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Introduced by: Dr/Abousree El-Lethy

الرحيم الرحمن الله بسم

•Vitamins K and C

Block: Head & Neck Structure and FunctionBiochemistry

Lecture: Biochemistry of Saliva

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Saliva is produced in and secreted from acinar cells in salivary glands.

Major glands of secretions are parotid submandibular, and sublingual.

Daily secretion = 800-1500 mL PH = 6-7

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Functions of Saliva

Moistening food

Beginning of digestion

Adjust salt appetite

Containing factors that inhibit adhesion and destroy bacteria.

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Outline of multifunctions of salivary secreations

SalivarySecretions

(3) Anti-

Bacterial(4) Buffering

(5) Digestion

(6) Mineral-ization

(7) Lubricat-ion &Visco-

elasticity

(8) TissueCoating

(1) Anti-Fungal

(2) Anti-Viral

Carbonic anhydrases,Histatins

Amylases,

Mucins, Lipase

Cystatins,Histatins, Proline-

rich proteins,Statherins

Mucins, StatherinsAmylases,

Cystatins, Mucins, Proline-rich proteins, Statherins

Histatins

Cystatins,Mucins

Amylases, Cystatins,Histatins, Mucins,

Peroxidases

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Composition of Saliva

1-Aqueous fluids H2O, α-amylase, lingual lipase, IgA, kallikrein, muramidase (lyses muramic

acid of Staphylococcus) & lactoferrin.

2-Electrolytes or inorganics Ca, Ph, F, K, Na & Cl

HCO3 defense enemal against acids (pH5.6) produced by cariogenic bacteria

During hypotonic Saliva (low flow rate):o High and HCO3 (Pushes pH of stimulated saliva up to 8)

o Low Na and CI−

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3-Mucus secretion proteins

Mucin

Statherins

Proline-rich Proteins

Anti-microbial proteins

1)Lactoferrin

2)Histatins

3)Lysozyme

4)Cystatins

5)Salivary peroxidase

6)Secretory Immunoglobulins

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1) α-amylase, parotid glands It cleaves α -1 ,4-glycosidic bonds of starches such as

amylose and amylopectinMaltose is the major end-product (20% is glucose)

Optimum pH is 7 and inactivated at pH 4 but continues to work for sometime in unmixed food in oral portion of

stomach

2) Lingual lipase (hydrophobic)It is secreted by von Ebner’s glands of tongue and

hydrolyzes lipids It continues working into duodenum

Enzymes

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(1) Mucins

Asymmetrical molecules of globular proteins with polypeptide

backbone (apomucin) and side-chain of negatively charged

groups (e.g. sialic acid and bound sulfate).

Hydrophillic (resists dehydration, high elasticity, adhesiveness,

and low solubility)

Two major mucins (MG1 and MG2)

Mucus secretion proteins

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Mucin Functions

Lubrication &Visco-elasticity

Tissue coating (protection)

Aggregation of bacterial cells

– Bacterial adhere to mucins may 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

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(2) Statherins

Statherins prevent precipitation or crystallization of supersaturated calcium phosphate in ductal saliva and oral fluid

Lubrication and viscosity

(3) Proline-rich Proteins 40% of amino acids is proline, Subdivided into three groups

(acidic, basic, glycosylated) Inhibitors of calcium phosphate crystal growth

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(5) Anti-microbial proteins

1- Lactoferrin

Iron-binding protein

Some microorganisms (e.g., E. coli) have adapted to this mechanism by

producing enterochelins.

2-Histatins

A group of small histidine-rich proteins

Protent inhibitors of Candida albicans growth

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3- Lysozyme (muramidase )

Present in numerous organs and most body fluids

hydrolysis of (1-4) bond between N-acetylmuramic acid and N-

acetylglucosamine in the peptidoglycan layer of bacteria.

– Gram negative bacteria generally more resistant than gram positive

because of outer lipid phosphate layer.

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4- Cystatins

Are inhibitors of cysteine-proteases

Considered to be protective against unwanted proteolysis

– bacterial proteases

– lysed leukocytes

They inhibit proteases in periodontal tissues

They affect on calcium phosphate precipitation

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5- Salivary peroxidases

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

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6- Secretory Immunoglobulins

Immunoglobulin A (IgA) is an antibody secreted by mucosal linings in

mucous secretions.

IgA has two subclasses (IgA1 and IgA2) and can exist in a dimeric form

called secretory IgA (sIgA).

The secretory component of sIgA protects the immunoglobulin from the

being degraded by proteolytic enzymes

It plays a critical role in mucosal immunity.