Saliva

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File:The taking of a saliva sample.jpg

Taking a saliva sample for testing

Saliva (also referred to as spit , spittle or slobber) is the watery and usually frothy substance produced in the mouths of humans and most other animals in the process of salivation. Saliva is produced in and secreted from the salivary glands. Human saliva is composed of 98% water, while the other 2% consists of other compounds such as electrolytes, mucus, antibacterial compounds, and various enzymes. As part of the initial process of food digestion, the enzymes in the saliva break down some of the starch and fat in the food at the molecular level. Saliva also breaks down food caught in the teeth, protecting them from bacteria that cause decay. Furthermore, saliva lubricates and protects the teeth, the tongue, and the tender tissues inside the mouth. Saliva also plays an important role in tasting food by trapping thiols produced from odourless food compounds by anaerobic bacteria living in the mouth.

Various species have evolved special uses for saliva that go beyond predigestion. Some swifts use their gummy saliva to build their nests. Some Aerodramus swiftlet nests are made only from saliva and used to make bird's nest soup. Cobras, vipers, and certain other members of the venom clade hunt with venomous saliva injected by fangs. Some arthropods, such as spiders and caterpillars, create thread from salivary glands.

Contents

Produced in salivary glands, human saliva is 98% water, but it contains many important substances, including electrolytes, mucus, antibacterial compounds and various enzymes.

It is a fluid containing:

• Water
• Electrolytes:
  • 2-21 mmol/L sodium (lower than blood plasma)
  • 10-36 mmol/L potassium (higher than plasma)
  • 1.2-2.8 mmol/L calcium (similar to plasma)
  • 0.08-0.5 mmol/L magnesium
  • 5-40 mmol/L chloride (lower than plasma)
  • 25 mmol/L bicarbonate (higher than plasma)
  • 1.4-39 mmol/L phosphate
  • Iodine (mmol/L usually higher than plasma, but dependent variable according to dietary iodine intake)
• Mucus. Mucus in saliva mainly consists of mucopolysaccharides and glycoproteins;
• Antibacterial compounds (thiocyanate, hydrogen peroxide, and secretory immunoglobulin A)
• Epidermal growth factor or EGF
• Various enzymes. There are three major enzymes found in saliva.
  • α-amylase (EC3.2.1.1). Amylase starts the digestion of starch and lipase fat before the food is even swallowed. It has a pH optima of 7.4.
  • lingual lipase. Lingual lipase has a pH optimum ~4.0 so it is not activated until entering the acidic environment of the stomach.
  • Antimicrobial enzymes that kill bacteria.
    • Lysozyme
    • Salivary lactoperoxidase
    • Lactoferrin
    • Immunoglobulin A
  • Proline-rich proteins (function in enamel formation, Ca²⁺-binding, microbe killing and lubrication)
  • Minor enzymes include salivary acid phosphatases A+B, N-acetylmuramoyl-L-alanine amidase, NAD(P)H dehydrogenase (quinone), superoxide dismutase, glutathione transferase, class 3 aldehyde dehydrogenase, glucose-6-phosphate isomerase, and tissue kallikrein (function unknown).
• Cells: Possibly as much as 8 million human and 500 million bacterial cells per mL. The presence of bacterial products (small organic acids, amines, and thiols) causes saliva to sometimes exhibit foul odor.
• Opiorphin, a newly researched pain-killing substance found in human saliva.

Different reagents used to determine the content of saliva \1. Molisch test gives a positive result of purple color that is costituent to the presence of carbohydrates

References

• Venturi S, Venturi M. (2009). Iodine in evolution of salivary glands and in oral health. Nutrition and Health. 20 :119–134. PMID: 19835108
• Bahar, G., Feinmesser, R., Shpitzer, T., Popovtzer, A. and Nagler, R.M. (2007). Salivary analysis in oral cancer patients: DNA and protein oxidation, reactive nitrogen species, and antioxidant profile. Cancer, 109, 54–9.
• Banerjee, R.K., Bose, A.K., Chakraborty, T.K., de, S.K. and Datta, A.G. (1985). Peroxidase-catalysed iodotyrosine formation in dispersed cells of mouse extrathyroidal tissues. J Endocrinol. 2, 159–65.
• Banerjee, R.K. and datta, A.G. (1986). Salivary peroxidases. Mol Cell Biochem, 70, 21-9.
• Bartelstone, H. J. (1951). Radioiodine penetration through intact enamel with uptake by bloodstream and thyroid gland. J Dent Res. 5 :728–33.
• Bartelstone, H.J., Mandel, I.D., Oshry, E. and Seidlin, S.M. (1947). Use of radioactive iodine as a tracer in the Study of the Physiology of teeth. Science. 106, 132.