The watery mixture of secretions from the salivary and oral mucous glands that lubricates chewed food, moistens the oral walls, and contains ptyalin.
[Latin salīva.]
saliva
Dictionary:
sa·li·va (sə-lī'və)  |
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| World of the Body: saliva |
Saliva is a complex fluid secreted into the mouth by the various salivary glands. There are three pairs of major salivary glands: the parotid glands, situated behind the jaw in front of the ear, and the submandibular and sublingual glands that lie under the jaw and tongue. Also, there are many minor salivary glands, present throughout the mouth within the lips, cheeks, tongue, and palate. The parotid glands produce saliva with a watery (serous) consistency, whilst the sublingual and the minor salivary glands produce a more viscous (mucous) fluid. The submandibular glands produce a mixture of serous and mucous saliva.
Saliva contains 99% water, plus dissolved inorganic ions and numerous organic substances. Most of the organic material in saliva is protein, some of which is glycoprotein or mucin, which contains both carbohydrate and protein components. The total daily flow of saliva from all the salivary glands is around 600 ml. Salivary flow rates are lowest during sleep and highest whilst eating, when flow rates may reach 5 ml/min. Resting salivary flow averages around 0.3 ml/min. Salivary flow rates are reduced in dehydration and after significant blood loss. The resulting dry mouth is responsible for the accompanying sensation of thirst.
Although saliva is very useful for moistening postage stamps and cotton thread, its main roles are in feeding, and in protecting the oral tissues. When salivary flow is too low, dry mouth (xerostomia) may result. Here, normal oral functions such as chewing, swallowing, and speaking can be uncomfortable and difficult to perform. Greatly reduced salivary flow may also result in increased incidence of dental disease (dental caries and periodontal disease), or disease of the oral mucosa — the lining of the mouth (stomatitis). Dry mouth may be due to salivary gland disorders, but it is also a prominent and undesirable side-effect of many commonly-used drugs.
Saliva coats the surfaces of the teeth and oral mucosa with a thin film of mucins. This slippery film lubricates the oral tissues, making it easier to chew, swallow, and speak. Saliva assists feeding by moistening the ingested food morsels and helps to bind the chewed food particles into a compact mass (a bolus) suitable for swallowing.
enzymes in saliva begin the digestive process: an a-amylase breaks down starch molecules and a lipase digests fat. Saliva also contributes to taste by dissolving sapid substances in food and so making them accessible to the taste buds; a zinc-binding protein, gustin, is thought to contribute to the taste process.
The saliva also has defensive functions. ‘Proline-rich proteins’ coat the teeth with a thin layer — pellicle — that serves as a protective diffusion barrier on the tooth surface. Saliva is supersaturated with calcium and phosphate ions, which are effectively in balance with the minerals in the teeth. To a limited extent, calcium and phosphate ions in saliva can diffuse through the pellicle into the tooth and can reverse the very early stages of tooth decay, where acids have caused slight demineralization of the tooth surface, but before actual cavity formation occurs. This remineralization process is enhanced by fluoride ions, which may be present in toothpastes or other oral health products. While the high levels of calcium and phosphate in saliva may help remineralization of early carious lesions, they also increase the likelihood of spontaneous precipitation of calcium phosphates on the teeth as calculus (tartar). However, saliva also contains statherins and proline-rich proteins, which inhibit mineralization and so help to prevent precipitation of calcium and phosphate on intact tooth surfaces. Saliva contains all the ions usually present in body fluids, and of these, bicarbonate (hydrogen carbonate) ions play a major role in determining the pH and buffering capacity of saliva. Salivary bicarbonate can help protect teeth against attack from acids produced by bacteria in dental plaque. The bicarbonate concentration of saliva increases with flow rate, so buffering is improved during eating.
Salivary proteins prevent the oral mucosa from drying and provide a defensive barrier against bacteria, fungi, and viruses. Saliva contains growth factors which promote healing of the oral mucosa. Saliva contains various antimicrobial substances, including lysozyme, lactoferrin, sialoperoxidase, and histatins as well as more specific antibodies or immunoglobins. The main antibody in saliva is secretory immunoglobin A (sIgA), which binds to bacterial antigens and is of interest in view of its possible role in immunity to dental caries.
Salivary flow increases during eating. The physical action of chewing stimulates nerve endings in the periodontal tissues around the teeth. Sapid substances stimulate taste buds. Both of these stimuli are potent initiators of salivary flow. Olfactory (smell) stimuli have little effect in provoking salivary flow in humans, although irritants (such as spices) can increase salivary flow. Signals from nerve endings in the mouth evoke salivation by exciting the salivatory centres in the brainstem. Salivary secretion is controlled by the autonomic nervous system. The sympathetic and parasympathetic divisions of the autonomic nervous system often have antagonistic actions, but in the control of salivation they act in a complementary manner. Activation of the parasympathetic nerves elicits large volumes of a watery salivary secretion containing ions and enzymes; stimulation of the sympathetic nerves produces small amounts of saliva that is rich in proteins. The composition of saliva thus varies with the balance of activity in the autonomic nerves controlling salivary secretion.
Salivary responses to chewing and taste stimuli are innate. However, salivary flow may be elicited by events not necessarily associated with feeding. These are termed conditioned reflexes and are learned after a period of training or conditioning during which a ‘natural’ stimulus (e.g. food) is presented at the same time as the ‘artificial’ or conditioning stimulus (e.g. light or sound). Eventually, the ‘artificial’ stimulus on its own will elicit salivary flow. The classical example of conditioned salivary secretion was originally observed in dogs by the Russian physiologist, Ivan Pavlov, who was awarded a Nobel Prize in 1904 for his work on digestive secretions. Conditioned salivary secretion is also present in humans.
— Robin Orchardson
Bibliography
- Edgar, W. M. and O'Mullane, D. M. (ed.) (1996). Saliva and oral health, (
2nd edn ). British Dental Association, London
See also alimentary system; eating; mouth.
| Food and Nutrition: saliva |
Secretion of the salivary glands in the mouth: 1-1.5 L secreted daily. A dilute solution of the protein mucin (which lubricates food) and the enzyme amylase (which hydrolyses starch), with small quantities of urea, potassium thiocyanate, sodium chloride, and bicarbonate.
| Dental Dictionary: saliva |
(səlī′və)
n
n
The clear muco-serous secretion formed mainly in the major glands of the parotid, submandibular, and sublingual, as well as minor glands. It has lubricative, cleansing, microbial, excretory, and digestive functions and also is an aid to deglutition. While its pH level is slightly more acidic than blood—6.3 to 6.9—it is more basic than dental plaque and acts as a buffering agent within the oral cavity. Emotional disturbances affect the rate of salivary secretion either by stimulation of secretion or inhibition of activity, leading to xerostomia. A lowered rate of flow has been noted in patients suffering from depression, whereas a higher degree of salivary activity has been observed in patients with mania. However, most xerostomia is due to S medications and is related to an increased caries risk.
| Britannica Concise Encyclopedia: saliva |
For more information on saliva, visit Britannica.com.
| Sports Science and Medicine: saliva |
A viscous, transparent, alkaline liquid containing water, salts, mucin (a glycoprotein), immunoglobulins (see salivary immunoglobulin A), and enzymes (e.g. salivary amylase). Saliva prevents the buccal cavity from drying out, acts as a lubricant for the passage of food into the oesophagus, and starts the digestion of starch.
| Health Dictionary: saliva |
(suh-leye-vuh)
The fluid produced by the secretions of the salivary glands. Saliva contains enzymes that begin the digestion of starches. It also moistens the mouth tissues and makes food easier to chew and swallow.
| Veterinary Dictionary: saliva |
The enzyme-containing secretion of the salivary glands.
- s. tests — tests conducted on the saliva of horses competing in races or show events to detect the presence of drugs used to affect the horse's performance.
| Word Tutor: saliva |
IN BRIEF: The liquid released by glands that keeps the mouth moist; drool.
Death is caused by swallowing small amounts of saliva over a long period of time.
— George Carlin, American stand-up comedian.
| Wikipedia: Saliva |
For other uses, see Saliva (disambiguation).
Not to be confused with Salvia.
Not to be confused with Saliva (band).
 |
Look up saliva in Wiktionary, the free dictionary. |
Saliva (also referred to as spit or spittle) is the watery and usually frothy substance produced in the mouths of humans and most other animals. Saliva is produced in and secreted from the salivary glands. Human saliva is composed mostly of water, but also includes electrolytes, mucus, antibacterial compounds, and various enzymes. [1] 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. [2]
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.[3] 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 |
Functions
Digestion
The digestive functions of saliva include moistening food, and helping to create a food bolus, so it can be swallowed easily. Saliva contains the enzyme amylase that breaks some starches down into maltose and dextrin. Thus, digestion of food begins in the mouth. Salivary glands also secrete enzymes (salivary lipase) to start fat digestion.[4]
Disinfectants
Further information: Wound licking
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 can help to heal wounds 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 peroxidase.[5] It has not been shown that human licking of wounds disinfects them, but licking is likely to help clean the wound by removing larger contaminants such as dirt and may help to directly remove infective bodies by brushing them away. Therefore, licking would be a way of wiping off pathogens, useful if clean water is not available to the animal or person.
The mouth of animals is the habitat of many bacteria, some pathogenic. Some diseases, such as herpes, can be transmitted through the mouth. Animal (including human) bites are routinely treated with systemic antibiotics because of the risk of septicemia.
Recent research suggests that the saliva of birds is a better indicator of avian influenza than are faecal samples. [6]
Non-physiological use
Saliva has anti-fog functions. Scuba divers commonly smear a thin layer of saliva on the inside surface of their goggles to prevent fogging.
Saliva is an effective cleaning agent used in art conservation. Cotton swabs coated with saliva are rolled across a painting's surface to delicately remove thin layers of dirt that may accumulate.[7]
Stimulation
The production of saliva is stimulated both by the sympathetic nervous system and the parasympathetic.[8]
The saliva stimulated by sympathetic innervation is thicker, and saliva stimulated parasympathetically is more watery.
Parasympathetic stimulation leads to acetylcholine (ACh) release onto the salivary acinar cells. ACh binds to muscarinic receptors and causes an increased intracellular calcium ion concentration (through the IP3/DAG second messenger system). Increased calcium causes vesicles within the cells to fuse with the apical cell membrane leading to secretion formation. ACh also causes the salivary gland to release kallikrein, an enzyme that converts kininogen to lysyl-bradykinin. Lysyl-bradykinin acts upons blood vessels and capillaries of the salivary gland to generate vasodilation and increased capillary permeability respectively. The resulting increased blood flow to the acinar allows production of more saliva. Lastly, both parasympathetic and sympathetic nervous stimulation can lead to myoepitheilium contraction which causes the expulsion of secretions from the secretory acinus into the ducts and eventually to the oral cavity.
Daily salivary output
There is much debate about the amount of saliva that is produced in a healthy person per day. The estimates range from 0.75 liters per day to 1.5 liters per day. This suggests that the amount produced varies from person to person. However, it is generally accepted that while sleeping the amount usually drops to almost zero.
Contents
Produced in salivary glands, human saliva is 98% water, but it contains many important substances, including electrolytes, mucus, antibacterial compounds and various enzymes. [9]
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
- Mucus. Mucus in saliva mainly consists of mucopolysaccharides and glycoproteins;
- Antibacterial compounds (thiocyanate, hydrogen peroxide, and secretory immunoglobulin A)
- 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.
- Proline-rich proteins (function in enamel formation, Ca2+-binding, microbe killing and lubrication)[10]
- 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)[10].
- 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
- ^ Physiology at MCG 6/6ch4/s6ch4_6
- ^ Christian Starkenmann, Benedicte Le Calvé, Yvan Niclass, Isabelle Cayeux, Sabine Beccucci, and Myriam Troccaz. Olfactory Perception of Cysteine−S-Conjugates from Fruits and Vegetables. J. Agric. Food Chem., 2008; 56 (20): 9575-9580 DOI: 10.1021/jf801873h
- ^ Marcone, M. F. (2005). "Characterization of the edible bird's nest the Caviar of the East." Food Research International 38:1125–1134. doi:10.1016/j.foodres.2005.02.008 Abstract retrieved 12 Nov 2007
- ^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1.
- ^ Jorma Tenovuo: Antimicrobial Agents in Saliva—Protection for the Whole Body. Journal of Dental Research 2002, 81(12):807-809
- ^ "Saliva swabs for bird flu virus more effective than faecal samples" German Press Agency December 11, 2006 Retrieved 13 November 2007
- ^ "Techniques for Cleaning Acrylic". Golden Artist Colors. http://www.goldenpaints.com/justpaint/jp5article2.php. Retrieved on 2008-09-12.
- ^ Physiology at MCG 6/6ch4/s6ch4_7
- ^ Physiology at MCG 6/6ch4/s6ch4_6
- ^ a b c d Page 928 in: Walter F., PhD. Boron (2003). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. pp. 1300. ISBN 1-4160-2328-3.
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| Translations: Saliva |
Deutsch (German)
n. - Speichel
Ελληνική (Greek)
n. - (φυσιολ.) σίελος, σάλιο
Português (Portuguese)
n. - saliva (f)
Svenska (Swedish)
n. - saliv, spott
中文（简体）(Chinese (Simplified))
口水, 唾液
中文（繁體）(Chinese (Traditional))
n. - 口水, 唾液
العربيه (Arabic)
(الاسم) لعاب
עברית (Hebrew)
n. - רוק, ריר
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| World of the Body. The Oxford Companion to the Body. Copyright © 2001, 2003 by Oxford University Press. All rights reserved. Read more |
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| Food and Nutrition. A Dictionary of Food and Nutrition. Copyright © 1995, 2003, 2005 by A. E. Bender and D. A. Bender. All rights reserved. Read more |
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