Saliva 2007

[Autumn Pitz]

Theenzymes found in saliva are essential in beginning the process of digestion of dietary starches and fats. These enzymes also play a role in breaking down food particles entrapped within dental crevices, thus protecting teeth from bacterial decay.[2] Saliva also performs a lubricating function, wetting food and permitting the initiation of swallowing, and protecting the oral mucosa from drying out.[3]

The process of breaking down dietary carbohydrates and lipids starts with the enzymes present in saliva. In addition to keeping teeth free from bacterial decay, these enzymes aid in the breakdown of food particles stuck in dental fissures. In addition to lubricating food and enabling the start of swallowing, saliva also serves to prevent the mouth mucosa from drying up. Saliva has specialized purposes for a variety of animal species beyond predigestion. Certain swifts construct nests with their sticky saliva. The foundation of bird's nest soup is an aerodramus nest. Venomous saliva injected by fangs is used by cobras, vipers, and certain other members of the venom clade to hunt. Some caterpillars use modified salivary glands to store silk proteins, which they then use to make silk fiber.[4]

Produced in salivary glands, human saliva comprises 99.5% water, but also contains many important substances, including electrolytes, mucus, antibacterial compounds and various enzymes.[1] Medically, constituents of saliva can noninvasively provide important diagnostic information related to oral and systemic diseases.[5]

Experts debate the amount of saliva that a healthy person produces. Production is estimated at 1500ml per day and researchers generally accept that during sleep the amount drops significantly.[3][9]In humans, the submandibular gland contributes around 70 to 75% of secretions, while the parotid gland secretes about 20 to 25%; small amounts are secreted from the other salivary glands.[10]

Saliva contributes to the digestion of food and to the maintenance of oral hygiene. Without normal salivary function the frequency of dental caries, gum disease (gingivitis and periodontitis), and other oral problems increases significantly.[citation needed] Saliva limits the growth of bacterial pathogens and is a major factor in sustaining systemic and oral health through the prevention of tooth decay and the removal of sugars and other food sources for microbes.[11]

Saliva coats the oral mucosa mechanically protecting it from trauma during eating, swallowing, and speaking. Mouth soreness is very common in people with reduced saliva (xerostomia) and food (especially dry food) sticks to the inside of the mouth.

The digestive functions of saliva include moistening food and helping to create a food bolus. The lubricative function of saliva allows the food bolus to be passed easily from the mouth into the esophagus. Saliva contains the enzyme amylase, also called ptyalin, which is capable of breaking down starch into simpler sugars such as maltose and dextrin that can be further broken down in the small intestine. About 30% of starch digestion takes place in the mouth cavity. Salivary glands also secrete salivary lipase (a more potent form of lipase) to begin fat digestion. Salivary lipase plays a large role in fat digestion in newborn infants as their pancreatic lipase still needs some time to develop.[12]

Saliva is very important in the sense of taste. It is the liquid medium in which chemicals are carried to taste receptor cells (mostly associated with lingual papillae). People with little saliva often complain of dysgeusia (i.e. disordered taste, e.g. reduced ability to taste, or having a bad, metallic taste at all times). A rare condition identified to affect taste is that of 'Saliva Hypernatrium', or excessive amounts of sodium in saliva that is not caused by any other condition (e.g., Sjgren syndrome), causing everything to taste 'salty'.

Parasympathetic stimulation leads to acetylcholine (ACh) release onto the salivary acinar cells. ACh binds to muscarinic receptors, specifically M3, 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. ACh also causes the salivary gland to release kallikrein, an enzyme that converts kininogen to lysyl-bradykinin. Lysyl-bradykinin acts upon blood vessels and capillaries of the salivary gland to generate vasodilation and increased capillary permeability, respectively. The resulting increased blood flow to the acini allows the production of more saliva. In addition, Substance P can bind to Tachykinin NK-1 receptors leading to increased intracellular calcium concentrations and subsequently increased saliva secretion. Lastly, both parasympathetic and sympathetic nervous stimulation can lead to myoepithelium contraction which causes the expulsion of secretions from the secretory acinus into the ducts and eventually to the oral cavity.

Sympathetic stimulation results in the release of norepinephrine. Norepinephrine binding to α-adrenergic receptors will cause an increase in intracellular calcium levels leading to more fluid vs. protein secretion. If norepinephrine binds β-adrenergic receptors, it will result in more protein or enzyme secretion vs. fluid secretion. Stimulation by norepinephrine initially decreases blood flow to the salivary glands due to constriction of blood vessels but this effect is overtaken by vasodilation caused by various local vasodilators.

Spitting is the act of forcibly ejecting saliva or other substances from the mouth. In many parts of the world, it is considered rude and a social taboo, and has sometimes been outlawed. In some countries, for example, it has been outlawed for reasons of public decency and attempting to reduce the spread of disease. These laws may not strictly enforced, but in Singapore, the fine for spitting may be as high as SGD$2,000 for multiple offenses, and one can even be arrested.[citation needed] In China, expectoration is more socially acceptable (even if officially disapproved of or illegal), and spittoons are still a common appearance in some cultures. Some animals, even humans in some cases, use spitting as an automatic defensive maneuver. Camels are well known for doing this, though most domestic camels are trained not to.

Many birds in the swift family, Apodidae, produce a viscous saliva during nesting season to glue together materials to construct a nest.[18] Two species of swifts in the genus Aerodramus build their nests using only their saliva, the base for bird's nest soup.[19]

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 mucin, IgA, lactoferrin, lysozyme and peroxidase.[20][21] 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.

In Pavlov's experiment, dogs were conditioned to salivate in response to a ringing bell; this stimulus is associated with a meal or hunger. Salivary secretion is also associated with nausea. Saliva is usually formed in the mouth through an act called gleeking, which can be voluntary or involuntary.

Dry mouth also makes you more likely to develop rapid tooth decay and gum (periodontal) disease. That's because saliva helps clear food particles from your teeth. This helps reduce your risk for cavities.

Dry mouth is common in older adults, although the reasons are unclear. Diseases that affect the whole body (systemic disorders), poor nutrition, and the use of certain drugs are thought to play a key role.

If dry mouth persists, your doctor or dentist may recommend rinsing your mouth with artificial saliva. Artificial saliva is a liquid or spray sold without a prescription. It can be used as often as needed.

Too much saliva is usually not something to worry about unless it persists. It's normal to make more or less saliva depending on what you eat or drink. Your body usually takes care of excess saliva by swallowing more.

It is normal for your salivary glands to go into overdrive when you eat very spicy foods. Taste buds on your tongue play a big role in how much saliva you make. Pop something spicy or very sour in your mouth and your taste buds react by telling your body to make more saliva. Acidic foods tend to trigger a lot more saliva than sweet foods. If excess saliva bothers you, try changing your diet.

If you have problems swallowing, you may feel like you have a lot of saliva in your mouth and may drool. Chronic drooling is most often seen in people who have poor muscle control in the face and mouth.

Your doctor will probably first recommend a prescription medicine to help reduce the amount of saliva you make. Such medicines include glycopyrrolate and scopolamine. Common side effects include problems urinating, a fast heartbeat, dizziness, blurred vision, and sleepiness.

If you have severe drooling, your doctor may suggest Botox injections into one or more salivary glands. This treatment is considered safe, but results only last a few months. You will need to have more Botox shots in the future.

Saliva collection devices and reagent for the collection, transport, and storage of saliva samples. Included reagent DNA/RNA Shield inactivates infectious agents within saliva and stabilizes nucleic acid at the point of saliva collection.

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