Saliva is a fluid produced in the mouths of most animals. In humans it is produced by three pairs of salivary glands, the parotids in each cheek over the jaw and in front of the ears, the submandibular glands at the back of the mouth on both sides of the jaw, and the sublingual glands, which are under the floor of the mouth. They drain into various parts of the mouth, and there are another 600-1000 tiny glands called minor salivary glands in the lips, inner cheek, and the lining of the mouth and throat. Altogether they produce one to three pints of fluid a day.
Obviously a lot of this is used keeping the mouth moist. Anyone who’s given a long speech, told a long story, or had a cold that made them breathe through their mouth knows the drying effect of air on the mouth lining. But saliva has many other functions.
The mouth is home to a host of microbes, molds, and yeasts. It’s one of the easiest routes for these things to get in the body, but a careful balance of of electrolytes like sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphate, and iodine maintains an environment that’s not too hospitable to any of them, but neutral enough to keep them balanced. In a normal saliva environment neither yeast nor bacteria nor mold can gain an upper hand, thwarting infection.
On top of this electrolyte balancing act, antibacterial components like thiocyanate and hydrogen peroxide in saliva combine in the mouth to form a potent antibacterial agent when certain enzymes are secreted. The enzyme lysozyme in saliva is on its own an antibacterial, and saliva carries other antibacterial, antiviral, and anti-parasitic components.
But above all else, saliva aids digestion. It’s obvious role is to moisten food and make it easier to swallow. Without saliva, food would sop up the moisture from the mucous membranes that line your mouth and leave you with a dry paste to swallow. Saliva allows your mouth to form moist lumps that slide down your throat easily.
Your saliva also contains mucous,the primary lubricant and protectant produced by the tissues that line your throat, nose, stomach, and even intestines. Different mixes of water and mucous come from your salivary glands depending on the food you eat. Mucous from the parotids (in the cheeks) tends to be watery and flows more freely when you’re eating drier or more fibrous foods, while the sublingual glands under the toungue produce saliva with more mucous and become more active when eating fatty foods. The submandibular glands at the back of the mouth provide a more balanced mix.
Saliva also contains the enzyme amylase that breaks down starches and fats into sugars while you chew, which is why some foods like bread and rice become sweeter when you chomp on them awhile. Another enzyme called lipase doesn’t become active until it hits the acid of your stomach, but then goes to work breaking down fats.
Compounds that help bind minerals to your teeth (which unfortunately can lead to plaque, as it will help minerals bind to bacterial films as well), promote the healthy growth of mouth tissues, and stimulate the growth of taste buds are all also in saliva.
