Saliva
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- For the band, see Saliva (band).
Saliva, often informally known as spit, is the moist, clear, and usually somewhat frothy substance produced in the mouths of some animals, including humans. To spit or the action of spitting is to expel saliva or other substances from the mouth. A verb for this action is expectoration.
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Contents of Saliva
In animals, saliva is produced in and secreted from the salivary glands. It is a fluid containing:
- Electrolytes: (2-21 mmol/L sodium, 10-36 mmol/L potassium, 1.2-2.8 mmol/L calcium, 0.08-0.5 mmol/L magnesium, 5-40 mmol/L chloride, 2-13 mmol/L bicarbonate, 1.4-39 mmol/L phosphate)
- Mucus. Mucus in saliva mainly consists of mucopolysaccharides and glycoproteins;
- Antibacterial compounds (thiocyanate, hydrogen peroxide, and secretory immunoglobulin A)
- Various enzymes. The major enzymes found in human saliva are alpha-amylase (EC3.2.1.1), lysozyme (EC3.2.1.17), and lingual lipase (EC3.1.1.3). 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 has a pH optimum ~4.0 so it is not activated till entering an acidic environment. Lysozyme acts to lyse bacteria. Human saliva contains also salivary acid phosphatases A+B (EC3.1.3.2), N-acetylmuramyl-L-alanine amidase (EC3.5.1.28), NAD(P)H dehydrogenase-quinone (EC1.6.99.2), salivary lactoperoxidase (EC1.11.1.7), superoxide dismutase(EC1.15.1.1), glutathione transferase (EC2.5.1.18), class 3 aldehyde dehydrogenase (EC1.2.1.3), glucose-6-phosphate isomerase (EC5.3.1.9), and tissue kallikrein (EC3.4.21.35). The presence of these things causes saliva to sometimes have a foul odor.
Healthy people produce about 1.5 L of saliva per day.
Functions
The functions of saliva include moistening food so it can be swallowed easily. Also, saliva contains the enzyme amylase, also called ptyalin, that breaks some starches down into maltose and dextrin.
(From Encyclopædia Britannica School Edition)
Saliva also protects teeth from decay by plaque. After eating food or drinking, plaque bacteria ferment with the sugars and starches that were in previously eaten foods to produce acid. After 5 to 10 minutes of creating the acid, the teeth environment can reach a point called demineralization, which is when the pH level is low enough to start decaying teeth. Saliva is used to neutralize these acids therefore helping to prevent demineralization. Remineralization is when saliva helps repair the damaged crystals of the tooth enamel.
Beliefs
A common belief is that saliva contained in the mouth has natural disinfectants, which leads people to believe it is beneficial to "lick their wounds". Researchers at the University of Florida at Gainesville have discovered a protein called nerve growth factor (NGF) in the saliva of mice. Wounds doused with NGF healed twice as fast as untreated and unlicked wounds; therefore, saliva does have some curative powers in some species. NGF has not been found in human saliva; however, researchers find human saliva contains such antibacterial agents as secretory IgA, lactoferrin, and lactoperoxidase. It has not been shown that licking your wounds actually disinfects them.
See also
de:Speichel es:Saliva fr:Salive io:Salivo it:Saliva he:רוק (ביולוגיה) lt:Seilės nl:Speeksel ja:唾液 pl:Ślina pt:Saliva ru:Слюна fi:Sylki sv:Saliv zh:唾液