1. Sorry, story will be continued later, now listen to the GIT Lecture. - Francis Stanley.

2. 1.Digestive system activity 1.Ingestion - 2.Propulsion 3.Mechanical digestion 4.Chemical digestion 5.Absorption 6.Defecation

3. Lecture:5 [Phy] Saliva Objectives The objective of the lecture is to discuss the synthesis, secretion, composition, functions, regulation of salivation and consequences of deficiency in salivation

4. At the end of the lecture, students should be able to: 1.Describe the composition of saliva 2.Discuss the mechanism for secretion of saliva 3.Explain the functions of each constituent of the saliva 4.Describe how salivation is regulated.

5. 1. Introduction: “Saliva in the mouth is the mixed product of 3 pairs of major salivary glands, the parotid, submandibular and sublingual glands as well as numerous ‘minor’ salivary glands found in the submucosa under most soft tissue surfaces in the mouth

6. 2. Reflex salivary secretion: “Salivary gland secretion is a nerve mediated reflex and once the autonomic nerve supply, particularly the parasympathetic nerve, has been interrupted then secretion from most glands ceases almost entirely. There are a few salivary glands that maintain a ‘spontaneous’ secretion in the absence of nerve mediated stimuli but even in these glands a normal rate of secretion requires an intact autonomic nerve supply.

7. composition of saliva : (Saliva is hypotonic - 99.5% water Remaining 0.5%) 1.Ions: K +, Na +, Ca 2+, Mg 2+, H + Cl -, HCO 3 - 2.Small organic molecules Urea, hormones, lipids, DNA, RNA

8. Saliva Water 99.5% Solid (0.5%) Solids ( Organic & Inorganic) Organic -0.3 % Ptyalin Kalikerin Lysozyme Carbonis anhydrase Blood group substances Nerve Growth Factor (NGF) Mucin Antibodies Ig A)

9. Inorganic; (0.2%) Cations Sodium Potassium Calcium Megnesium Anions: Chloride Bicarbonate Phosphate Thiocyanate.

10. Mechanism of salivary secretion:

11. A.) Parasympathetic stimulation 1) Is mediated mainly by acetylcholine in combination with NANC peptides (e.g. VIP) 2) Evokes most of the salivary fluid secreted. Mainly acts through M3 and to a lesser extent M1 muscarinic cholinergic receptors 3) Causes variable degrees of exocytosis from salivary cells but is responsible for most mucin secretion by mucous glands 4) Induces contraction of myoepithelial cells 5) Increases glandular blood flow as part of the salivary reflex. Effects of autonomic nerves on salivary gland function :

12. Sympathetic stimulation: 1) Is mediated mainly by noradrenaline and acts essentially on cells receiving parasympathetic impulses, which tends to produce synergistic effects, but exerts little effect on mucous gland secretion. 2) Often does not cause much mobilization of fluid but DOES NOT inhibit salivary secretion. 3) Tends to modulate the composition of saliva by increasing exocytosis from salivary cells. 4) Induces contraction of myoepithelial cells. 5) Exerts control on glandular blood flow but NOT as part of the salivary reflex.

13. Salivary functions:Salivary Multy –funcions: 8. Anti- Bacterial 1.Buffering 2.Digestion 3.Mineral-ization 4.Lubricat- ion &Visco- elasticity 5.TissueCoating 6.Anti-Fungal 7.Anti-Viral Carbonic anhydrases, Amylases, Mucins, Lipase Cystatins,Proline- rich proteins, Statherins Mucins Amylases, Cystatins, Mucins, Proline-rich proteins Histatins Cystatins,Mucins Amylases, Cystatins, Histatins, Mucins, Peroxidases adapted from M.J. Levine, 1993

14. Protective functions of saliva Mechanical cleansing (water/flow) Lubrication of tissues and teeth (secreted proteins) Buffering of acids (HCO 3 -, HPO 4 2-, peptides) Maintaining tooth integrity Post-eruptive maturation (Ca 2+, F -, HPO 4 2- ) Mineralization equilibrium (Ca 2+, F -, HPO 4 2- ) Pellicle (proteome components) Maintaining tissue integrity (proteome components) Regulation of the oral flora (proteome components)

15. Saliva and oral functions Food processing (water) Taste solute Bolus formation and swallowing (secreted proteins) Digestion (secreted proteins) Speech (water, secreted proteins) Lubrication and rehydration Excretion (the long way around) Small molecules (nitrate, thiocyanate. etc.) May interact with salivary proteins, oral bacteria

16. Saliva composition……………………….. Saliva from different glands differs in composition Parotid - dominated by serous secretory cells SM/SL minor - mixed serous or mostly mucous Qualitative and quantitative differences in output Composition is affected by level of gland activity Spontaneous (baseline) activity (during sleep) Unstimulated/”resting” (awake, but mouth at rest) Stimulated (eating or talking) Qualitative and quantitative differences in output

17. Mucin Functions Tissue Coating Protective coating about hard and soft tissues Concentrates anti-microbial molecules at mucosal interface Lubrication Align themselves with direction of flow Increases lubrication

18. Mucin Functions………… Aggregation of bacterial cells Mucin-coated bacteria may be unable to attach to surface Bacterial adhesion React with bacterial adhesins, thereby blocking them

19. Amylases Hydrolyzes  (1-4) bonds of starches such as amylose and amylopectin.

20. Lingual Lipase Secreted by von Ebner’s glands of tongue Involved in first phase of fat digestion Hydrolyzes medium- to long-chain triglycerides Important in digestion of milk fat in new-born Unlike other mammalian lipases, it is highly hydrophobic and readily enters fat globules

21. Statherins Calcium phosphate salts of dental enamel are soluble Supersaturation of calcium phosphates maintain enamel integrity Statherins prevent precipitation or crystallization of supersaturated calcium phosphate in ductal saliva and oral fluid

22. Proline-rich Proteins (PRPs)  Inhibit calcium phosphate crystal growth  Present in the initially formed enamel pellicle and in “mature” pellicles.

23. Calculus formation 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

24. Anti-microbial activities of saliva

25. Lysozyme (LZ) Oral LZ is derived from at least four sources major and minor salivary glands, phagocytic cells and gingival crevicular fluid (GCF) Biological function: Classic concept of anti-microbial activity of LZ is based on its muramidase activity (hydrolysis of  (1-4) bond between N- acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer.

26. Histatins A group of small histidine-rich proteins Potent inhibitors of Candida albicans growth

27. Cystatins Are inhibitors of cysteine-proteases Considered to be protective against unwanted proteolysis bacterial proteases lysed leukocytes May play inhibit proteases in periodontal tissues Also have an effect on calcium phosphate precipitation

28. Salivary peroxidase systems Sialoperoxidase (SP, salivary peroxidase) Produced in acinar cells of parotid glands Also present in submandibular saliva Readily adsorbed to various surfaces of mouth enamel, salivary sediment, bacteria, dental plaque

29. Components of the peroxidase anti-microbial system oral bacteria (facultative aerobes/catalase negative) produce large amounts of peroxide Thiocyanate ion (SCN - ) which is converted to hypothiocyanite ion (OSCN - ) by peroxidase salivary concentration is related to diet and smoking habits

30. Thiocyanate reactions The pK for HOSCN/OSCN - is 5.3 More acid favors HOSCN Due to uncharged nature, HOSCN penetrates bacterial cell envelope better H 2 O 2 + SCN - OSCN - +H 2 O SP and/or MP HOSCN OSCN - + H+ Hypothiocianous acid Hypothiocyanite ion Acid/Base Equilib.

31. Innervation of stimulation Dual autonomic innervation of salivary glands Parasympathetic - secretion of water and ions Sympathetic - protein secretion Both act simultaneously and synergistically Mediated by G-protein coupled receptors Parasympathetic - M3 muscarinic receptors Minor players - neuropeptide; nucleotide receptors VIP, Substance P, nucleotides, etc. Sympathetic -  2 adrenergic receptors Minor players -  adrenergic receptors Two different signal transduction pathways

32. MECHANISM OF SALIVARY SECRETION (NURAL- AUTONOMIC ; Parasympathetic & Sympathetic)

33. Muscarinic messages http://www.liv.ac.uk/~petesmif/teaching/1bds_mb/p4/15.gif The Phospholipase C - IP 3 pathway sends the message Intracellular (and extracellular) Ca 2+ flux is a major effector Parasympathetic Mechanism of salivary secretion:

34. Sympathetic Mechanism of salivary secretion: http://www.liv.ac.uk/~petesmif/teaching/1bds_mb/p4/16.gif The adenylate cyclase - cAMP pathway sends the message Effectors are activated by a phophorylation cascade (Noradrenaline) Adrenergic messages:

35. Water/electrolyte secretion Water secretion is driven by osmotic changes Mediated by ionic fluxes From basolateral surfaces to the apex (lumen) Involves ion pumps and channels Basolateral Na + -K + -ATPase Ca 2+ activated K + channel Na + -K + -2Cl - -cotransporter (NKCCl) Na + -H + exchanger Cl - - HCO 3 - exchanger, plus Carbonic anhydrase Lumenal Ca 2+ activated Cl - channel HCO 3 - channel (Ca 2+ activated?), plus Carbonic anhydrase

36. Alternative mechanisms Na + -K + -ATPase Ca 2+ activated K + channel Na + -K + -2Cl - -cotransporter Ca 2+ activated Cl - channel Na + -H + exchanger Cl - - HCO 3 - exchanger Carbonic anhydrase Na + -H + exchanger HCO 3 - channel Carbonic anhydrase Adapted from Turner and Sugiya, Oral Dis. 2:3-11, 2002

37. Regulation of Salivary secretion: Important studies suggest that preassure generted by salivary secrction is dependent on blood preassure. Parasympathetic stimulation of salivary glands causes a higher blood flow. The current secretion model predicts that, when stimulated, salivary acinar cells lose KCl. The loss of K+ and Cl-, across basolateral and apical membranes, respectively, creates a large transepithelial potential difference. This lumen-negative potential difference drives Na+ flux between acinar cells into the lumen, and H2O follows the resulting NaCl osmotic gradient.

38. Sustained secretion is dependent on the activation of K+ and Cl- reuptake mechanisms located in the basolateral membranes. The net effect of simultaneously activating Cl- efflux and Cl- reuptake mechanisms is transepithelial Cl- movement, the driving force for fluid secretion. It is interesting to note that little desensitization occurs, i.e., in the continuous presence of a muscarinic agonist, salivary glands can secrete for hours.

39. Sample Question…………………………………………………………… … Describe the composition and functions of saliva, and explain how salivation is regulated. LAQ: ( 10 Marks )