SALIVA

1. SALIVA

2. Contents: • Introduction • Salivary gland anatomy • Functions of saliva • Secretion of saliva • Composition of saliva • Organic components • Inorganic components • Hypofunction of salivary glands • Xerostomia • Ptyalism • Burning mouth syndrome • Saliva:A diagnostic fluid • Diagnostic imaging of salivary glands

3. Saliva lacks the drama of blood,the emotion of tears and toil of sweat but it still remains one of the most important fluids in the human body. • Its status in the oral cavity is at par with that of blood i.e. to remove waste,supply nutrients and protect the cells

4. What is saliva? • Saliva is composed of more than 99% water and less than 1% solids,mostly electrolytes and proteins,the latter giving saliva its characteristic viscosity • The term saliva refers to the mixed fluid in the mouth in contact with the teeth and oral mucosa,which is often called ‘whole saliva’ • Normally the daily production of whole saliva ranges from 0.5 to 1.0 litres

5. 90% of the whole saliva is produced by three paired major salivary glands • Parotid Gland • Submandibular gland • Sublingual gland

6. Secretions from many minor salivary glands in the oral mucosa (labial,lingual,palatal,buccal,glossopalatine and retromolar glands) also contribute (less than 10%) to the saliva secretion • In addition,whole saliva contains contributions from non-glandular sources such as gingival crevicular fluid in an amount that depends on the periodontal status of the patient

7. Whole saliva,in contrast to glandular saliva,also contains vast amounts of epithelial cells from the oral mucosa and millions of bacteria. These components give whole saliva its cloudy appearance,which is different from glandular saliva, which is transparent like water.

8. Salivary gland anatomy Parotid gland: • Largest of all the salivary glands • Purely serous gland that produce thin,watery amylase rich saliva • Superficial portion lies in front of external ear & deeper portion lies behind the ramus of mandible • Stensen's Duct (Parotid Papilla) • Opens out adjacent to maxillary second molar

9. Submandibular gland • Second largest salivary gland • Mixed gland • Located in the posterior part of floor of mouth,adjacent to medial aspect of mandible & wrapping around the posterior border of mylohyoid muscle • Wharton's Duct • Opens beneath the tongue at sub-lingual caruncle lateral to the lingual frenum

10. Sublingual gland: • Smallest salivary gland • Mixed gland but mucous secretory cells predominate • Located in anterior part of floor of mouth between the mucosa and mylohyoid muscle • Opens through series of small ducts (ducts of rivinus) opening along the sub-lingual fold & often through a larger duct(bartholin’s duct) that opens with the wharton’s duct at the sub-lingual caruncle

11. Multifunctionality Amylases, Cystatins, Histatins, Mucins, Peroxidases Carbonic anhydrases, Histatins Anti- Bacterial Buffering Amylases, Mucins, Lipase Cystatins, Mucins Anti- Viral Digestion Salivary Functions Mineral- ization Anti- Fungal Cystatins, Histatins, Proline- rich proteins, Statherins Histatins Lubricat- ion &Visco- elasticity Tissue Coating Amylases, Cystatins, Mucins, Proline-rich proteins, Statherins Mucins, Statherins

12. MAJOR FUNCTIONS OF SALIVA • Fluid or Lubricant Saliva coats the mucosa & helps to protect against mechanical,chemical and thermal irritation. It also assists smooth airflow,speech & swallowing. • Buffering Saliva helps to neutralise plaque pH after eating thus reducing time for demineralization caused by bacterial acids produced during sugar metabolism • Remineralization Saliva is supersaturated with ions,which facilitate remineralization of teeth

13. Digestion • Breakdown of starch-amylase • Fat-lingual lipase • Moistening and lubricative properties of saliva:allow the formation & swallowing of food bolus • Anti-microbial action • Lysozyme,lactoferrin,sialoperoxidase help against pathogenic microorganisms specifically • Immunoglobulins and secretory IgA also act against microorganisms.

14. Cleansing Clears food and aids swallowing. • Agglutination immunoglobulins and secretory IgA cause agglutination of specific microorganisms, preventing their adherence to oral tissues. Mucins as well as specific agglutinins also aggregate microorganisms.

15. Pellicle formation Derived from salivary proteins,it forms a protective diffusion barrier to acids from plaque. • 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

16. Water balance Osmoreceptors act as per state of hydration of the body to transmit information to the hypothalamus • Tissue repair A variety of growth factors & other biologically active peptides and proteins are present in small quantities in saliva.under experimental conditions,many of these promote tissue growth & differentiation,wound healing and other beneficial effects.

17. Regulation of saliva secretion Afferent signals from sensory receptors in mouth Trigeminal,facial,glossopharyngeal nerves Salivary nuclei in the medulla oblongata of brain Parasympathetic nerve bundle sympathetic nerve bundle salivary glands

18. Innervation • Parasympathetic innervation to major salivary glands • Otic ganglion fibers supply Parotid Gland • Submandibular ganglion supplies other major glands • Sympathetic innervation promotes saliva flow • Stimulates muscle contractions at salivary ducts

19. Saliva secretion is also controlled by the conditioned reflexes. • Besides receiving impulses from the afferents,the salivary nuclei also receives impulses from higher centers of brain which leads to release of variety of neurotransmitters resulting in facilatory or inhibitory effects • As a result of such control,unstimulated salivation is inhibited during sleep,fear & mental depression • Stress may increase or decrease salivary flow

20. THE SECRETORY UNIT The basic building block of all salivary glands • ACINI - water and ions derived from plasma • Saliva formed in acini flows down DUCTS to empty into the oral cavity.

21. Salivary secretion:two step model • Formation of primary saliva: • Initiated by binding of neurotransmitters in the acinar cell membranes • Acinar cell loses K⁺ to the interstitium & Cl⁻ to the lumen • Gain of Cl⁻ creates negative potential in the lumen,driving interstitial Na⁺ into lumen thereby restoring electroneutrality • Water flux follws the movement of salt into the lumen for osmotic reasons,resulting in acinar cell shrinkage • Outcome is the formation of isotonic primary saliva

22. Ductal modification of primary saliva: • Occurs principally through reabsorption & secretion of electrolytes • The luminal & basolateral membrane have abundant transporters that function to produce a net reabsorption of Na⁺ & Cl⁻ resulting in formation of hypotonic final saliva • The final electrolyte composition of saliva varies depending on the salivary flow rate

23. At high flow rates,saliva is in contact with the ductal epithelium for shorter time & Na⁺ & Cl⁻ concentration increase & K⁺ concentration decrease • At low flow rates,the electrolyte concentration change in the opposite direction • The HCO₃⁻ concentration increases with increased flow rates,reflecting the increased secretion of HCO₃⁻ by the acinar cells to drive fluid secretion

24. TWO STAGE HYPOTHESIS OF SALIVA FORMATION Most proteins Na+ Cl-resorbed Hypotonic final saliva into mouth Water & electrolytes Someproteinselectrolytes K+secreted Isotonic primary saliva

25. Saliva production • Differential saliva production by glands • Unstimulated salivation (Salivary gland at rest) • 1.5 Liters produced per day (basal rate) • Major salivary glands: 90% of saliva produced • Submandibular and sublingual glands: 70% of saliva • Stimulated salivation • Saliva production increases 5 fold • Parotid gland produces majority of saliva

26. Flow rate (ml/min)

28. Testing of saliva production • Unstimulated production – collection of saliva into container during 15 min • Stimulated production – collection of saliva during 5 min of chewing 1g paraffin • Unstimulated whole saliva flow rates of <0.1 ml/min. and stimulated whole saliva flow rate’s of <1.0 ml/min. are considered abnormally low& indicative of marked salivary hypofunction.

29. Recent work in Sjogren syndrome is beginning to identify changes in salivary cytokine & other protein levels that may have diagnostic significance . • Saliva may play a greater diagnostic role in monitoring for the presence and concentrations of drugs of abuse and therapeutic agents.

30. COMPOSITION OF SALIVA

31. Inorganic components Saliva compositon

32. Calcium and phosphate • Help to prevent dissolution of dental enamel • Calcium • 1.4 mmol/lt. (1.7 mmol/lt. in stimulated saliva) • 50% in ionic form • sublingual > submandibular > parotid • Phosphate • 6 mmol/lt. (4 mmol/lt. in stimulated saliva) • 90% in ionic form • pH around 6 - hydroxyapatite is unlikely to dissolve • Increase of pH - precipitation of calcium salts => dental calculus

33. Hydrogen Bicarbonate • Buffer • Low in unstimulated saliva, increases with flow rate • Pushes pH of stimulated saliva up to 8 • pH 5.6 critical for dissolution of enamel • Defence against acids produced by cariogenic bacteria • Derived actively from CO2 by carbonic anhydrase

34. Other ions • Fluoride • Low concentration, similar to plasma • Thiocyanate • Antibacterial (oxidated to hypothiocyanite OSCN- by active oxygen produced from bacterial peroxides by lactoperoxidase) • Higher conc. => lower incidence of caries • Smokers - increased conc. • Sodium, potassium, chloride • Lead, cadmium, copper • May reflect systemic concentrations - diagnostics

35. Organic components Saliva composition

36. Organic components of saliva • Mucins • Proline-rich proteins • Amylase • Lipase • Peroxidase • Lysozyme • Lactoferrin • Secretory IgA • Histatins • Statherin • Blood group substances, sugars, steroid hormones, amino acids, ammonia, urea

37. Mucins • Products of acinar cells from submandibular,sublingual and some minor salivary glands. • Asymmetrical molecule with open, randomly organized structure • Glycoproteins - protein core with many oligosaccharide side chains attached by glycosidic bond • Hydrophillic • Unique rheological properties (e.g., high elasticity, adhesiveness, and low solubility)

38. Major salivary mucins are: • MG1-adsorbs tightly to the tooth surface contributing to the enamel pellicle formation, thereby protecting the tooth surface from chemical & physical attack including acidic challenges • MG2-also binds to the tooth surface but is easily displaced, however it promotes clearance of oral bacteria by aggregation

39. Mucin Functions • Tissue Coating • Protective coating about hard and soft tissues • Primary role in formation of acquired pellicle • Concentrates anti-microbial molecules at mucosal interface • Lubrication • Align themselves with direction of flow (characteristic of asymmetric molecules) • Increases lubricating qualities (film strength) • Film strength determines how effectively opposed moving surfaces are kept apart

40. Aggregation of bacterial cells • Bacteria adhere to mucins-result in surface attachment, or • Mucin-coated bacteria may be unable to attach to surface • Bacterial adhesion • Mucin oligosaccharides mimic those on mucosal cell surface • React with bacterial adhesins, thereby blocking them

41. Amylases • Produced by acinar cells of major salivary glands • Metabolizes starch and other polysaccharides into glucose & maltose • Calcium metalloenzyme • Parotid; 30% of total protein in parotid saliva • “Appears” to have digestive function - inactivated in stomach, provides disaccharides for acid-producing bacteria • It is also present in tears, serum, bronchial, and male and female urogenital secretions • A role in modulating bacterial adherence

42. Lingual Lipase • Secreted by sublingual gland and parotid gland • Involved in first phase of fat digestion • Hydrolyzes medium to long chain triglycerides • Important in digestion of milk fat in newborn • Unlike other mammalian lipases, it is highly hydrophobic and readily enters fat globules

43. Statherins • Produced by acinar cells in salivary glands • Acidic peptide containing relatively high levels of proline,tyrosine and phosphoserine • Inhibits spontaneous precipitation of calcium phosphate salts from supersaturated saliva & favours remineralization • Calcium phosphate salts of dental enamel are soluble under typical conditions of pH and ionic strength

44. Supersaturation of calcium phosphates maintain enamel integrity • Also an effective lubricant for the tooth surface thus protecting it from physical forces

45. Proline-rich Proteins (PRPs) • Like statherin, PRPs are also highly asymmetrical • Present in the initially formed enamel pellicle and in “mature” pellicles • 2 types: • Basic • Acidic • Both are secretory products of major salivary glands • Acidic proline-rich protein binds tightly to hydroxyapatite and prevents precipitation of calcium phosphate and thereby protecting the enamel surface & preventing demineralization • Also bind to oral bacteria including mutans streptococcci

46. Role of PRPs in enamel pellicle formation • Acquired enamel pellicle is 0.1-1.0 µm thick layer of macromolecular material on the dental mineral surface • Pellicle is formed by selective adsorption of hydroxyapatite-reactive salivary proteins, serum proteins and microbial products such as glucans and glucosyl-transferase • Pellicle acts as a diffusion barrier, slowing both attacks by bacterial acids and loss of dissolved calcium and phosphate ions

47. Remineralization of enamel and calcium phosphate inhibitors • Early caries are repaired despite presence of mineralization inhibitors in saliva • Sound surface layer of early carious lesion forms impermeable barrier to diffusion of high mol.wt. inhibitors. • Still permeable to calcium and phosphate ions • Inhibitors may encourage mineralization by preventing crystal growth on the surface of lesion by keeping pores open

48. Calculus formation and calcium phosphate inhibitors • Calculus forms in plaque despite inhibitory action of statherin and PRPs in saliva • May be due to failure to diffuse into calcifying plaque • Proteolytic enzymes of oral bacteria or lysed leukocytes may destroy inhibitory proteins • Plaque bacteria may produce their own inhibitors

49. Interaction of oral bacteria with PRPs and other pellicle proteins • Several salivary proteins appear to be involved in preventing or promoting bacterial adhesion to oral soft and hard tissues • PRPs are strong promoters of bacterial adhesion • Amino terminal: control calcium phosphate chemistry • Carboxy terminal: interaction with oral bacteria • Interactions are highly specific

50. Lactoferrin • Iron-binding protein • Prevents iron from being used by microorganism that require it for metabolism • Nutritional immunity (iron starvation) • Some microorganisms (e.g., E. coli) have adapted to this mechanism by producing enterochelins. • bind iron more effectively than lactoferrin • iron-rich enterochelins are then reabsorbed by bacteria • Lactoferrin, with or without iron, can be degraded by some bacterial proteases.