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Saliva – Physiology, Composition, Functions & Forensic Applications

Mission, Vision & Core Values

  • Mission: CHRIST aims to be a nurturing ground for an individual’s holistic development so they can contribute effectively to society within a dynamic environment.

  • Vision: Excellence and Service.

  • Core Values:

    • Faith in God

    • Moral Uprightness

    • Love of Fellow Beings

    • Social Responsibility

    • Pursuit of Excellence

  • Presenter: Dr. V. Krishnakumar, Ph.D. – Assistant Professor of Zoology, Department of Life Sciences

Saliva – General Overview

  • Complex biological fluid secreted by acinar cells of major and minor salivary glands.

  • Serves as an indicator of various plasma constituents; hence, used for clinical and forensic diagnostics.

  • Predominantly water, yet contains numerous molecules essential for digestion, oral health, immunity and wound repair.

Daily Production & Sources

  • Volume: 1.0 - 1.5\,\text{L} per day in healthy adults.

  • Glandular contribution:

    • Submandibular ≈ 70\%

    • Parotid ≈ 25\%

    • Sublingual ≈ 5\%

  • Production markedly increases during mastication (eating).

Major Physiological Functions

  • Maintains oral moisture & comfort.

  • Facilitates chewing, tasting and swallowing.

  • Provides antibacterial, antifungal, antiviral protection; prevents halitosis.

  • Supplies proteins & minerals that strengthen enamel, preventing caries & periodontal disease.

  • Assists in food digestion (carbohydrates & lipids).

  • Acts as a bicarbonate/phosphate buffer — neutralises acids.

  • Enables coating & lubrication of oral tissues and prostheses (e.g.
    dentures).

  • Promotes wound healing via growth factors and protective peptides.

Functional Molecule Map

Functional Domain

Key Molecules

Antibacterial

Histatin 5, \beta-defensins, cathelicidins

Antifungal

Histatins

Antiviral

Mucins

Wound healing / Growth factors

Histatins, secretory leucocyte protease inhibitor, trefoil factor, leptin, cystatins

Buffering

Bicarbonate, phosphate, proteins

Coating & lubrication

Mucins, proline-rich proteins, statherins, cystatins

Digestion

Amylase, lipase, mucins

Teeth mineralisation

Statherins, proline-rich proteins, histatins, cystatins

(Note: Table reproduced from transcript slide content.)

Anatomy of Salivary Glands

  • Parotid glands

    • Location: just anterior to each ear.

    • Two lobes: superficial & deep.

    • Saliva exits via ducts opening near upper molars.

  • Submandibular glands

    • Location: beneath the mandible.

    • Two parts: superficial lobe & deep lobe.

    • Ducts open under the tongue.

  • Sublingual glands

    • Location: beneath either side of the tongue (floor of the mouth).

    • Multiple small ducts directly enter the oral cavity under the tongue.

Detailed Composition of Whole Saliva

  • Water: 99.5\%

  • Solids: 0.5\%

    1. Inorganic ions

    • \text{Na}^+, \text{K}^+, \text{Ca}^{2+}

    • \text{HCO}_3^-, phosphate, chloride, bromide, fluoride

    1. Organic molecules

    • Enzymes:

      • \alpha-Amylase (ptyalin)

      • Maltase

      • Lingual lipase

      • Lysozyme

      • Phosphatase

      • Carbonic anhydrase

      • Kallikrein

    • Glycoproteins / Proteins:

      • Mucins

      • Albumin

      • Proline-rich proteins

      • Statherins

      • Cystatins

      • Histatins

      • Immunoglobulin A (IgA)

      • Lactoferrin

      • Blood-group antigens (ABO)

    • Low-molecular weight compounds: free amino acids, urea, uric acid, creatinine, xanthine, hypoxanthine

    1. Gases: \text{O}2, \text{CO}2, \text{N}_2

  • Glucose: normally absent; appears in conditions such as diabetes mellitus.

Key Enzymes & Physico-Chemical Properties

  • \alpha-Amylase (ptyalin)

    • Initiates starch digestion; optimum pH = 7.4 (oral pH).

  • Lingual lipase

    • Optimum pH \approx 4.0; becomes active when saliva mixes with gastric juice in the stomach.

  • Kallikrein

    • Cleaves high-molecular-weight kininogen to produce bradykinin – a potent vasodilator.

  • Antimicrobial enzymes: Lysozyme, lactoferrin, phosphatase.

  • Opiorphin: newly discovered salivary peptide exhibiting analgesic (pain-killing) properties.

Neural Control (Reflex Pathway)

  • Afferent stimuli: thought, sight, smell (cranial nerves VII & IX), and taste (cranial nerve IX).

  • Central processing: dorsal horn of brainstem.

  • Efferent pathways:

    • Parasympathetic fibres via submandibular ganglion (to submandibular/sublingual glands).

    • Parasympathetic fibres via otic ganglion (to parotid gland).

    • Sympathetic fibres via cervical ganglion (modulate volume & composition).

Forensic Importance of Saliva

  • Increasingly utilised as diagnostic & forensic evidence owing to:

    • Ease of collection (present on skin, envelopes, cigarette butts, bottles, metal cans, chewing gum, tobacco spit, etc.).

    • Stability of DNA, proteins & antibodies within dried stains.

    • Ability to provide personal contact information linking victim & perpetrator.

  • Blood-group & secretor status

    • Secretors: individuals whose saliva/body fluids express ABO antigens (~80\% of population).

    • Enables determination of blood type from saliva.

  • DNA profiling

    • Buccal epithelial cells in saliva allow generation of STR or other genetic profiles.

Collection & Preservation Guidelines

  • Dried stains: moisten with sterile water, swab with cotton, air-dry, package in clean tube/bag (avoid contamination).

  • Moist samples (gum, spit, etc.): seal as-is in airtight container.

  • Note contamination sources (lipstick, blood) during collection.

Presumptive & Confirmatory Tests

  1. Amylase-based Assays

    • Principle: saliva has high \alpha-amylase activity.

    • Two broad categories:
      a. Enzymatic activity assays – measure total amylase; cannot distinguish human salivary amylase (HSA) from human pancreatic (HPA) or non-human sources.
      b. Target-specific assays – detect HSA proteins or AMY1 RNA; provide higher confirmatory value.

  2. Starch–Iodine Test (classical presumptive assay)

    • Chemistry: iodine forms dark blue complex with amylose; amylase digests starch → colour loss.

    • Reagents: 0.5\% soluble starch (e.g., 50\,\text{mg} / 10\,\text{mL H}_2O) and Lugol’s iodine solution.

  3. Phadebas® Test

    • Commercial colorimetric tablet containing starch bound to an insoluble blue dye; amylase cleavage releases dye → blue halo.

  4. Immunochromatographic kits

    • Monoclonal antibodies specific to HSA (e.g., Rapid Stain Identification Series – Saliva (RSID)).

    • Positive colour change confirms human salivary origin.

  5. Alternate Light Source (ALS) Visualisation

    • Excitation ≈ 470\,\text{nm}; observe fluorescence while wearing orange filters.

    • Less intense than semen stains; still aids in locating deposits.

  6. Microscopic Examination

    • Histological staining can reveal buccal epithelial cells → presence of saliva.

Workflow for Forensic Identification of Saliva Stains

  1. Search/Locate → ALS (470 nm) & visual inspection.

  2. Presumptive Testing → starch–iodine or Phadebas.

  3. Confirmatory Testing → RSID-Saliva or equivalent human-specific immunoassay / RNA-based test.

  4. DNA Extraction & Profiling (if sample quality allows).

Ethical & Practical Implications

  • Non-invasive sampling (e.g.
    saliva swab) offers alternative to blood draws; valuable for public health screening and personalised medicine.

  • Must ensure chain-of-custody and contamination control in forensic handling.

  • Recognition that secretor status can influence evidence interpretation (e.g.
    ABO not present in non-secretors).

  • Awareness of potential privacy concerns when extracting genomic data from saliva traces found in public settings.

Quick-Reference Equations & Stats

  • Daily flow: Q_{saliva} \approx 1.0 - 1.5\,\text{L day}^{-1}

  • Gland contributions: Q{submandibular} = 0.70Q, Q{parotid} = 0.25Q, Q_{sublingual} = 0.05Q

  • Optimal pH ranges: pH{amylase} \approx 7.4, pH{lingual\,lipase} \approx 4.0

  • Secretor prevalence: \sim 80\% of general population.

Study Tips & Concept Connections

  • Relate buffering role of saliva to acid–base chemistry covered in biochemistry courses.

  • Compare innate immune molecules (lysozyme, defensins) with systemic immunity topics.

  • Link bradykinin production (via kallikrein) to vasoactive peptide discussions in physiology.

  • Remember forensic ALS technique parallels semen & blood stain searches – similar luminology/fluorescence principles.

  • Use the enzyme-substrate nucleotide concept (starch–iodine) to reinforce enzyme assay logic for practical lab exams.

Potential Exam Questions (Self-Practice)

  • Describe the mechanism by which saliva prevents tooth decay.

  • Explain why lingual lipase remains inactive in the oral cavity but becomes active in the stomach.

  • Outline the steps and reagents of the starch–iodine test for saliva detection.

  • Discuss the forensic significance of secretor status.

  • Compare enzymatic versus immunological methods of saliva identification.

End of Notes