Definição e significado de Saliva

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.^[1] 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.^[2] 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.^[3]

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.^[4] 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.

  Functions

  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.^[5] It also has a protective function, helping to prevent bacterial build-up on the teeth and washing away adhered food particles.

  Disinfectants

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.^[6] 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.^[7]

  Hormonal function

Saliva secretes hormone gustin, which is thought to play a role in the development of taste buds^{[citation needed]}. Saliva is not a harmful substance but a bacteria killer^{[citation needed]}. Saliva kills unwanted bacteria in the mouth, and throat^{[citation 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.^{[citation needed]}

  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.

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.^[3][9] 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.

  Contents

Produced in salivary glands, human saliva is 98% water, but it contains many important substances, including electrolytes, mucus, antibacterial compounds and various enzymes.^[1]

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
  • Iodine (mmol/L usually higher than plasma, but dependent variable according to dietary iodine intake)
• Mucus. Mucus in saliva mainly consists of mucopolysaccharides and glycoproteins;
• Antibacterial compounds (thiocyanate, hydrogen peroxide, and secretory immunoglobulin A)
• Epidermal growth factor or EGF
• 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.
    • Lysozyme
    • Salivary lactoperoxidase
    • Lactoferrin^[10]
    • Immunoglobulin A^[10]
  • 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.

  A building being renovated in the Carrollton section of New Orleans

  Spitting

Spitting or expectoration is the act of forcibly ejecting saliva or other substances from the mouth. It is often considered rude and a social taboo in many parts of the world, including Western^{[clarification needed]} countries – where it is frequently forbidden by local laws, because it was thought to facilitate the spread of disease; the laws are generally not strictly enforced. In some other parts of the world, expectoration is more socially acceptable (even if officially disapproved or illegal).

  References

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2011)

  Further reading

• Bahar, G; Feinmesser, R; Shpitzer, T; Popovtzer, A; Nagler, RM (2007). "Salivary analysis in oral cancer patients: DNA and protein oxidation, reactive nitrogen species, and antioxidant profile". Cancer 109 (1): 54–59. DOI:10.1002/cncr.22386. PMID 17099862. 
• Banerjee, RK; Bose, AK; Chakraborty, TK; De, SK; Datta, AG (1985). "Peroxidase-catalysed iodotyrosine formation in dispersed cells of mouse extrathyroidal tissues". J Endocrinol. 2: 159–165. PMID 2991413. 
• Banerjee, RK; Datta, AG (1986). "Salivary peroxidases". Mol Cell Biochem 70 (1): 21–29. PMID 3520291. 
• Bartelstone, HJ (1951). "Radioiodine penetration through intact enamel with uptake by bloodstream and thyroid gland". J Dent Res 5: 728–733. PMID 14888774. 
• Bartelstone, HJ; Mandel, ID; Oshry, E; Seildlin, SM (1947). "Use of radioactive iodine as a tracer in the Study of the Physiology of teeth". Science 106 (2745): 132. DOI:10.1126/science.106.2745.132-a. 
• Edgar, M; Dawes, C; O'Mullane, D (2004). Saliva and Oral Health: 3rd Edition. British Dental Association. ISBN 0-904588-87-4. 

  External links

Wikimedia Commons has media related to: Saliva

• The Wiktionary entry for saliva