Saliva is a clear and viscous liquid found in the mouth of humans and other animals. It provides lubrication, and also helps in the initial steps of digestion of foods. Saliva is produced by either major salivary glands, each present in pairs: parotid, submandibular, and sublingual. Saliva is also produced by minor salivary glands that are present all over the mouth and the surrounding areas. Minor salivary glands are very small and their number is between 800 to 1000.
The saliva produced by those glands is either mucous (thick and slippery fluid), serous (watery fluid), or seromucous (a mix of both). Mucous saliva provides lubrication of the mouth because of the protein called mucin. Serous saliva breaks down carbohydrates to smaller chunks of food with the help of the secreted protein called alpha-amylase.
Humans produce between 0.5 and 1.5 litre of saliva every day. All that saliva is essential in the initial steps of digestion, because saliva moistens and breaks down ingested foods, and keeps the mouth humid and healthy.
Composition of saliva
Saliva is made out of 99.5% of water. The remaining constituents are very important in its function, and they include electrolytes, mucus, proteins and enzymes, and also antibacterial agents. It’s important to note that, even if these components have different functions, saliva acts as a whole biologic fluid. Proteins in saliva have more than one function, which can be amphifunctional (acting both for and against the person with functions that are not comparable), or redundant (two or more different proteins that perform similar functions but to different extents).
Electrolytes (bicarbonates, phosphates, sodium, potassium, calcium, magnesium, chloride and iodine) act to control pH (acidity) of saliva. The pH of normal saliva ranges from 5.3 to 7.8, with an average of 6 to 7, which means that it’s slightly acidic.
Proteins such as mucins, act to cleanse, and attach micro-organisms to dental plaque that contribute in its metabolism.
Other proteins, as well as electrolytes like phosphates and calcium, work together to modulate demineralization and remineralization of teeth.
Proteins such as immunoglobulins (antibodies) and other enzymes provide antibacterial action that protects teeth and gums.
Functions of saliva
The components found in saliva work together in multifunction roles, which can together be beneficial and detrimental for the person’s oral health. Saliva is essential for the digestion of food and the maintenance of oral hygiene. Without a normal amount of saliva in the mouth, there would be an increase in the frequency of dental caries, gum disease, and other oral problems.
Digestion. Saliva has an early, initiative role in total digestion by moistening food, and breaking down of starch into maltose and dextrin with the help of the enzyme called amylase (sometimes called ptyalin). Food is then transformed into a bolus, which is lubricated by saliva, and is then allowed to pass easily from the mouth into the oesophagus. About 30% of starch digestion takes place in the mouth. Lipase is another enzyme present in saliva, which begins fat digestion.
Taste. Saliva is very important in enhancing taste. Some zinc-binding proteins available in saliva are carried to taste buds of the tongue, which enhances tasting capability. People with little saliva often complain of a reduced ability of taste (dysgeusia). Some people have a rare condition called hypernatrium, which is an abnormally high amount of sodium in saliva.
Lubrication and protection. Saliva provides a sero-mucous coating on oral tissues, acting as a barrier against irritants. This protects mechanically from mini-trauma during eating, swallowing, and speaking. The best lubricating elements from saliva are called mucins, which are produced by minor salivary glands. Mucins are polypeptides (long and linear proteins) that are viscous, elastic, have a strong adhesive property, and do not dissolve easily in liquids. Therefore mucins offer protection to gums, cheeks, and other tissues in the mouth, from contacts with teeth, foods, and also dentures. Soreness of the mouth may occur in people with reduced saliva (xerostomia) when food (especially dry food) sticks to oral tissues.
Antibacterial activity. Salivary glands secrete different agents to protect teeth and tissues. Immunologic agents include antibodies of the IgA, IgG and IgM classes, where the IgA antibodies are the most common: they neutralize viruses, and prevent some bacteria from attaching to teeth and gums. Non-immunologic protection is provided by other proteins, mucins and enzymes. These work to prevent bacteria from assembling, also reducing their ability to stick to teeth and other tissues of the mouth.
Buffering action and clearance. Saliva has a buffering (moderating) capacity which neutralizes acids in the mouth. This function is allowed by some salivary components such as bicarbonate, phosphate, urea, and various proteins (enzymes). The buffering action works better when saliva is highly stimulated in the mouth, producing high flow rates, like when healthy people eat something. The neutralization of acids in dental plaque provides a natural protection against dental caries.
Maintenance of tooth integrity. This dental upkeep is based on the demineralization and remineralization processes. Demineralization is the process of removing minerals from enamel and dentin, caused by acidic foods and drinks, or by acids produced by bacteria that digest foods. Remineralization is when lost amounts of the enamel are replaced with minerals from the saliva. For this manner to occur, minerals in the saliva have to be supersaturated, which means that they have to be available in quantities higher than the soluble amount of the minerals in saliva. These minerals are calcium and phosphate, and they are helped by salivary proteins for the maturation and remineralization of enamel. Because saliva flow is important in this process, patients that may have systemic disease, or taking multiple drugs, may have a decreased amount of saliva in the mouth (xerostomia). For those patients, fluoride supplements can promote remineralization of teeth.
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- Wikipedia, (Saliva).
The information above should be used as a reference only. Any medical decision should not be taken before consulting a health care professional.