Saliva

Saliva is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is 99.5⁠% water plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be extracted), enzymes (such as amylase and lipase), antimicrobial agents such as secretory IgA, and lysozymes. Saliva is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is 99.5⁠% water plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be extracted), enzymes (such as amylase and lipase), antimicrobial agents such as secretory IgA, and lysozymes. 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, thus protecting teeth from bacterial decay. Saliva also performs a lubricating function, wetting food and permitting the initiation of swallowing, and protecting the oral mucosa from drying out. Various animal species have special uses for saliva that go beyond predigestion. Some swifts use their gummy saliva to build nests. Aerodramus nests form the basis of bird's nest soup.Cobras, vipers, and certain other members of the venom clade hunt with venomous saliva injected by fangs. Some caterpillars produce silk fiber from silk proteins stored in modified salivary glands. Produced in salivary glands, human saliva is 99.5% water, but also contains many important substances, including electrolytes, mucus, antibacterial compounds and various enzymes. There is much debate about the amount of saliva that is produced in a healthy person per day; estimates range from 6 to 15 litres per day while it is generally accepted that during sleep the amount nearly triples.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. 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. 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 oesophagus. 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% 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. 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). Persons 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).