fluid of the oral cavity.Saliva has several functionsSaliva moistens the mouth; Facilitates speech; Lubricates food; Helps with taste by acting as a solvent for food molecules; Saliva also contains a digestive enzyme (amylase); Saliva dilutes noxious material mistakenly taken into the mouth; Cleanses the mouth;Furthermore, it contains antibodies and antimicrobial substances; Its buffering capacity plays an important role in maintaining the pH of the oral cavity.There are three major pairs of salivary glands that differ in the type of secretion they produce:parotid glands - produce a serous, watery secretion.

submaxillary (mandibular) glands - produce a mixed serous and mucous secretion.

sublingual glands - secrete a saliva that is predominantly mucous in character.

Three pairs of major salivary glandsThey are located outside the oral cavity, with extended duct systems through which the gland secretions reach the mouth.Numeroussmaller minor salivary glandsThey are located in various parts of the oral cavitythe labial, lingual, palatal, buccal,glossopalatine,and retromolar glandsThey are typically located in the submucosal layer with short ducts opening directly onto the mucosal surface.

- Minor mucous salivary gland, located in the submucosa below the epithelium of the oral cavity.

Composition of Saliva

PARAMETERVolume Electrolytes

Secretory proteins/Peptides

Immunoglobulins

Small organic

Other componentsCHARACTERISTICS600-1000 mL/day

Na+, K+, Cl, HCO3, Ca2+, Mg2+, HPO42, and F

Amylase, proline-rich proteins, mucins,histatin, cystatin, peroxidase, lysozyme, lactoferrin, defensins, and cathelicidin-LL37

Secretory immunoglobulin A;immunoglobulins G and M;

Glucose, amino acids, urea, uric acid, and lipid molecule

Epidermal growth factor, insulin, cyclic adenosine monophosphatebinding proteins, and serum albuminFLOW RATE(ML/MIN)WHOLEPAROTIDSUBMANDIBULARResting0.2-0.4 0.04 0.1Stimulated2.0-5.01.0-2.00.8pH6.7-7.46.0-7.8The basic secretory units of salivary glands are clusters ofcellscalled an acini;These cells secrete a fluid that contains water, electrolytes, mucus and enzymes, all of which flow out of the acinus into collecting ducts.

Acinar epithelial cellsTwo basic types of acinar epithelial cells exist:serous cells, which secrete a watery fluid, essentially devoid of mucus.mucous cells, which produce a very mucus-rich secretion.Small collecting ducts within salivary glands lead into larger ducts, eventually forming a single large duct that empties into the oral cavity.

Superficialtemporal vesselsTransverse facial arteryParotid ductBranches of facial nerveFacial arterySubmandibular glandMasseter muscleAnterior facial veinSternocleidomastoid muscleGreatauricularnerveParotidglandThe parotid gland is the largest salivary gland.The superficial portion of the parotid gland is located subcutaneously, in front of the external ear, and its deeper portion lies behind the ramus of the mandible.The parotid gland is associated intimately with peripheral branches of the facial nerve;The parotid gland receives its blood supply from branches of the external carotid artery as they pass through the gland.

The duct (Stensens duct) of the parotid gland runs forward across the masseter muscle, turns inward at the anterior border of the masseter, and opens into the oral cavity at a papilla opposite the maxillary second molar.

TongueSublingual ductsSubmandibular ductSublingual glandSubmandibular glandThe major glands are bilaterally paired and have long ducts that convey their saliva to the oral cavity.Submandibular glandThe submandibular gland is situated in the posterior part of the floor of the mouth, adjacent to the medial aspect of the mandible and wrapping around the posterior border of the mylohyoid muscle;The excretory duct (Whartons duct) of the submandibular gland runs forward above the mylohyoid muscle and opens into the mouth beneath the tongue at the sublingual caruncle, lateral to the lingual frenum.The submandibular gland receives its blood supply from the facial and lingual arteries. The parasympathetic nerve supply is derived mainly from the facial nerve, reaching the gland through the lingual nerve and submandibular ganglion.

Submandibular glandSublingual glandThe sublingual gland is the smallest of the paired major salivary glands;The gland is located in the anterior part of the floor of the mouth between the mucosa and the mylohyoid muscle; The secretions of the sublingual gland enter the oral cavity through a series of small ducts (ducts of Rivinus) opening along the sublingual fold and often through a larger duct (Bartholins duct) that opens with the submandibular duct at the sublingual caruncle. The sublingual gland receives its blood supply from the sublingual and submental arteries. The facial nerve provides the parasympathetic innervation of the sublingual gland, also via the lingual nerve and submandibular duct at the sublingual caruncle

Sublingual glandThe minor salivary glandsThey are estimated to number between 600 and 1000, exist as small, discrete aggregates of secretory tissue present in the submucosa throughout most of the oral cavity. The only places they are not found are the gingiva and the anterior part of the hard palate.They are predominantly mucous glands, except for the lingual serous glands (Ebners glands) that are located in the tongue and open into the troughs surrounding the circumvallate papillae on the dorsum of the tongue and at the foliate papillae on the sides of the tongue.

Salivary gland showing its lobular organization.Thicker partitions of connective tissue (septa), continuous with the capsule and within which run the nerves and blood vessels supplying the gland, invest the excretory ducts and divide the gland into lobes and lobules.

LobuleConnectivetissueseptumA salivary gland may be likened to a bunch of grapes.Each grape is the acinus or terminal secretory unit, which is a mass of secretory cells surrounding a central space;The spaces of the acini open into ducts running through the gland that are called successively the intercalated, striated, and excretory ducts analogous to the stalks and stems of a bunch of grapes.These ducts are more than passive conduits, however their lining cells have a function in determining the final composition of saliva.The ducts and acini constitute the parenchyma of the stroma carrying blood vessels and nerves. This connective tissue supports each individual acinus and divides the gland into a series of lobes o lobules, finally encapsulating it.Diagrammatic illustration of the ductal system of a salivary gland.

The main excretory duct, which empties into the oral cavity, divides into progressively smaller interlobar and interlobular excretory ducts that enter the lobes and lobules of the gland.The predominant intralobular ductal component is the striated duct, which plays a major role in modification of the primary saliva produced by the secretory end pieces.Connecting the striated ducts to the secretory end pieces are intercalated ducts, which branch once or twice before joining individual end pieces.The lumen of the end piece is continuous with that of the intercalated duct.

Mainexcretory ductExcretory ductStriated ductIntercalated ductCanaliculusbetween cellsTubular secretoryend piece

Spherical secretory and pieceIntercellular canaliculiIn some glands, small extensions of the lumen, intercellular canaliculi, are found between adjacent secretory cells; These intercellular canaliculi may extend almost to the base of the secretory cells and serve to increase the size of the secretory (luminal) surface of the cells.

LuNAcini - the basic histologic structure of the major salivary glands is similar Acini in the parotid glands are almost exclusively of the serous type, while those in the sublingual glands are predominantly mucous cells. In the submaxillary glands, it is common to observe acini composed of both serous and mucous epithelial cells.

SECRETORY CELLSSerous and mucous cells differ in structure and in the types of macromolecular components that they produce and secrete.

Serous cellsIn general, serous cells produce proteins and glycoproteins (proteins modified by the addition of sugar residues [glycosylation]), many of which have well-defined enzymatic, antimicrobial, calciumbinding, or other activities. Typically, serous glycoproteins have N-linked (bound to the -amide of asparagine) oligosaccharide side chains.

Serous cellSecretory end pieces that are composed of serous cells are typically spherical and consist of 8 to 12 cells surrounding a central lumen;The cells are pyramidal, with a broad base adjacent to the connective tissue stroma and a narrow apex forming part of the lumen of the end piece. The lumen usually has fingerlike extensions located between adjacent cells called intercellular canaliculi that increase the size of the luminal surface of the cells. The spherical nuclei are located basally, and occasionally, binucleated cells are seen.Numerous secretory granules, in which the macromolecular components of saliva are stored, are present in the apical cytoplasm

Intercellular canaliculi are seen inlongitudinal (right) and cross section (left).Mucous cellsThe main products of mucous cells are mucins, which have a protein core (apomucin) that is organized into specific domains and is highly substituted with sugar residues. Mucins are therefore also glycoproteins, but they differ from most serous cell glycoproteins in the structure of the protein core.Mucins function mainly to lubricate and form a barrier on surfaces and to bind and aggregate microorganisms.Mucous cells secrete few, if any, other macromolecular components.

Mucous CellsSecretory end pieces that are composed of mucous cells typically have a tubular configuration;When cut in cross section, these tubules appear as round profiles with mucous cells surrounding a central lumen.

LuThe nuclei (arrowheads) are flattened and compressed against the basal surfaces of the cells

The lumina (Lu) are large compared with those of serous acini.Mucous cell.The most prominent feature of mucous cells is the accumulation in the apical cytoplasm of large amounts of secretory product (mucus), which compresses the nucleus an endoplasmic reticulum against the basal cell membrane.

Distinction between serous cells and mucous cellsIn recent years the distinction between serous cells and mucous cells has become somewhat blurred. Serous cells of some salivary glands are known to produce certain type of mucins, and some mucous cells are thought to produce certain nonglycosylated proteins. Submandibular glandContain mucous cells coated with serous cells called crescent;Serous fluid passes down through the channels between terminal mucinous cells to the lumen of the alveoli.

DuctsWithin the ducts, the composition of the secretion is altered.Much of the sodium is actively reabsorbed, potassium is secreted, and large quantities of bicarbonate ions are secreted.

Striated duct

DUCTSThe ductal system of salivary glands is a varied network of tubules that progressively increase in diameter, beginning at the secretory end pieces and extending to the oral cavity; The three classes of ducts are:intercalated, striated, and excretory, each with differing structure and function. The ductal system is more than just a simple conduit for the passage of saliva; It actively participates in the production and modification of saliva.

Excretory ductstriated,intercalatedIntercalated DuctsThe primary saliva produced by the secretory end pieces passes first through the intercalated ducts;The first cells of the intercalated duct are directly adjacent to the secretory cells of the end piece, and the lumen of the end piece is continuous with the lumen of the intercalated duct.The intercalated ducts are lined by a simple cuboidal epithelium,and myoepithelial cell bodies and their processes.The intercalated ducts contribute macromolecular components, which are stored in their secretory granules, to the saliva. These components include lysozyme and lactoferrin;

Intercalated duct cellThe intercalated duct cells have centrally placed nuclei and a small amount of cytoplasm containing some rough endoplasmic reticulum and a small Golgi complex A few small secretory granules may be found in the apical cytoplasm, especially in cells located near the end pieces. The apical cell surface has a few short microvilli projecting into the lumen; The lateral surfaces are joined by apical junctional complexes and scattered desmosomes and gap junctions and have folded processes that interdigitate with similar processes of adjacent cells.

Striated DuctsThe striated ducts, which receive the primary saliva from the intercalated ducts, constitute the largest portion of the duct system. These ducts are the main ductal component located within the lobules of the gland, that is, intralobular

striated ductsThe ducts have large lumina (Lu) and are lined by a pale-staining, simple columnar epithelial cells with centrally placed nuclei and faint basal striations.

SDLuStriated duct cellsThe basal striations of the duct cells are result from the presence of numerous elongated mitochondria, separated by highly infolded and interdigitated basolateral cell membranes;The apical cytoplasm may contain small secretory granules and electron-lucent vesicles;The granules contain kallikrein and perhaps other secretory proteins;The presence of vesicles suggests that the cells may participate in endocytosis of substances from the lumen;The duct cells contain numerous lysosomes and deposits of glycogen frequently are present in the perinuclear cytoplasm.Adjacent cells are joined by tight junctions and junctional complexes but lack gap junctions.

Excretory DuctsThe excretory ducts are located in the connective tissue septa between the lobules of the gland, that is, in an extralobular or interlobular location. These ducts are larger in diameter than striated ducts and typically have a pseudostratified epithelium with columnar cells extending from the basal lamina to the ductal lumen and small basal cells that sit on the basal lamina but do not reach the lumen.

Larger excretory ductAs the smaller ducts join to form larger excretory ducts, the number of basal cells increases, and scattered mucous cells may be present;A large excretory duct is surrounded by dense connective tissue. The pseudostratified epithelium contains several mucous goblet cells (arrowheads).

FORMATION AND SECRETION OF SALIVAThe formation of saliva occurs in two stages. In the first stage, cells of the secretory end pieces and intercalated ducts produce primary saliva, which is an isotonic fluid containing most of the organic components and all of the water that is secreted by the salivary glands. In the second stage, the primary saliva is modified as it passes through the striated and excretory ducts, mainly by reabsorption and secretion of electrolytes. The final saliva that reaches the oral cavity is hypotonic.

DUCTAL MODIFICATION OF SALIVAAn important function of the striated and excretory ducts is the modification of the primary saliva produced by the end pieces and intercalated ducts occurring principally through reabsorption and secretion of electrolytes.The luminal and basolateral membranes have abundant transporters that function to produce a net reabsorption of Na+ and Cl resulting in the formation of hypotonic final saliva.The ducts also secrete K+ and HCO3 but little if any secretion or reabsorption of water occurs in the striated and excretory ducts.

InterstitumH+

K+ClATPStriated duct cellK+Na+Na+TJLumenHCO3Na+Na+ClH+H2OCl

DUCTAL MODIFICATION OF SALIVARelease of water by the cells of the secretory end pieces is regulated principally by the parasympathetic innervation.The next step Ca2+ is released from intracellular stores.The increased Ca2+ concentration opens Cl channels in the apical cell membrane and K+ channels in the basolateral membrane.The apical Cl efflux draws extracellular Na+ into the lumen,through the tight junctions, to balance the electrochemical gradient. It results in the movement of water into the lumen via water channels in the apical membrane and through the tight junctions.Thus fluid secretion by the salivary glands is driven by the active transport of electrolytes.

InterstitumH+

K+ClATPStriated duct cellK+Na+Na+TJLumenHCO3Na+Na+ClH+H2OClElectrolyte composition of saliva and salivary flow rateThe final electrolyte composition of saliva varies, depending on the salivary flow rate.At high flow rates, saliva is in contact with the ductal epithelium for a shorter time, and Na+ and Cl concentrations rise and the K+ concentration decreases. At low flow rates the electrolyte concentrations change in the opposite direction.The HCO3 concentration, however, increases with increasing flow rates, reflecting the increased secretion of HCO3 by the acinar cells to drive fluid secretion.Electrolyte reabsorption and secretion by the striated and excretory ducts is regulated by the autonomic nervous system and by mineralocorticoids produced by the adrenal cortex.Macromolecular ComponentsThe cells of the secretory end pieces have abundant rough endoplasmic reticula and a large Golgi complex, and they store their products in membrane-bound granules in the apical cytoplasm.The secretory granules are stored in the apical cytoplasm until the cell receives an appropriate secretory stimulus. The granule membranes fuse with the cell membrane at the apical (luminal) surface, and the contents are released into the lumen by the process of exocytosis;The fusion of the granule membrane with the cell membrane is mediated by the formation of a protein complex involving proteins of the granule membrane, proteins of the cell membrane, and proteins in the cytoplasm. Following release of the granule content, the granule membrane is internalized by the cell as small vesicles, which may be recycled or degraded.MYOEPITHELIAL CELLSMyoepithelial cells are contractile cells associated with the secretory end pieces and intercalated ducts of the salivary glands;These cells are located between the basal lamina and the secretory or duct cells and are joined to the cells by desmosomes;Myoepithelial cells have many similarities to smooth muscle cells but are derived from epithelium.

MYOEPITHELIAL CELLS

Basal laminaMyoepithelialcellSecretoryend pieceIntercalatedductSecretory cellMyoepithelial cellsMyoepithelial cells present around the secretory end pieces have a stellate shape;Numerous branching processes extend from the cell body to surround and embrace the end piece ;The processes are filled with filaments of actin and soluble myosin.

Control of the secretionSecretion of saliva is under control of the autonomicnervous system, which controls both the volume and type of saliva secreted. This is actually fairly interesting: a dog fed dry dog food produces saliva that is predominantly serous, while dogs on a meat diet secrete saliva with much more mucus. Parasympathetic stimulation from the brain, as was well demonstrated by Ivan Pavlov, results in greatly enhanced secretion, as well as increased blood flow to the salivary glands.Potent stimuli for increased salivation include the presence of food or irritating substances in the mouth, and thoughts of or the smell of food. Knowing that salivation is controlled by the brain will also help explain why many psychic stimuli also induce excessive salivation - for example, why some dogs salivate all over the house when it's thundering.Composition of the saliva organic elementsinorganic elementsproteins;amino acids;enzymes;immunoglobulins;glucose;lactates;citrate;ammonia;urea;creatinine;Cholesterol.calcium;phosphorus;sodium;potassium;magnesium;fluorine;chlorides;bicarbonates;Phosphates.SalivaHuman saliva is 99.5%water, while the other 0.5% consists ofelectrolytes, mucus,glycoproteins,enzymes, andantibacterialcompounds such as secretoryIgA andlysozyme.

Electrolytes:221mmol/Lsodium(lower thanblood plasma);1036mmol/Lpotassium (higher than plasma);1.22.8mmol/Lcalcium (similar to plasma);0.080.5mmol/Lmagnesium;540mmol/Lchloride(lower than plasma);25mmol/Lbicarbonate(higher than plasma);1.439mmol/Lphosphate;Iodine- usually higher than plasma, but dependent variable according to dietary iodine intake.

Organic components of SalivaEnzymes:Amylase converting starch into glucose and fructose;Lyzozymes prevents bacterial infection in the mouth;Histatins prevents fungal infections;Secretory IgA immunity mediator.

MucusMucus in saliva mainly consists ofmucopolysaccharidesandglycoproteins;Glycoprotein (Mucins)Lubricant;Types MG1 and MG2;Polypeptide chain that stick together;Low solubility, high viscosity, strong adhesiveness;Aids in mastication, speech, swallowing by lubrication.Glycoprotein (Mucins)Preserve mucosal integrity;Protective barrier by excessive wear;Antibacterial action by selective adhesion of microbes to oral tissue surface;Barrier against acid penetration.MG1High molecular wt;Adsorbs tightly to the tooth surface enamel;Pellicle formation protection from acid challenges;High in caries susceptible patients.

MG2Low molecular wt;Binds to enamel but get displaces easily;Promotes the aggregation and clearance of oral bacteria (S. mutans);High in caries resistant cases.

Antibacterial compounds and growth factorAntibacterial compounds (thiocyanate,hydrogen peroxide, and secretoryimmunoglobulin A);Epidermal growth factoror EGF.

Antimicrobialenzymes that kill bacteriaLysozyme;Salivarylactoperoxidase;Lactoferrin;Immunoglobulin A.There are three major enzymes found in saliva:-amylase or ptyalin, secreted by the acinar cells of the parotid and submandibular glands, starts the digestion of starch before the food is even swallowed. It has apHoptima of 7.4;Lingual lipase is secreted by the acinar cells of the sublingual gland, has apHoptimum ~4.0 so it is not activated until entering the acidic environment of the stomach; Kallikrein is a vasodilator. It is secreted by the acinar cells of all three major salivary glands.

-AmylasePresent in parotid saliva at conc. of 60-120 mg/100ml; in submandibular saliva at approx. 25 mg/100 ml;Very little amylase activity in the sublingual and minor glandular secretions;6 isoenzyme forms exist. Alpha-amylase is Ca dependent and readily inactivated by a pH of 4 or less;The enzyme hydrolyses the alpha 1:4 glycosidic bond between glucose units in the polysaccharide chain of starch.EnzymesLactoperoxidase stimulation of minor salivary glands;RNA and DNA cellular maintenance;Lipase iniciates digestion of fat;

LyzozymeAn antibacterial enzymes;The mean concentration in whole saliva:Resting 22 mg/100ml;Stimulated 11 mg/100 ml;Lyzozyme acts on the B(1-4) bond between N-acetyl-muramic acid and N-acetyl glucosamin in the Gram+ bacterial cell wall component;Lyzozyme may also be bactericidal;Inhibits mucosal colonization by microbial aggregation.

EnzymesKallikreinSplits serum beta-globulin into bradykinin;Functional vasodilatation to supply an actively secreting gland;DextranasesIncreased whole saliva dextranase levels may be associated with impaired oral hygiene and over consumption of sucrose and related fermentable carbohydrates which support the growth of organisms producing dextranases.

InvertasesHigh invertase activity is based on the involvement of several enzymes chiefly derived from dental plaque S. Mutans and S. Salivarius;High invertase activity consume high sucrose and it usually parallels with high lactobacillus and streptococcus count of plaque.Prolin-rich proteinsProline-rich proteins have function inenamelformation, Ca2+-binding, microbe killing and lubrication.Minor enzymesInclude: salivaryacid phosphatasesA+B;N-acetyl-alanine amidase;NAD(P)H dehydrogenase;superoxide dismutase;transferase; aldehyde dehydrogenase;glucose-6-phosphate isomerase, and tissuekallikrein(function unknown).

Cells:Possibly as many as 8 million human and 500 million bacterial cells per mL; The presence of bacterial products (small organic acids, amines, and thiols) causes saliva to sometimes exhibitfoul odor.Cellular CompositionThe cellular composition consists of:Epithelial cells;Neutrophils;Lymphocytes;Bacterial flora.OpiorphinOpiorphin, a newly researched pain-killing substance found in human salivaHaptocorrina protein which binds toVitamin B12 to protect it against degradation in the stomach, before it binds to Intrinsic FactorIndividual HydrationThe degree of individual hydration is the most important factor that interferes in salivary secretion; When the body water content is reduced by 8%, salivary flow virtually diminishes to zero, whereas hyperhydration causes an increase in salivary flow.During dehydration, the salivary glands cease secretion to conserve water.

Factors Influencing Salivary Flow and Composition

Several factors may influence salivary flow and its composition. As a result, these vary greatly among individuals and in the same individual under different circumstances.Body Posture, Lighting, and SmokingPatients kept standing up or lying down present higher and lower SF, respectively, than seated patients.There is a decrease of 30% to 40% in SF of people that are blindfolded or in the dark. However, the flow is not less in blind people, when compared with people with normal vision. This suggests that blind people adapt to the lack of light that enters through the eyes. Olfactive stimulation and smoking cause a temporary increase in unstimulated SF.

The Circadian and Circannual CycleSF attains its peak at the end of the afternoon but goes down to almost zero during sleep. Salivary composition is not constant and is related to the Circadian cycle.The concentration of total proteins attains its peak at the end of the afternoon, while the peak production levels of sodium and chloride occur at the beginning of the morning.According to Edgar, the circannual rhythm also influences salivar secretion. In the summer lower volumes of salivary flows from the parotid gland, while in the winter there are peak volumes of secretion. Thinking of Food and Visual StimulationThinking of food or looking at food are weak salivation stimuli in humans. It may seem that people salivate simply because of thinking of food, but in reality they become more conscious of the saliva in the floor of the mouth between swallows. Some researchers observed a small increase in SF in the face of visual stimuli, while others observed no effect whatever.MedicationsMany classes of drugs, particularly those that have anticholinergic action (antidepressants, antipsychotics, antihistaminics, and antihypertensives) may cause reduction in SF and alter its composition.Regular Stimulation of Salivary FlowThere is evidence regular stimulation of SF with the use of chewing gum leads to an increase in stimulated SF.

Size of Salivary Glands and Body WeightStimulated SF is directly related to the size of the salivary gland, contrary to unstimulated SF which does not depend on its size;

Unstimulated SF appears to be independent of body weight;On the other hand, obese boys presents significantly lower salivary amylase concentration in comparison with controls.Salivary Flow IndexThe main factor affecting salivary composition is the flow index which varies in accordance with the type, intensity, and duration of the stimulus. As the SF increases, the concentrations of total protein, sodium, calcium, chloride, and bicarbonate as well as the pH increases to various levels, whereas the concentrations of inorganic phosphate and magnesium diminish.Mechanical or chemical stimulus is associated with increased salivary secretion. The action of chewing something tasteless itself stimulates salivation but to a lesser degree than the tasty stimulation caused by citric acid. Acid substances are considered potent gustatory stimuli.

Physical ExercisePhysical exercise can alter secretion and induces changes in various salivary components, such as:immunoglobulins, hormones, lactate, proteins, and electrolytes.In addition to the determined intensity of the exercise, there is a clear rise in salivary levels of -amylase and electrolytes (especially Na+).During physical activities sympathetic stimulation appears to be strong enough to diminish or inhibit salivary secretion.Systemic Diseases and NutritionIn some chronic diseases such as: pancreatitis, diabetes mellitus, renal insufficiency, anorexia, bulimia, and celiac disease, the amylase level is high; Alterations in the psycho-emotional state may alter the biochemical composition of saliva.Depression is accompanied by diminished salivary proteins.Nutritional deficiencies may also influence salivary function and composition.Fasting and NauseaAlthough short-term fasting reduces SF it does not lead to hyposalivation, and the flow is restored to normal values immediately after the fasting period ends. Stimulated SF increases when preceded by gustatory stimulation in less than one hour before saliva collection. Saliva secretion increases before and during vomitingAgeDespite numerous studies on salivary secretion the effect of aging on SF remains obscure; However, functional studies among healthy individuals indicate aging itself does not necessarily lead to diminished capacity to produce saliva.GenderThe differences in salivary secretion between men and women have been attributed to two theories: women present smaller salivary glands in comparison with men and the female hormonal pattern may contribute to diminished salivary secretion.Contributions of Different Salivary GlandsOther factors that influence total salivary composition are the relative contribution of the different salivary glands and the type of secretion. The percentage of contribution by the glands during unstimulated SF is as follows:20% by the parotid glands;65%-70% submandibular glands; 7% to 8% sublingual glands;