- [Narrator] Starting with the beginning of the GI tract,
we're looking at the mouth.
And when we're in the mouth, we're dealing with teeth.
So I'm pretty sure, I'm going to probably guess,
OK, teeth are meant to chew food, meant to bite food,
tear food off, you get the idea.
But the different types of teeth, they're called incisors,
canines, pre-molars, and molars.
Now children, before they lose their baby teeth,
are going to have 20 teeth, while adults,
that means once they have lost the baby teeth and
the new ones grow in, we're talking 32 permanent teeth.
Does that mean everyone has 32 permanent teeth?
No.
That third molar, known as the wisdom tooth,
sometimes it comes in, sometimes it doesn't.
Sometimes it has to be pulled out.
So these aren't hard and cold numbers,
they don't have to be there.
It' just the typical or the average numbers.
The tongue itself, positioning the food.
Well, hopefully positioning the food while
not getting chewed on itself.
But also it's tasting the food, because the tongue
has several different types of taste buds on it.
But the tongue is more than just moving food and tasting it,
it's also dealing with speech.
Have you ever tried talking with the tongue always
at the bottom of your mouth?
Or hold the tongue to the top of your mouth.
It doesn't sound normal.
Because the tongue is going to help and shape the air
coming out of your lungs.
To make sure the air flows in the proper direction,
therefore helping the resonant sound
flow in the proper direction.
So the tongue, positioning food, tasting food,
but also speech is an important part as well.
So here you can see a picture of your lower and upper jaws.
What we're going to notice is, we have a total of
eight incisors, four on the bottom, four on the top.
These are your front teeth.
They're meant really for biting into,
for tearing things off.
Then a total of four canines,
you're going to have two on the top, two on the bottom.
These are those a little bit more pointy sharp teeth.
Canine, think of cat.
Then we have eight premolars.
The total of four on top, four on the bottom again.
These teeth are starting to get a little bit flatter,
meant more for grinding.
But the true grinding is in the molars.
And we're noticing the same 12 molars,
top and bottom, so six top, six bottom.
That's if you have the wisdom teeth.
That third molar, the one all the way to the back,
sometimes it just doesn't even come in.
So, you might have a total of eight molars,
you might have nine, 10, 11, 12, it all depends on
which molars grew in.
Genetics is what controls which ones are to come in,
and which ones don't.
So here you can see a picture of a child's mouth.
What you're noticing is, there's little tiny lines
going to deciduous teeth.
Deciduous teeth are known as baby teeth.
The permanent teeth, which you can see above it,
into the gums, are starting to push the baby teeth out.
That means the formation of the permanent teeth
are actually pushing the baby teeth out of the way
to allow them to come in.
So you have your deciduous teeth or baby teeth,
but then the permanent teeth will start to replace them
as you age.
The tooth itself is going to have two major regions,
referred to as the crown, which is what you can see,
and the root.
While the crown of the tooth, this is the natural crown,
not a crown put on by a dentist, the natural crown is
covered by this substance called enamel.
Enamel is going to be the hardest substance in your body.
But even though it's the hardest substance,
can you still wear it down?
Sure, you can still wear your teeth down.
So enamel's hard, but it must be cared for.
Below the enamel, inside the tooth is the dentin.
This helps give more structure to the tooth itself,
below that hard enamel.
Within the dentin, you're going to find the pulp cavity.
The pulp cavity has your blood vessels, it has your nerves,
and those blood vessels and nerves run down through
the root canal.
If you've ever had a hole in the enamel,
or somehow had something get into the pulp cavity,
the root canal, you'll know how painful that is to have
those bare nerves touch something.
But the entire tooth itself is held within the bone
via this periodontal membrane.
Little tiny bits of lines or ligaments help
hold the membrane and keep the tooth anchored in the bone.
But even with this periodontal membrane holding the tooth
in place, can your teeth move just a little bit?
Sure, the teeth can move just a little bit here and there,
the adult teeth.
Maybe sometime in the morning, you woke up and you
kind of closed your mouth and realized,
"Huh.
"My teeth don't quite align the right way."
That means maybe you had a lot of stress the night before,
and you were clenching and grinding your teeth overnight.
You can actually move the tooth just a little bit.
Thankfully, the tooth will usually go back to
its original position, it just takes a little bit of time.
Well, the teeth can't work alone.
We also have to look at the saliva.
The saliva is produced primarily by three main
salivary glands.
The parotid, submandibular, and sublingual.
What's in the saliva, you start with a lot of mucin.
Well mucin, it's like a mucus, but it's kind of watery.
Then we have the salivary amylase,
breaking down carbohydrates,
bicarbonate, it's a buffer, and lysozyme,
meant to get rid of bacteria.
So a lot of different things in your saliva.
So here you can see a view from the side of the head,
or a lateral view.
The parotid gland is located just below the ear.
Sublingual, well lingual refers to tongue,
so it's below the tongue, submandibular, well the mandible
is your lower jaw bone, so submandibular,
below the lower jaw.
Now once we've chewed everything up, using our teeth
and mixed it up with the saliva, we need to swallow.
Swallowing is actually a two-phase process.
You have the voluntary phase and the involuntary phase.
The voluntary phase is when you're consciously thinking
about using the tongue to push the food backwards.
What will happen is, you'll take this bolus of food,
this kind of chewed up mass of food, you'll consciously
push it backwards towards the pharynx.
The pharynx is the throat at the back of your mouth.
Well, once it's in the pharynx, then you enter
the involuntary phase.
This is simply a swallowing reflex.
What happens is, your body automatically knows
which muscles to contract, which muscles to relax,
to allow the food to go down the pharynx,
and down the esophagus.
But food is not the only thing traveling down the pharynx.
Air, what you breathe, can travel through the pharynx.
It doesn't matter if you breathe through your nose
or your mouth, both the nose and mouth connect to
the pharynx in the back.
So we have air and food passing through.
Well, somehow we need to figure out how to sort out
air from food and water.
The epiglottis is a structure that will help to sort out
and make sure that the food and water goes down
the esophagus and stomach, and the air
heads down towards the lungs.
What ends up happening is, the epiglottis is always opened
when you're breathing, but once you start to swallow
food or water, the food or water will actually push
or close the epiglottis.
That way, it prevents any of that food or water
from going down the trachea to the lungs.
So it's the actual action of swallowing that will
close the epiglottis, allowing the food and water
to head down to the stomach,
and not into the lungs, thankfully.
But once you've swallowed, and you're past the epiglottis,
you're down in the esophagus.
The esophagus will have these peristaltic contractions,
these peristaltic contractions are rhythmic.
You'll contract over and over,
about once every twelve seconds or so,
you'll go through this rhythmic contraction.
Food passes then, once it leaves the esophagus,
down through the lower esophageal sphincter.
Now I'm willing to bet you guys can probably figure out
where that is.
If you've ever swallowed something, and it was a little bit
too much, and you've felt that kind of pressure
in your chest as it slowly moved its way down?
A lot of times it happens when you're eating peanut butter
for instance, or anything else very sticky and tacky.
Well, slowly moves its way down, that's
the peristaltic contractions moving the bolus of food
down the esophagus.
Then, all of a sudden, as it moves down, down, down,
you feel it right about where your ribcage is ending,
all of a sudden the pressure disappears.
That's because the bolus of food went through
the lower esophageal sphincter,
and it entered the stomach.
The stomach is larger, there's not as much pressure
on the walls when the food enters.
So you have that lower esophageal sphincter.
It's right between the esophagus and the stomach.
Its main function, prevents backflow.
The lower esophageal sphincter is preventing
the stomach acid and the stomach contents
from coming up into the esophagus.
Because, if this sphincter's not working,
and the stomach contents are coming back up
into the esophagus, what is that?
Yeah, that's acid reflux, that's heartburn.
So your body really wants to keep that contents of
the stomach in the stomach.
So hopefully this lower esophageal sphincter
is working properly.
So here's a little diagram showing the voluntary
versus involuntary.
You start off with the tongue, pushing the food back.
Now, before swallowing, so while you're breathing,
the esophagus is normally closed.
There's no food or liquids going down there, so,
no point having it opened.
But then, once that food enters the posterior portion
of the oral cavity, the back of your mouth,
it's entered into the pharynx, and it pushes
the epiglottis closed.
Now if you notice, the epiglottis is that little
kind of blue structure sticking out
in the back of the throat.
As that green bolus of food comes down,
you can see how it pushed the epiglottis down.
By pushing the epiglottis down, it covered the trachea,
it covered the airway, so that food can only
go into the esophagus.
That's all done, because you pushed that food back,
sealed off the nasal cavity, and started to swallow.
So the food can only go one way, it can only go down.
As it keeps going down, it travels down the esophagus,
down, down, down through your peristaltic contraction.
It'll pass the lower esophageal sphincter,
and eventually enter into the stomach.
Once it enters the stomach, now we're going to start
mixing and churning it up, making sure all that
gets mixed up with the stomach acid and
the stomach enzymes.