Saliva Production

This article is about the substance produced in the mouths of humans. For genus of a plant Salvia, see Salvia. For other uses, see Saliva (disambiguation). Saliva is the watery substance produced in the mouths of humans and most animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands: the parotid, sublingual, and submandibular glands. Hundreds of other minor salivary glands also contribute to the production of saliva. Human saliva is composed of 98% water, while the other 2% consists of electrolytes, mucus, glycoproteins, enzymes, and antibacterial compounds such as secretory IgA and lysozyme. The enzymes 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, protecting teeth from bacterial decay. Furthermore, saliva serves a lubricative function, wetting food and permitting the initiation of swallowing, and protecting the mucosal surfaces of the oral cavity from desiccation. Various species have special uses for saliva that go beyond predigestion. Some swifts use their gummy saliva to build nests. Aerodramus nests are prized for use in bird's nest soup. 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.''



Digestion

The digestive functions of saliva include moistening food and helping to create a food bolus. This 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), and is thus capable of breaking down starch into simpler sugars that can be later absorbed or further broken down in the small intestine. 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. It also has a protective function, helping to prevent bacterial build-up on the teeth and washing away adhered food particles.''

Disinfectants

See also: 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, lysozyme and peroxidase. 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 and 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.''

Hormonal function

Saliva secretes hormone gustin, which is thought to play a role in the development of taste budscitation needed. Saliva is not a harmful substance but a bacteria killercitation needed. Saliva kills unwanted bacteria in the mouth, and throatcitation needed.''

Iodine in salivary glands and oral health

The trophic, antioxidant and apoptosis-inductor actions and the presumed anti-tumour activity of iodide might also be important for prevention of oral and salivary glands diseases.''

Stimulation

The production of saliva is stimulated both by the sympathetic nervous system and the parasympathetic. The saliva stimulated by sympathetic innervation is thicker, and saliva stimulated parasympathetically is more watery.''

Sympathetic stimulation of saliva is to facilitate respiration, whereas parasympathetic stimulation is to facilitate digestion. 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. Saliva production may also be pharmacologically stimulated by so called sialagogues. It can also be suppressed by so called antisialagogues.''

Daily salivary output

There is much debate about the amount of saliva that is produced in a healthy person per day; estimates range from 0.75 to 1.5 liters per day while it is generally accepted that during sleep the amount drops to almost zero. In humans, the submandibular gland contributes around 70–75% of secretion, while the parotid gland secretes about 20–25 % and small amounts are secreted from the other salivary glands.''
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