Physiology of Saliva

Saliva

• Saliva is alkaline liquid secreted by the salivary glands and the mucous membrane of the mouth.

• Its principal constituents are water, mucus, buffers and enzyme.

• Function: to keep the mouth moist, to aid swallowing of food, to minimize changes of acidity in the mouth and to digest starch.

1. Parotid Gland2. Submandibular Gland3. Sublingul Gland

Anatomy and Physiology of Salivary Gland

Salivary Glands• The principle glands of salivation

are:– Parotid glands– Submandibular glands– Sublingual glands– Minor salivary glands

• In the salivary glands, the secretory granules containing the salivary enzymes are discharged from the acinar cells into the ducts.

• pH of saliva secreted : 7.0• Secretion : 1500mL per day

Parotid Gland• The largest salivary gland• Located anterior and inferior to

the ears in the subcutaneous regions of the cheek

• The Parotid has been described as having 5 processes (3 superficial and 2 deep).

• 80% overlies the masseter muscle.

• 20% on retromandibular

• The boundaries of the parotid compartment: – Superior border – Zygoma – Posterior border – External Auditory Canal – Inferior border – Styloid Process, Styloid Process

musculature, Internal Carotid Artery, Jugular Veins – Anterior border – a diagonal line drawn from the

Zygomatic root to the EAC • Facial nerve enters the parotid fossa by

passing between the stylohyoid muscle and the posterior belly of the digastrics muscle, then splits the gland into a superficial lobe & a deep lobe.

Nerves and Arteries

Submandibular Glands

• Submandibular gland lie along the body of the mandible.

• Submandibular duct arise from the portion of the gland that lies between the mylohoid and the hyoglossus muscle.

• The arterial supply of the mandible glands is from the submental branch of facial artery.

• Innervation to the Submandibular gland derives from 2 important sources: 1. Sympathetic innervation

from the Superior Cervical ganglion via the Lingual artery, and

2. Parasympathetic innervation from the Submandibular ganglion, which is fed by the Lingual nerve.

Sublingual Glands

• Smallest and most deeply situated.

• Lies in the floor of the mouth between the mandible and the genioglossus muscle.

• Numerous small sublingual ducts open into the floor of the mouth along the sublingual folds.

• The arterial supply of this gland is from:– The sublingual branch of lingual artery.– The submental branch of facial artery.

• Innervation to the Sublingual gland derives from 2 important sources: 1. Sympathetic innervation from the cervical chain

ganglia via the Facial artery.2. Parasympathetic innervation, like the

Submandibular gland, is derived from the Submandibular ganglion.

Minor Salivary Glands• The minor salivary glands lack a branching network of

draining ducts. • Each salivary unit has its own simple duct. • The minor salivary glands are concentrated in the Buccal,

Labial, Palatal, and Lingual regions. • Found at the superior pole of the tonsils (Weber’s glands), the

tonsillar pillars, the base of tongue (von Ebner’s glands), paranasal sinuses, larynx, trachea, and bronchi.

• Most of the minor glands receive parasympathetic innervation from the Lingual nerve, except for the minor glands of the palate, which receive their parasympathetic fibers from the Palatine nerves, fed by the Sphenopalatine ganglion.

Composition of Saliva

1% - ions and organic components99% - water

Inorganic Component

• Most important cations : sodium and potassium• Major osmotically active anions : chloride and

bicarbonate.• Other electrolytes : calcium phosphate, fluoride,

thiocyanate, magnesium sulfate, and iodine.• Water and the ionic constituents of saliva are

derived by translocation from blood plasma.• But saliva is not merely an ultrafiltrate of

plasma.

Organic Component

1. Amylase: Glycosylated and nonglycosylated.

2. Lipase Secreted by the lingual (von Ebner’s)salivary glands.

3. Mucosa glycoprotein Consist of multiple oligosaccharide chain attached to a peptide

core.

4. Proline-rich glycoproteinI. Basic glycoprotein : binds lipids and may preferentially absorb to

membranesII. Acidic protein : comprises calcium binding proteins and attaches

to the tooth surface

5. Tyrosine-rich protein (statherin) Prevent calcium precipitating from saliva

6. Histadine-rich protein Forms pellicle

7. Lysozyme Important in oral protective functions

8. Secretory immunoglobulin A Synthesized by plasma cell

9. Growth factors and kallikrein

Factors Affecting Salivary Secretion

• Secretion of saliva is under nervous control and to date no hormones directly affecting the rate of salivary secretion have been identified.

• Increase secretion my result from conditional reflex.

• Increased secretion when:– The noise of food being prepared– Talking about food– Sight of food

• Secretion decrease when:– Though about disliked food

• Unconditional reflex and increase secretion may be caused by:– Taste. – Smell. – Mechanical stimulation of the oral mucosa– Mechanical irritation of the gingiva– Mastication of food– Chemical irritation of the oral mucosa– Distention or irritation of esophagus– Chronic irritation of the esophagus– Chemical irritation of the stomach– Pregnancy

Function of salivaPlay essential role during mastication in bolus formation.Act as a lubricant in swallowing.Speech production.Digestion•Salivary amylase is a digestive enzyme- breakdown of starch and glycogen.•Salivary lipase-secreted by lingual salivary glands(von Ebner’s gland)-fat digestion.Temperature regulationBuffering action•Maintenance of oral health by limiting the formation of acid from bacterial fermentation

• Maintaining the integrity of oral and dental tissue by controling the oral pH

• Bicarbonate -major factor to control the pH.• Reduction in salivary flowpH etching & dissolution

of crowns of teeth. Antibacterial action & Antifungal action• Lysozyme,lactoferrin,sialoperoxidase help against

pathogenic microorganisms • Immunoglobulins and secretory IgA also act against

microorganisms. Production of growth factors & other regulatory

peptides. Remineralization• Saliva is supersaturated with ions,which facilitate

remineralization of teeth

Agglutination• immunoglobulins and secretory IgA cause

agglutination of specific microorganisms- prevent their adherence to oral tissues.

• Mucins as-specific agglutinins to aggregate microorganisms.

Taste• Saliva has a low threshold concentration of sodium

chloride,sugar,urea etc allowing perception of taste to occur.

• It acts as a solvent allowing mixing and interaction of food with taste buds

Mechanism of saliva secretion is controlled by the autonomic nervous system.Salivary glands have both parasympathetic and sympathetic

secretomotor innervation.

A)Parotid glandi)Parasympathetic control otic ganglion is a parasympathetic ganglion located just below

the foramen ovale and medial to the mandibular nerve to which it is connected.

The lesser superficial petrosal nerve(branch of glossopharngeal nerve), carries preganglionic parasympathetic fibers from the inferior salivatory nucleus synapse in the otic ganglion.

Postganglionic fibers reach the gland via the auriculotemporal branch of the mandibular nerve.

ii)Sympathetic controlArises in the 1st 2 thoracic segment(T1 and T2) &

synapse in the sympathetic superior cervical ganglion.

Postganglionic fibersotic ganglion via middle meningeal artery.

Sympathetic fibers pass through the otic ganglion without synapsing and accompany parasympathetic fibers gland

B) Submandibular & sublingual glandsi)Parasympathetic controlSubmandibular ganglion is a small parasympathetic

ganglion located in the floor of the mouth& is connected to lingual nerve.

Preganglionic fiber from superior salivatory nucleus ganglion via facial nerve.

Postganglionic fibers from this ganglion are secretomotor to both glands.

ii)Sympathetic control similar route to the parotid glandPostganglionic fiberssubmandibular ganglion via

facial and lingual arteries.And pass through the ganglion without synapsing to

supply the submandibular & sublingual glands

C) Minor salivary glandsi)Parasympathetic controlMost of the palate are supplied by parasympathetic

fibers arising in superior salivatory nucleus.

Preganglionic fiberparasympathetic sphenopalatine ganglion, situated in pterygopalatine fossa and connected to the maxillary nerve.

Postganglionic fibers from the sphenopalatine ganglion reach the glands of the palate via palatine branches of maxillary nerve.

C-pterygopalatine fossa

ii)Sympathetic controlSympathetic fibers pass to the glands of palate from

the1st 2 thoracic segments(T1&T2).Preganglionic fiber synapse in the superior cervical

ganglion from where postganglionic fibers parasympathetic sphenopalatine ganglion via maxillary nerve.

sphenopalatine ganglion

• Both the superior(associated with facial nerve) & inferior salivatory nuclei(associated with glossopharyngeal nerve) are found in medulla oblongata.

• Parasympathetic innervation is secretory & vasodilatory; Sympathetic innervation is vasoconstrictive.

• Secretory activity of gland cells is mediated by cholinergic(parasympthetic) and adrenergic(sympathetic)agents.

Following statement can be made with regard to autonomic secretory innervation of salivary glands

1. Secretory cells are supplied by both parasympathetic & sympathetic nerves

2. Impulses conducted via parasympathetic system are more regular than impulses along sympathetic nerves.

3. The effect of stimulation by nerves of these 2 systems is not necessarily antagonistic.

4. Both stimulation causes contraction of myoepithelial cells- promote salivary flow.

5. Blood capillaries receive stimuli from both systems, but parasympatheticvasodilation; sympathetic vasoconstriction

• Parasympathetic stimulation is mainly responsible for secretion of larger volume of saliva by secretory cells;Sympathetic has greater influence on the composition of saliva.

Types of salivary gland

Major salivary glandMinor salivary gland

Major salivary glandsParotid gland:•Pure serous gland•Found in adult human, although mucous cells present in children.

Submandibular gland: •Mixed. •Predominantly serous. •Serous mucous ratio is 12:1.

Sublingual gland: •Mixed. •Predominantly mucous. •A few pure serous acini and the serous cells present are arranged in demilunes.

Minor salivary glands1. Lingual glands

• Found bilaterally.

Anterior lingual gland• Inferior surface of

tongue tip

Anterior mucous

Posterior mixed

Posterior lingual gland• Found in lingual tonsil and lateral margin of the

tongue• Pure mucous gland

2. Buccal and labial glands• Found in cheeks

and lips.• May contain both

mucous and serous.

3. Palatine gland• Pure mucous gland• Found in:

• Soft palate• Uvula• Posterolateral

of hard palate

4. Glossopalatine glands

• Pure mucous glands

• Found in glossopalatine fold.

Salivary gland radiography

Submandibular gland

•Seen in posterior part of submandibular triangle•Triangular in shape•May be connected with parotid or sublingual gland by glandular processes•Wharton duct runs from hilum at the level of mylohyoid muscle, bends around free part of mylohyoid, extends to its orifice at sublingual caruncle along the medial part of the sublingual gland

Wharton duct:• Efferent duct of

submandibular gland

Parotid gland

•Located in retromandibular fossa, anterior to ear and SCM•Located at mandibular angle wrapping it•Majority is superficial to masseter•Drained by Stenson duct - exits above upper 2nd molar tooth; usually not seen on USG

Stensen’s duct:• Efferent duct of

parotid gland

• Lies between muscles of floor of oral cavity

• Lies adjacent to mandible

• Oval on cross section and lentiform on long axis

• Medially there is Wharton duct

Sublingual glands

Duct calculi

Parotid gland

•Calculus in the distal segment of the partoid duct (arrow). •Sialography

Duct calculiSubmandibular gland

•Axial CT demonstrating two closely apposed calculi at the hilus of the right submandibular gland(arrow).

•Lateral oblique plain film demonstrating a radiopaque calculus(arrow).

Radiographic projection

Lateral Oblique Projection:•To delineate the submandibular gland•Image is projected below the ramus of the mandible

Lateral Projection:•Shows ductal projection

Occlusal Projection:•Useful for sialolith located in the anterior part of the wharton’s duct

Anterior-posterior projection:•Demonstrates medial and lateral gland structures

Panaromic Projection•Made during the filling phase.•Easier to expose•Low radiation•Satisfactory bony details

Applied diagnostic imaging of salivary gland

1. Plain film radiography2. Intraoral radiography3. Extraoral radiography4. Conventional sialography5. Computed tomography (CT)6. Magnetic resonance imaging (MRI)7. Ultrasonography (US)

1. Plain Film Radiography

• Provide sufficient information to preclude the use of more sophisticated and expensive imaging techniques.

• To identify inrelated pathoses in the areas of the salivary glands

• To suggest present of sialoliths :– 20% in submandibular not well calcified,– 40% in parotid radiolucent, not visible.– Rarely found in sublingual

• A large proportion of salivary calculi are radiopaque

• Patients presenting with obstructive symptoms of acute intermittent swelling require routine radiographs to determine the presence and position of the stone (s).

2. Intraoral radiography

• In submandibular gland:– Anterior 2/3: Sialoliths are imaged with a cross sectional

mandibular projection– Posterior: posterior oblique view. Central ray is directed

parallel with mandible.• In parotid gland:– More difficult to demonstrate – Stensen duct– Only sialoliths in anterior part can be imaged. To

demonstrate:• Held intraoral film packet inside the cheek as high as posible in

buccal sulcus and over parotid papilla.• Central ray is perpendicular to the film centre.

3. Extraoral radiography• In submandibular gland:

– Demonstrate: • Posterior duct sialoliths• Intraglandular sialoliths

– To demonstrate, lateral projection:• Open mouth, extend chin, depress tongue: sialolith move inferior to mandibular

border

• Parotid gland:– Demonstrate:

• Interglandular sialoliths

– To demonstrate: Cheek puffed out: sialolith move out of bone– Sialoliths superimposed over the ramus and body of mandible: limited

value of lateral radiograph– Sialoliths in distal portion of stensen duct: difficult to demonstrate by

intraoral and lateral

4. Conventional saliography• Definition: Radiographic demonstration of the major

salivary glands by introducing a radiopaque contrast medium into their ductal system.

• Radiopaque contrast agent is used before imaging.• Most detailed way to image ductal system• “Scout film”: used before infusion of contrast solution

– Verifying optimal exposure factors– Patient positioning parameters– Detect radiopaque sialoliths– Extraglandular pathosis

• Contrast agent:– Lipid-soluble: ethiodol– Non-lipid-soluble: sinografin

• To opacify the salivary duct of interest and associated glandular tissues to demonstrate potential pathological processes.

• The administration of contrast fills the salivary duct and flows distal to the intraglandular ducts to outline the salivary gland.

• Due to the close proximity of the three pair of salivary glands, only one of the salivary ducts and its gland can be imaged at a time.

Normal saliographic appearance

Parotid gland• The main duct is of even diameter (1-2 mm wide) and should be filled

completely and uniformly.• The duct structure within the gland branches regularly and tapers gradually

towards the periphery of the gland.• Tree in winter appearance.

Submandibular gland• The main duct is of even diameter (3-4 mm wide) and should be

filled completely and uniformly.• Smaller than parotid, but the overall appearance is similar with

the branching duct structure tapering gradually towards the periphery.

• Bush in winter appearance

Sialography Procedure

1. Localization of the orifice of the selected duct. Palpate the salivary gland or ask the patient to suck on a lemon slice.

2. The duct may be accessed with a lacrimal probe for cannulization.

3. The selected cannula should be filled with the contrast to ensure that no air is injected into the duct.

4. The cannula should be immobilized through the placement of sterile gauze between the cannulated sites and the tongue.

5. The extension tubing and contrast-filled syringe may then be secured to the chest by adhesive tape.

6. The contrast medium is then introduced.

The Contrast Medium• A radiopaque iodinated substance.1. Lipid soluble• 37% iodine• ADVANTAGES:-

• It is not diluted by saliva• It is not absorbed across glandular mucosa• Highly opaque• Provides optimal visualization of ducts.

• DISADVANTAGES:-• More viscous , higher injection pressure is required• More pain & discomfort• Not to be used if the calculi are suspected since it may

inhibit the visualization of stone.

The Contrast Medium 2. Water soluble• 28 to 38% iodine• Routinely used. • ADVANTAGES:-

• Low viscosity• Low surface tension• More miscible with salivary secretions• Residual contrast medium is absorbed and excreted

through kidney

• DISADVANTAGES:-• Opacification worst than oil –based media as it is rapidly

absorbed across glandular mucosa• It is diluted by saliva• The injection is accompanied by little pain & discomfort

5. Compured tomography (CT)

• Evaluate structures in and adjacent to salivary glands.

• Display both soft and hard tissues.• Parotid glands are more radiopaque than the

fat but less opaque than muscle.• Submandibular and sublingual gland are

identified on the basis of shape and location.

Advantages

• Less invasive than sialography • Does not require the use of contrast material• Used for assessment of mass lesions of the

salivary glands• Can demonstrate salivary gland calculi.

Especially submandibular stones that are located posteriorly in the duct, at the hilum of the gland or in the substance of gland itself.

6. Magnetic resonance imaging (MRI)• MRI is superior to CT scanning in delineating the soft

tissue detail of the salivary gland lesions• Advantages:– Better images of soft tissue than CT– Disclose the major vessels– Identified as areas of no tissue signal (dark), without

contrast medium.– Accurately reveal ductal morphology– No radiation exposure to patient

• Disadvantage:– May not be sufficiently sensitive to identify small sialoliths.

7. Ultrasonography (US)

• Differentiate solid masses and cystic• Detect sialoliths and diagnose advanced

autoimmune lessions.• Advantages:– Inexpensive compare to CT and MRI– Widely available– Painless– Easy to perform– Noninvasive

Salivary gland disorders

Parotid gland

Unilateral•Bacterial sialadenitis•Sialodochitis•Cyst•Benign neoplasm•Malignant neoplasm•Intraglandular lymph node•Masseter muscle hypertrophy•Lesions of adjacent osseous structures

Bilateral•Bacterial sialadenitis•Viral sialadenitis•Sjogren syndrome•Warthin hypertrophy•Medicated-induced hypertrophy•Accesory salivary glands•TMJ-related lesions

Submandibular gland

Unilateral•Bacterial sialadenitis•Sialodochitis•Cyst•Benign neoplasm•Malignant neoplasm•Fibrosis

Bilateral•Bacterial sialadenitis•Sjogren syndrome•Lymphadenitis•Branchial cleft cyst•Submandibular space infection

Sialolithiasis

• Synonyms: Calculus and salivary stone• Definition: formation of a calcified obstruction

within salivary duct• Radiographic features:– May appear either radiopaque or radiolucent– Vary in shapes– Homogenous radiopaque internal structure– Contrast agent is more radiopaque and is used to

obscure small and radiolucent sialoliths

Sialolithasis

CT appearance of Sialolithasis

Contrast-enhanced CT of the neck demonstrates a stone (blue arrow) in the submandibular region of a dilated Wharton's Duct (red arrow)

Sialographic appearances of sialodochitis• Segmented sacculation or dilatation and stricture of the main duct•Sausage link appearance• Associated calculi or ductal stenosis.

Sialolithiasis• May appear either radiopaque or radiolucent on radi-ographic examinations

(20% to 40% of cases), depending on their degree of calcification• Vary in shape from long cigar shapes to oval or round shapes. • When visible, they usually have a homogeneous radiopaque internal structure. • Sialography is helpful in locating obstructions that are undetectable with

plain radiography, especially if the sialoliths are radiolucent.

Sjogen’s syndrome• Widespread dots or blobs of contrast medium within the gland, an appearance known as

punctate sialectasis or snowstorm. This is caused by a weakening of the epithelium lining the intercalated ducts, allowing the escape of the contrast medium out of the ducts.

• Considerable retention of the contrast medium during the emptying phase• The main duct is usually normal.

Dermoid cyst or ranula

• More radiopaque soft tissue of this cyst compared with surrounding soft tissue.

Mucoceles• About 90% of mucoceles occur in the ethmoidal and frontal sinuses and

are rare in the maxillary and sphenoid sinuses.• The normal shape of the sinus is changed into a more circular shape as

the mucocele enlarges.• The internal aspect of the sinus cavity is uniformly radiopaque.