Saliva

Numerous functions, new applications

With between 0.5 and 1.5 liters of this body fluid secreted per day, saliva clearly plays a critical, multifaceted role in human digestive, dental and immune health. Saliva is 99.5 percent water, with its relatively high viscosity a result of additional substances of many types, including:

  • Mucus – Consisting primarily of glycoproteins and mucopolysaccharides
  • Electrolytes – Including potassium, sodium, calcium, magnesium, chloride, bicarbonate, phosphate and iodine
  • Epidermal growth factor (EGF) – a small polypeptide responsible for cellular proliferation and differentiation; salivary EGF helps support oroesophageal and gastric tissue health, and provides some mucosal protection against endogenous acids as well as other chemical or bacterial agents
  • Antimicrobial enzymes and other compounds – Including hydrogen peroxide, thiocyanate, lysozyme, lactoferrin and immunoglobulin A
  • Proline-rich proteins – Supportive of tooth enamel formation, calcium ion binding and lubrication
  • Various digestive and other enzymes – Enzyme α-amylase initiates starch pre-digestion; lingual lipase is activated upon being swallowed and reaching the stomach; kallikrein helps produce bradykinin, a vasodilator
  • Opiorphin – An endogenous painkilling compound discovered in 2006

Saliva also contains a significant cellular component, with bacterial cells outnumbering human cells by a more than 60-to-1 ratio; each milliliter of saliva may contain 8 million human cells and as many as 500 million bacterial cells.

Genetics and identification

Because of the high number of human cells it contains, saliva has emerged this century as a highly reliable, easily collected source of genetic and other identifying material. DNA and serological substances isolated from cells in saliva can be readily sampled, prepared, analyzed and/or sequenced to reveal vast amounts of information about the person from whom the sample was collected. This has paved the way for advancements in multiple fields and industries, most notably:

  • Forensic sciences – Analysis of saliva has become a well-established tool for various applications, including:
    • Crime detection
    • Substance abuse detection
    • Hormone identification
    • Characterization of poisoning and animal bites
  • Genealogical research – DNA derived from white blood cells and buccal epithelial cells in the mouth via cheek swab can be obtained at high quality in relatively large quantities — as much per unit volume as a blood sample; private companies now regularly supply saliva collection kits for at-home sampling and subsequent ancestry analysis.

References

Iorgulescu, Gabriela. Saliva between Normal and Pathological. Important Factors in Determining and Oral Health. PubMed Central, National Center for Biotechnology Information. Available from URL: https://www.ncbi.nlm.nih.gov/pmc/.

Rabuka, Scott. 8 Facts Most People Don't Know about DNA from Saliva. DNA Genotek. Available from URL: https://blog.dnagenotek.com/.

Saliva. Encyclopedia Britannica. Available from URL: https://www.britannica.com/.

Saxena, Susmita and Kumar, Sanjeev. Saliva in Forensic Odontology: A Comprehensive Update. PubMed Central, National Center for Biotechnology Information. Available from URL: https://www.ncbi.nlm.nih.gov/pmc/.

Venturi, Sebastiano and Venturi, Mattia. Iodine in Evolution of Salivary Glands and in Oral Health. PubMed, National Center for Biotechnology Information. Available from URL: https://pubmed.ncbi.nlm.nih.gov/.

Additional Body Fluids

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