Saliva

Saliva (commonly referred to as spit, drool or slobber) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be extracted), enzymes (such as lingual lipase and amylase), and antimicrobial agents (such as secretory IgA, and lysozymes).^[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 trapped 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]

Saliva has specialized purposes for a variety of animal species beyond predigestion. Certain swifts construct nests with their sticky saliva, such as Aerodramus, whose nest is consumed by humans as bird's nest soup. 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]

• Water: 99.5%
• Electrolytes:
  • 2–21 mmol/L sodium (lower than blood plasma)
  • Potasio de 10 a 36  mmol/L (superior al del plasma)
  • 1,2–2,8  mmol/L de calcio (similar al del plasma)
  • 0,08–0,5  mmol/L de magnesio
  • Cloruro de 5 a 40  mmol/L (inferior al del plasma)
  • 25  mmol/L de bicarbonato (superior al del plasma)
  • 1,4–39  mmol/L de fosfato
  • Yodo (la concentración en mmol/L suele ser mayor que en el plasma, pero es una variable dependiente según la ingesta de yodo en la dieta).
• Moco (el moco en la saliva se compone principalmente de mucopolisacáridos y glicoproteínas )
• Compuestos antibacterianos ( tiocianato , peróxido de hidrógeno e inmunoglobulina A secretora )
• Factor de crecimiento epidérmico (EGF)
• La saliva elimina el cesio , que puede sustituir al potasio en las células. ^{[ 6 ] [ 7 ]}
• Diversas enzimas ; en particular:
  • La α-amilasa (EC3.2.1.1), o ptialina, secretada por las células acinares de las glándulas parótida y submandibular, inicia la digestión del almidón antes de que se degluta el alimento; tiene un pH óptimo de 7,4.
  • La lipasa lingual, secretada por las células acinares de la glándula sublingual, tiene un pH óptimo de alrededor de 4,0, por lo que no se activa hasta que entra en el ambiente ácido del estómago.
  • La calicreína es una enzima que escinde proteolíticamente el quininógeno de alto peso molecular para producir bradicinina ; es secretada por las células acinares de las tres glándulas salivales principales.
  • Enzimas antimicrobianas que matan las bacterias:
    • Lisozima
    • lactoperoxidasa salival
    • Lactoferrina ^{[ 8 ]}
    • Inmunoglobulina A ^{[ 8 ]}
    • Beta defensina
  • Proteínas ricas en prolina (función en la formación del esmalte , unión de Ca ²⁺ , eliminación de microbios y lubricación) ^{[ 8 ]}
  • Enzimas menores que incluyen: fosfatasas ácidas salivales A y B, N-acetilmuramoil-L-alanina amidasa , NAD(P)H deshidrogenasa (quinona) , superóxido dismutasa , glutatión transferasa , aldehído deshidrogenasa de clase 3 , glucosa-6-fosfato isomerasa y calicreína tisular (función desconocida) ^{[ 8 ].}
• Cells: possibly as many 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 a foul odor.
• Opiorphin, a pain-killing substance found in human saliva
• Haptocorrin, a protein which binds to vitamin B₁₂ to protect it against degradation in the stomach, before it binds to intrinsic factor.

Experts debate the amount of saliva that a healthy person produces. Production is estimated at 1,500 mL 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]

Via the action of amylase and other enzymes, saliva contributes to the digestion of food and to the maintenance of oral hygiene.^[11] Saliva limits the growth of bacterial pathogens and is a major factor in sustaining systemic and oral health through the prevention of tooth decay.^[11] Saliva also acts as a buffer, reducing acidity of food components by its bicarbonate and phosphate content.^[11]

La producción de saliva es estimulada tanto por el sistema nervioso simpático como por el parasimpático . ^{[ 19 ]}

La estimulación simpática de la saliva facilita la respiración , mientras que la estimulación parasimpática facilita la digestión.

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 TachykininNK-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.

Saliva production may also be pharmacologically stimulated by the so-called sialagogues. It can also be suppressed by the so-called antisialagogues.

Existen sustitutos de la saliva disponibles comercialmente . ^{[ 24 ]}

• Número de reproducción básico
• saliva en ayunas

• The dictionary definition of saliva at Wiktionary