Saliva is the protein-rich hypotonic exocrine fluid produced and secreted into the oral cavity by the three paired major salivary glands: the parotid, submandibular, and sublingual glands. Saliva is also produced to a lesser extent by numerous minor glands located in the oral submucosal region. The tongue is particularly noted to contain 3 sets of minor salivary glands, namely the glands of Blandin and Nuhn, the glands of Weber, and the glands of Von Ebner.
The functional units of salivary glands consist of acini and ductal cells. Acini serve as secretory units, while the ductal epithelium modifies and transports the secretion from the acini into the oral cavity. The autonomic nervous system regulates salivary secretion. Generally, parasympathetic stimulation causes an increase in salivary flow, while sympathetic stimulation does the opposite. The aggregate of saliva secretions from major and minor glands is known as whole saliva and comprises 99% water. Other components include proteins, enzymes, electrolytes (Ca2+, Na+, K+, Cl-, HCO3, Mg2+), microorganisms, and exfoliated mucosal cells. Daily production is estimated to be between 0.5-1.5L. In terms of quality, saliva is generally described as serous, mucoid, or mucoserous with each type of secretion unique to respective major salivary glands.
Why is Saliva important?
As discussed, saliva is a versatile fluid with a heterogeneous composition, which enables it to perform critical functions necessary to maintain the health and integrity of oral soft and hard tissues. One of the simplest functions of saliva is lubrication, which facilitates speech, chewing, and swallowing. Furthermore, saliva enhances the sensation of taste, making meal times more enjoyable.
The process of food digestion also begins in the mouth through the actions of the salivary enzyme amylase on starch.
Harmful microbial activities are put in check by salivary antimicrobial components namely immunoglobulins, lysozymes, histatin, and lactoferrin. This is a vital role, considering the plethora of microbial commensals resident within the oral cavity.
Tooth remineralization is a necessary step for the prevention of dental caries. The presence of salivary ions such as Ca2+ and P ensures that enamel retains its integrity.
Due to its easy accessibility and non-invasive collection methods, saliva is increasingly gaining prominence as a valuable diagnostic tool for the detection of malignant neoplasms and infectious diseases, hormonal analysis, and forensic medicine.
References
5) Pedersen, A. M. L., Bardow, A., Jensen, S. B., & Nauntofte, B. (2002). Saliva and gastrointestinal functions of taste, mastication, swallowing and digestion. Oral Diseases, 8(3), 117-129. https://doi.org/10.1034/j.1601-0825.2002.02851.x
6) Greenberg MS, Glick M, Ship JA. Burket’s Oral Medicine, 11th Edition, Hamilton, DC Decker, 2008. Assessed and Endorsed by the MedReport Medical Review Board
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