Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff, I'm your host Lauren volk Bomb, and today's episode is another classic from our former host, Christian Sager. Saliva lives in our mouths at all times, Controlling it as a constant battle for us podcasters. But why do we have it? And what's it made of? Christian will explain. Hey, I'm Christian Saga and welcome to brain Stuff. Most of us think of spit as being gross. I mean, it's not as nasty as the acidic bile that spews out of
a xenomorph scaping map, but it's still pretty gross. And let's face it, we've all got saliva, so let's just get used to it. Okay, how's it work? What's it for? And why do we have to swallow it? Saliva is actually an incredibly complex fluid that facilitates lots of necessary functions. It lubricates our mouths, moistens our food, assists in diggestion, protects our teeth, and even defends our mouths from microorganisms. Saliva is made by a group of cells called salivary
glands that deliver it into our mouths through ducts. Humans have four kinds of salivary glands. First, there's the parotid glands, which are opposite our front lower molars and nearly parallel to our ear lobes. These secrete a thin liquid that's full of rich antibacterial proteins and compounds that remineralize our teeth. They don't care whether you're chewing on bread or a piece of plastic, The parotids will set to work on
anything in your mouth. Next, there's the submandibular glands, which are shaped kind of like eggs and are embedded below the floor of the mouth, just above the throat. These produce a more viscous fluid used to lubricate the throat and mouth. Also below the floor of the mouth, there's these sublingual glands, which are shaped like almonds. They produce similar lubricating secretions. And finally, there's a fourth salivary gland that covers the tongue and lining of our mouths with
hundreds of smaller glands. You know how sometimes you feel small bumps on your inner lip. That's them, And while they lubricate the mouth, they also protect it against infections. Okay, so that's a lot of saliva being secreted by those four different glands. It's mostly made of water, and it also contains enzymes that break down food for digestion and do the whole protection from infection thing. When you pool all that saliva together, it's filled with minerals and proteins
that also maintain our teeth. We can basically break down saliva into two categories, stimulated and unstimulated. The stimulated kind is what comes from the parotid glands and makes up seventy of the two to three pints of saliva we generate a day. The main enzyme in stimulated saliva is ammylase, used to break down starches into simple sugar our bodies make use of. You know how when you chew on bread a sweet taste slowly emerges. That's amylase at work.
Stimulated saliva also balances the amount of acid in our mouths. Anything under a pH of four will dissolve calcium phosphate, the stuff our tooth enamel is made of. We consume lots of things with the lower phs than that, vinegar, soda, citrus, juices, and wine. You know how soda dissolves rust, Well, it would do the same thing to our teeth if it weren't for saliva. There actually isn't a lot known about unstimulated saliva because it's difficult to collect, but it's always
flowing in the background. It's pretty viscous and stringy because of a long chain of amino acids called musans. This stickiness is what lets unstimulated saliva form a protective film on the surface of our teeth. The proteins in there both remineralize the enamel of our teeth and trapped bacteria, which is swallowed and destroyed in the fiery pits of our stomach acids. Speaking of stomachs, saliva is hugely important
to our digestion. It moistens dry food, and like I mentioned earlier, it's saliva that starts breaking down starch so we can eat it. It also helps slide that food right down your esophagus and into your belly. And most importantly, saliva alters the taste of foods, making them more palatable. That's right. The bacteria in saliva is what brings out the rich flavor and wine onions, peppers, and more, and it even turns odorless compounds in fruit and vegetables into
much more aromatic chemicals called fields. Some researchers even speculate that we could use the compounds in spit to flavor food in our kitchen when it's not digesting and making things taste great. Saliva is also a lethal killer of germs. The wonder of saliva is that it's both full of bacteria and an antimicrobial sassin. In fact, spit is so good at cleaning some art conservators use it on fragile
surfaces instead of chemical solutions. This is because saliva has anti clumping properties that keep bacteria from forming colonies on our teeth and gums. Proteins called his statins not only hunt down bacteria and kill them, but also have been shown to speed up the healing process of wounds inside the mouth. Seriously, this is some wolverine style regeneration. Here, wounds that take several weeks to heal in our skin
disappear within a week in our mouth. In some cultures, a mother will even spit in her infant's mouth to teach their immune system how to produce antibodies and destroy pathogens. Because of all the antibodies already in the mother's saliva, this introduces the infant to bacteria without getting them sick. Finally, did you know that our saliva contains our entire genetic blueprint. If you're trying to get away from a crime scene, don't spit on anything because so many cells from the
inside of your cheeks slough off into saliva. It only takes half an eye dropper worth of spit to sample your d NA. You can even take a sample yourself, send it in the mail, and get your own genetic information. This includes health data like your susceptibility to certain diseases. So in the future, scientists hope to catalog every single salivary protein. It's possible that saliva could even replace blood for testing things like alcohol, illegal drugs, and HIV antibodies.
Some even theorized that your body could dispense medications automatically by modifying the salivary glands genetically. Today's episode was written by somebody on the House to Work staff, perhaps Martial Brain himself, our original host. The records have been lost to time, but it was produced by Tyler Clang. But for more on this and lots of other timeless topics, visit our home planet, How Stuff Works dot Com.