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Saliva

Saliva. Composition of Saliva. 97% to 99.5% water Minerals Electrolytes Buffers Enzymes (amylase, lysozyme, sialoperoxidase, lingual lipase, ribonuclease, deoxyribonuclease, kallikreins, and carbonic anhydrases) Enzyme inhibitors Growth factors. Composition of Saliva. Cytokines

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Saliva

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  1. Saliva

  2. Composition of Saliva • 97% to 99.5% water • Minerals • Electrolytes • Buffers • Enzymes (amylase, lysozyme, sialoperoxidase, lingual lipase, ribonuclease, deoxyribonuclease, kallikreins, and carbonic anhydrases) • Enzyme inhibitors • Growth factors

  3. Composition of Saliva • Cytokines • R proteins which binds cobalamines (B12) and keep them in absorbable form • Immunoglobulines (secretory immunoglobulin A, sIgA) • Mucin • Antimicrobial components (Histatins, Statherins, Proline-rich proteins, Lactoferrin) • Antibodies

  4. Functions Anti- Bacterial Buffering Anti- Viral Digestion Salivary Families Mineral- ization Anti- Fungal Lubricat- ion &Visco- elasticity Tissue Coating

  5. Salivary Proteins • Salivary proteins occurring in families, consisting of structurally closely related family members • Salivary protein biosynthesis starts with the transcription and translation of salivary protein genes in the glands • Post-translational processing involving protein glycosylation, phosphorylation and proteolysis • Once glandular secretions enter the non-sterile oral environment, proteins are subjected to additional and continuous protein modifications, leading to extensive proteolytic cleavage, partial deglycosylation, and protein-protein complex formation

  6. Mucins (mucus glycoproteins) • Mucins are extra-cellular large highly glycosylated molecules having mucin domains • Mucin domains are rich in the amino acids threonine, serine, and proline • Oligosaccharides are linked to the hydroxyl amino acids • Mucins are of two types; secreted and membrane bound • Secreted mucins are gel-forming due to their polymeric nature

  7. Mucins • The major mucin of the gastrointestinal tract is called MUC2 and is produced by the intestinal goblet cells • MUC2 can form insoluble mucus gels • MUC2 has two central mucin domains and cysteine-rich domains at both the N- and C- terminal ends • Addition of O-glycans starts in Golgi apparatus • MUC2 forming polymers in late Golgi apparatus

  8. 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 (characteristic of asymmetric molecules) • Increases lubricating qualities (film strength)

  9. Statherins: • Inhibit mineralization and so help to prevent precipitation of calcium and phosphate on intact tooth surface. • Prevent crystallization of supersaturated calcium phosphate in the salivary duct and oral fluid • Proline-rich Proteins (PRPs): • Coat the teeth with a thin layer (pellicle) that serves as a protective diffusion barrier on the tooth surface • Inhibit mineralization and so help to prevent precipitation of calcium and phosphate on intact tooth surface.

  10. Anti-microbial activities of saliva • Lactoferrin: • 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. • In unbound state, a direct bactericidal effect

  11. Anti-microbial activities of saliva • Lysozymes: • Present in numerous organs and most body fluids • Oral LZ is derived from at least four sources • 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 beta (1-4) bond between N-acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer. • Gram negative bacteria generally more resistant than gram positive

  12. Anti-microbial activities of saliva • Histatins: • A group of small histidine-rich proteins • Potent inhibitors of Candida albicans growth • Cystatins: • Are inhibitors of cysteine-proteases

  13. Anti-microbial activities of saliva • 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 • Myeloperoxidase (MP) • From leukocytes entering via gingival crevice • 15-20% of total peroxidase in whole saliva

  14. Components of the peroxidase anti-microbial system • Peroxidase enzymes (SP or MP) • Hydrogen peroxide (H2O2) • 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

  15. Thiocyanate reactions Hydrogen peroxide (bacterial activity) + thiocyanate (saliva) → → → → oxidation product (hypothiocyanate) toxic to bacteria

  16. HOSCN/OSCN--mediated cell damage • Can oxidize sulfhydryl groups of enzymes • Block glucose uptake • Inhibit amino acid transport • Damage inner membrane, leading to leakage of cells • Disrupt electrochemical gradients

  17. Amylases • Two types; pancreatic (P-type) and salivary (S-type). • Alpha-amylases are calciummetalloenzymes • Acts on alpha-1,4- glycosidic bonds • Full activity is displayed only in the presence of various anions, such as chloride, bromide, nitrate or cholate. • It is the only plasma enzyme normally found in urine

  18. Amylases • There are 12 distinct phenotypes for the salivary isoenzyme and 6 for the pancreatic isoenzyme. • Isoenzymes are products of two closely linked loci on chromosome 1 • Salivary amylase (ptyalin),is found in saliva and breaks starch down into maltose and dextrin • Salivary amylase is inactivated in the stomach by gastric acid • Pancreatic α-amylase randomly cleaves the α (1-4) glycosidic linkages of amylose to yield dextrin, maltose or maltotriose.

  19. Clinical significance of Amylases • Assays for amylase activity in serum and urine are largely of use for: • Investigation of pancreatic function • Diagnosis of diseases of the pancreas • Detecting the development of complications of pancreatic diseases • Diagnosis of salivary glands diseases and other nonpancreatic disorders. • Increased blood amylase levels in humans are found in: Salivary glands trauma, Mumps, Pancreatitis, Renal failure

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