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  1. 1. Introduced by: Dr/Abousree El-Lethy بسم الله الرحمن الرحيم <ul><li>Vitamins K and C </li></ul>Block: Head & Neck Structure and Function Biochemistry Lecture: Biochemistry of Saliva
  2. 2. <ul><li>Saliva is produced in and secreted from acinar cells in salivary glands. Major glands of secretions are parotid submandibular, and sublingual. </li></ul><ul><li>Daily secretion = 800-1500 mL PH = 6-7 </li></ul>
  3. 3. Functions of Saliva <ul><li>Moistening food </li></ul><ul><li>Beginning of digestion </li></ul><ul><li>Adjust salt appetite </li></ul><ul><li>Containing factors that inhibit adhesion and destroy bacteria. </li></ul>
  4. 4. Outline of multifunctions of salivary secreations Salivary Secretions (3) Anti- Bacterial (4) Buffering (5) Digestion (6) Mineral- ization (7) Lubricat- ion &Visco- elasticity (8) Tissue Coating (1) Anti- Fungal (2) Anti- Viral Carbonic anhydrases, Histatins Amylases, Mucins, Lipase Cystatins, Histatins, Proline- rich proteins, Statherins Mucins, Statherins Amylases, Cystatins, Mucins, Proline-rich proteins, Statherins Histatins Cystatins, Mucins Amylases, Cystatins, Histatins, Mucins, Peroxidases
  5. 5. Composition of Saliva <ul><li>1-Aqueous fluids </li></ul><ul><li>H2O, α -amylase , lingual lipase , IgA, kallikrein, muramidase (lyses muramic acid of Staphylococcus) & lactoferrin. </li></ul><ul><li>2-Electrolytes or inorganics </li></ul><ul><li>Ca, Ph, F, K, Na & Cl </li></ul><ul><li>HCO 3 defense enemal against acids (pH5.6) produced by cariogenic bacteria </li></ul><ul><li>During hypotonic Saliva (low flow rate): </li></ul><ul><li>High and HCO3 ( Pushes pH of stimulated saliva up to 8 ) </li></ul><ul><li>Low Na and CI− </li></ul>
  6. 6. <ul><li>3-Mucus secretion proteins </li></ul><ul><li>Mucin </li></ul><ul><li>Statherins </li></ul><ul><li>Proline-rich Proteins </li></ul><ul><li>Anti-microbial proteins </li></ul><ul><li>Lactoferrin </li></ul><ul><li>Histatins </li></ul><ul><li>Lysozyme </li></ul><ul><li>Cystatins </li></ul><ul><li>Salivary peroxidase </li></ul><ul><li>Secretory Immunoglobulins </li></ul>
  7. 7. <ul><li>1) α -amylase, parotid glands </li></ul><ul><li>It cleaves α -1 ,4-glycosidic bonds of starches such as amylose and amylopectin </li></ul><ul><li>Maltose is the major end-product (20% is glucose) </li></ul><ul><li>Optimum pH is 7 and inactivated at pH 4 but continues to work for sometime in unmixed food in oral portion of stomach </li></ul><ul><li>2) Lingual lipase ( hydrophobic ) </li></ul><ul><li>It is secreted by von Ebner’s glands of tongue and hydrolyzes lipids </li></ul><ul><li>It continues working into duodenum </li></ul>Enzymes
  8. 8. <ul><li>(1) Mucins </li></ul><ul><li>Asymmetrical molecules of globular proteins with polypeptide backbone (apomucin) and side-chain of negatively charged groups (e.g. sialic acid and bound sulfate). </li></ul><ul><li>Hydrophillic (resists dehydration, high elasticity, adhesiveness, and low solubility) </li></ul><ul><li>Two major mucins (MG1 and MG2) </li></ul>Mucus secretion proteins
  9. 9. Mucin Functions <ul><li>Lubrication &Visco-elasticity </li></ul><ul><li>Tissue coating (protection) </li></ul><ul><li>Aggregation of bacterial cells </li></ul><ul><ul><li>Bacterial adhere to mucins may result in surface attachment, or </li></ul></ul><ul><ul><li>Mucin-coated bacteria may be unable to attach to surface </li></ul></ul><ul><li>Bacterial adhesion </li></ul><ul><ul><li>Mucin oligosaccharides mimic those on mucosal cell surface </li></ul></ul><ul><ul><li>React with bacterial adhesins, thereby blocking them </li></ul></ul>
  10. 10. <ul><li>(2) Statherins </li></ul><ul><li>Statherins prevent precipitation or crystallization of supersaturated calcium phosphate in ductal saliva and oral fluid </li></ul><ul><li>Lubrication and viscosity </li></ul><ul><li>(3) Proline-rich Proteins </li></ul><ul><li>40% of amino acid s is proline , Subdivided into three groups (acidic, basic, glycosylated) </li></ul><ul><li>Inhibitors of calcium phosphate crystal growth </li></ul>
  11. 11. <ul><li>(5) Anti-microbial proteins </li></ul><ul><li>1- Lactoferrin </li></ul><ul><li>Iron-binding protein </li></ul><ul><li>Some microorganisms (e.g., E. coli ) have adapted to this mechanism by producing enterochelins . </li></ul><ul><li>2-Histatins </li></ul><ul><li>A group of small histidine-rich proteins </li></ul><ul><li>Protent inhibitors of Candida albicans growth </li></ul>
  12. 12. <ul><li>3- Lysozyme ( muramidase ) </li></ul><ul><li>Present in numerous organs and most body fluids </li></ul><ul><li>hydrolysis of  (1-4) bond between N-acetylmuramic acid and N-acetylglucosamine in the peptidoglycan layer of bacteria . </li></ul><ul><ul><li>Gram negative bacteria generally more resistant than gram positive because of outer lipid phosphate layer. </li></ul></ul>
  13. 13. <ul><li>4- Cystatins </li></ul><ul><li>Are inhibitors of cysteine-proteases </li></ul><ul><li>Considered to be protective against unwanted proteolysis </li></ul><ul><ul><li>bacterial proteases </li></ul></ul><ul><ul><li>lysed leukocytes </li></ul></ul><ul><li>They inhibit proteases in periodontal tissues </li></ul><ul><li>They affect on calcium phosphate precipitation </li></ul>
  14. 14. <ul><li>5- Salivary peroxidases </li></ul><ul><li>Sialoperoxidase (SP, salivary peroxidase) </li></ul><ul><ul><li>Produced in acinar cells of parotid glands </li></ul></ul><ul><ul><li>Also present in submandibular saliva </li></ul></ul><ul><ul><li>Readily adsorbed to various surfaces of mouth </li></ul></ul><ul><ul><ul><li>enamel, salivary sediment, bacteria, dental plaque </li></ul></ul></ul><ul><li>Myeloperoxidase (MP) </li></ul><ul><ul><li>From leukocytes entering via gingival crevice </li></ul></ul><ul><ul><li>15-20% of total peroxidase in whole saliva </li></ul></ul>
  15. 15. <ul><li>6- Secretory Immunoglobulins </li></ul><ul><li>Immunoglobulin A (IgA) is an antibody secreted by mucosal linings in mucous secretions. </li></ul><ul><li>IgA has two subclasses (IgA1 and IgA2) and can exist in a dimeric form called secretory IgA (sIgA). </li></ul><ul><li>The secretory component of sIgA protects the immunoglobulin from the being degraded by proteolytic enzymes </li></ul><ul><li>It plays a critical role in mucosal immunity. </li></ul>