Saliva Notes

Saliva: A Vital Fluid

Salivary Gland Anatomy & Secretions

  • Major Glands:

    • Parotids (serous, watery)

    • Submandibular (mostly serous, moderately viscous)

    • Sublingual (mainly mucous, very viscous)

  • Minor Glands:

    • Mucous secretion, except lingual serous glands (von Ebner's glands)

    • Locations: lower lip, tongue, palate, cheeks, pharynx

    • Absent in: gingiva, anterior hard palate

Saliva Composition & Production

  • Composition: 99% water, 0.5% electrolytes & proteins

    • Electrolytes: Sodium, potassium, calcium, magnesium, bicarbonate & phosphates

    • Proteins: Ig, enzymes (amylase, lysozyme), mucins, urea & ammonia

  • Average flow: 0.5 - 1.5 L/day

  • Production: Two-stage process

    1. Primary saliva: Isotonic, produced in acini

    2. Secondary saliva: Hypotonic, modified in duct network, low in sodium, glucose, bicarbonate, urea

    3. Stimulated saliva: Hypertonic, increased Na levels

Factors Affecting Salivary Flow

  • Decreased flow:

    • Hypofunction (50% reduction)

    • Sleep (circadian rhythm)

    • Summer (circannual rhythm)

    • Reclined position, blindfolded, fasting

    • These decrease flow because they reduce the stimulation of salivary glands, leading to a lower production of saliva.

  • Increased flow:

    • Smoking, olfaction, vomiting

      • These cause increased flow because they stimulate the salivary glands through various mechanisms, such as the activation of taste receptors and increased nerve activity.

Control of Saliva Secretion

  • Salivary center in medulla

  • Triggers: Mechanical, gustatory, olfactory

  • Altered by pain, medication, disease

  • Parasympathetic NS stimulation: Constant low-level secretion

  • Sympathetic NS: increased protein (due to noradrenaline)

  • Parasympathetic NS: increased watery secretion (due to acetylcholine)

  • Nerve-mediated reflex, originating in salivary nuclei.

Saliva Functions & Components

  • Lubrication & protection

  • Buffering & clearance

  • Maintenance of tooth integrity

  • Antibacterial activity

  • Taste & digestion

  • Bicarbonates, phosphates & urea: pH modulation & buffering

  • Proteins & mucins: Cleanse, aggregate/attach oral microbes, contribute to dental plaque metabolism

  • Calcium, phosphate, proteins: Anti-solubility factor, modulate de- and re-mineralization

  • Immunoglobulins, proteins, enzymes: Antibacterial action

  • Growth factors: Wound healing

Proteins in Saliva

  • Proline-rich proteins: friction protection

  • Amylase: begins starch digestion

  • Lipase: lipid digestion

  • Mucus glycoprotein/proteoglycan: lubrication

  • Agglutinins: antigen aggregation

  • Cystatins: inhibit proteases

  • Histatins: antimicrobial/ antifungal/ antiviral

  • Statherin: enamel recal/prevent mineral accretions/ antimicrobial

  • Defensins: antibacterial/ antiviral

  • Lactoferrin: chelates iron

  • Growth factors EGF & VEGF: wound healing

  • Urea: raises pH

  • Lysozyme: damages microbe cell walls

Acquired Pellicle

  • Thin acellular film on surface epithelium and enamel

  • Protein/CHO/Lipids

  • Selectively binds salivary glycoproteins

  • Functions: Lubrication, remin/demin, influences early microbiome

Mucins (glycosylated protein)

  • Lubrication & Protection: Coating soft & hard tissues, barrier against irritants, carcinogens, chemicals, desiccation, diffusion barrier against acids, antibacterial, supports commensal bacteria

  • Complex protein molecules (glycoproteins) with low solubility, high viscosity/elasticity/adhesiveness

  • Adsorbs to tooth, contributes to pellicle, protects from acid, complexes with other proteins, binds to enamel, easily dislodged, aggregation & clearance of oral bacteria, predominates in caries-resistant patients

Buffering & Clearance

  • Most important functions for caries prevention

  • Bicarbonate (most important), phosphate, urea & amphoteric proteins neutralize acids

  • Clearance related to saliva flow rate; high flow rate = reduced caries risk

Maintenance of Tooth Integrity

  • Demineralization: Acids dissolve enamel crystals (pH 5-5.5)

  • Remineralization: Replacing lost minerals, supersaturation of salivary mineral, proteins bind to enamel surface, fluoride increases crystal precipitation