How Does Saliva Work?

Your saliva makes things taste great while killing bacteria and helping digestion.

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Episode Transcript

Speaker 1 (00:00):
I'm Matt, I'm Null, I'm Ben, and we are stuff
they don't want you to know. Each week we cover
the latest and strangest in fringe science, government cover ups,
allegations of the paranormal, and more. New episodes come out
every Friday on iTunes, Spotify, Google Play, in anywhere else
you get your podcasts. Welcome to brain Stuff from How

(00:24):
Stuff Works. Hey, I'm Christian Seger 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 escaping map, but it's still pretty gross.
And let's face it, we've all got saliva, so let's

(00:46):
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 mouth, moistens our food,
assists in digestion, protects our teeth, and even defends our
mouths from microorganisms. Saliva is made by a group of

(01:09):
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

(01:32):
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

(01:53):
floor of the mouth, there's these sublingual glands, which are
shaped like almonds. They produce similar loop bricating 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

(02:15):
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

(02:36):
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

(02:56):
enzyme in stimulated saliva is ammylase, used to break down
starches into simple sugars 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

(03:18):
tooth enamel is made of. We consume lots of things
with a lower pH 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

(03:40):
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 back
to your which is swallowed and destroyed in the fiery

(04:03):
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

(04:25):
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

(04:46):
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 anti microbial assassin.
In fact, spit is so good at cleaning some art
conservators use it on fragile surfaces instead of chemical solutions.

(05:11):
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

(05:35):
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 saliva, this introduces the infant to bacteria

(05:56):
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 DNA. You can

(06:17):
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,

(06:38):
illegal drugs, and HIV antibodies. Some even theorize that your
body could dispense medications automatically by modifying the salivary glands genetically.
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(06:59):
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