So hello, and good morning.
It's time to start talking
about the digestive system.
And we talk about
respiration and digestion
together because they are
always constantly linked.
The digestive
system is the system
that acquires and processes
our fuel in the form of carbon
Everything that we
eat except for salt
is a living cellular tissue.
And its nutrient value
rests in those polymers that
make up the bodies of our food.
Now a contrast that I want to
point out right away is that
whereas the respiratory
system structurally is like
a cul-de-sac–
you turn into the cul-de-sac,
you drive to the end,
you turn around and you
come back out the same way.
The digestive system is a
thoroughfare with an entry
end and an exit end.
And under normal circumstances,
healthy circumstances,
it's one way.
I'm going to emphasize
this, that we
eat these nutrient
materials, what we call food,
in bulk quantities.
And in order to digest
it and use it as food,
we have to break it down.
Now that includes a
combination of things.
I think the first thing I
would mention, especially
for human beings, is the
social and cultural practices
that we have
surrounding our food.
First of all, we select
food and we breed food.
We develop through materials
to be the purest form possible.
High in nutrients, high
in carbon-carbon bonds.
So that when we break them down
we get lots and lots of energy
The chemical bonds
in our food is
going to be captured in our
aerobic respiration system
and transferred to ADP.
When we phosphorylate
ADP, we make ATP.
And then we have the material
to support our metabolism.
So we're going to break it down.
We're going to first of
all select our food items.
That external business
is food science.
But then we have our onboard
material, notably our teeth,
that begin mechanical digestion.
And then the
muscular contractions
that mix and churn
those progressively
smaller and smaller bits
and the mechanical breakdown
of our food.
And what we're doing there is
increasing the surface area.
A block of food has a certain
amount of surface area.
Cut that in two,
and it has more.
Cut those in two, it has more.
As we get to smaller
and smaller particles,
the surface area goes way up.
And the reason
we're doing that is
to expose molecules throughout
that initial block of food
to chemical processing.
And that's the second step.
There are molecules that
carry lots of energy.
Such as, for example,
the polymer starch,
which is abundant in
plant food materials.
In fact, a lot of
the plant materials
we select we use because
of its high starch content.
But starch is a polymer.
Starch cannot be digested
by cells and used in aerobic
It has to be broken down
to its monomer, glucose.
And so we have
chemical enzymes that
are specific to the breakdown
of the various polymers
we've made.
So back when we talked
about carbohydrates
and we talked about starch
and cellulose and sucrose–
all of those things
have glucose content.
But we know cellulose because
of its bonding is indigestible.
But starch is loaded with
readily obtained chemical
The same thing applies
to sucrose, by the way.
Our table sugar, which we
eat in great quantities
and we actually seek out
because of the taste.
But it's a dimer, actually.
It's glucose and fructose.
We have to have an enzyme
called sucrase to break it down
into monomers, and that's
what we will digest.
And that's the second part.
Mechanical digestion is
followed by chemical digestion
to actually yield the
monomers that will
be nutrients within the body.
So if you think
about a food label
on the back of your power
bar, that food label
contains carbohydrates.
It often separately
lists sugars.
And those are in various forms.
So within that number
that's registered,
it will contain the total
content of things like starch,
things like maltose,
things like the sucrose.

And it is the monomer
content, the monosaccharides,
that our cells will use.
Likewise when we talk about a
protein content in our food,
it isn't the
protein that we will
digest or use to synthesize
our own proteins,
it is the amino acids.
And amino acids requires
some additional processing.
Amino acids release ammonia
when they're processed.
And so we have an
additional metabolic cost
to digestive proteins.
Finally we have fats.
That hydrophobic component
that is basically chemically
very, very reluctant
to mix with water.
We're going to use
that in many ways.
One of the first ways
is as phospholipid,
where the job is to aggregate
into sheets and form barriers,
like membranes.
But a second product
of eating fat
is that we will take
those fatty acid chains
and hook them to a
glycerol and produce
a triglyceride, our own
transport form which
will sustain aerobic respiration
by providing acetyl groups.
We're going to get that by a
process called beta-oxidation
of the fatty acids.
So that overview all
surrounds the fact
that human beings, like all
animals, are heterotrophs.
We are other feeders.
You can put us out
in the environment,
and the sun gives us a sunburn.
The CO2 in the air is
just an inert portion
of the air we breathe.
Whereas plants taking
water and carbon
dioxide and that
sunlight and actually
making carbon monomers
and carbon polymers as it
builds its body.
So this will give you an
idea of the system that
is meant to find, identify,
and acquire food, put
that food into our
digestive tract
and process it and free the
nutrients in monomer form.
Now from that point, the
big issue is absorption.
We're going to absorb
those monomers.
We're going to take
them into our body
and transport them
all over the body,
process them for ATP production,
yielding the energy that we
need to run our metabolism.
But also, the monomers
are the building blocks
of our own proteins, of our own
fats, and of our carbohydrate
So it's a fact we
are other feeders.
We are heterotrophs.
That tailors the
digestive system.
So what are we going to do?
We're going to break down food
into nutrient molecules that
can be absorbed
across a membrane.
We're actually extracting
them from the digestive tract.
Now the digestive tract
is not inside the body.
It is surrounded by the tissues.
But if something's in
the digestive tract,
it's actually just moving
through a hole in the body.
And you have to cross a membrane
before you enter the tissues.
We're going to deliver
these nutrients
to the cardiovascular system.
And I should add something–
to the lymph system.
It turns out that transport
of carbohydrates and transport
proteins or amino acids
occurs by directing
the root to the blood.
But fat, oils, waxes in
our diet are absorbed
not by the capillaries, but
by the lymphatic vessels,
the lacteals.
And it is the lymph
system that transports it
from the digestive tract
walls all the way up
to the top of the thorax.
And that's where
those fat components
enter into our blood flow.
Now we know that the
food contains then
two components, the
digestible component
and the indigestible component.
So basically, as we extract the
nutrients and the co-factors
and the ions that we
need for our metabolism,
we leave some things behind.
The primary thing we
leave behind is cellulose.
And cellulose is
indigestible, even though it's
made of pure glucose.
And it moves through the tracts.
Cellulose providing the
bulk, the actual structure
for our feces.
Now in addition, as this
material flows along,
the body takes
advantage of that flow
all the way along the tract
to deposit certain waste
or breakdown materials.
And those move into
the lumen and are
carried by this waste
material to the other end
for elimination.
Now notice this term.
The waste products that
leave the digestive tract.
We don't say they're excreted,
we say they're eliminated.
And that relates to this
thoroughfare, this hole
through the body.
They never actually
enter the tissue.
They basically move
through that hole
and leave out the exit point.
Contrast that with urine, where
the ammonia and urea that's
produced by digestive proteins
is actually circulating around
between the cells, moving
through the blood, processed
to urea in the liver.
And finally processed out of
the blood flow in the kidneys.
It's actually coming from
the internal part of the body
out to collection
in the bladder,
and eventually its elimination
is achieved by passing urine.
Now that's an excretion.
The digestive system– we talk
about, it's an elimination.
So we have any
number of diagrams
that can show you this.
Here's the cul-de-sac we
call the respiratory system.
Down and back.
I'd make this point–
in the air sacs,
the oxygen in the air sacs
of the respiratory system
was not actually
within the body.
When it crosses a
membrane and enters
the cardiovascular
circulatory system,
then it's inside the body.
Here is also where carbon
dioxide crosses out of the body
and back into the
respiratory system.
But the digestive system
is a thoroughfare.
In one end, out the
other, interacting
with these other
systems along the way.

Naming the parts of
the digestive tract
is a very sequential process.
It's a list in order.
Up here, the mouth
is the first cavity.
The entry protected by the
sphincter muscle and the lips.
Basically an area that
has multiple functions
in the respiratory system.
Speech and breathing all
occur in the mouth as well as
digestive activity.
But within this cavity, it is
the teeth and the tongues that
are primary digestive organs.
The tongue is a very
large and strong muscle.
It's adept.
It can move quickly to
articulate our sound
into speech.
But it is equally skillful
at maneuvering our food
so that our chewing is
efficient at breaking
it down mechanically.
So the number of times I
bite myself on the tongue
is relatively limited
to the number of times
that I eat a meal.
So from this cavity, we're going
to enter this back pharynx.
The pharynx being
the common opening
at the back of the nasal,
oral, and laryngeal cavities.
Here is where the epiglottis
manages the open airway
and basically closes it at
the instant of swallowing.
So let me make a contrast.
We breathe almost every
second of the day.
When we swallow, our airway
is closed for less than a
second as the food moves past
the glottis and its opening
to the airway and passes
down into the esophagus.
The next tube is just
a connecting tube.
And once you initiate
that swallow up here,
then autonomic
control takes over.
It is actually
involuntary peristalsis
that moves the food directly
to the stomach very rapidly.
The stomach is a bag for
the receipt of something
from the outside of the body.
And so the acid in the
stomach is going to first
largely sterilize the food.
Not completely, but largely
remove living pathogens,
kill cells, denature viral DNA–
all of those things
that we would
like to achieve before the
food passes on to a place
where the nutrients
enter the body.
Below the stomach, we
have small intestines.
Small tubes that
wiggle back and forth
have much more surface
area than large tubes
that decrease in diameter,
is in direct relationship
to that surface area, and
it's the small intestine
where most of the
absorption of our nutrients,
co-factors, vitamins,
ions, other things,
is going to occur.
But we have crudely
processing food
entering the bottom of the
tract here and entering
the large intestine.
Now oddly enough, we're
going to climb vertically
up through almost
half of the abdomen,
traverse over from
the right to left side
and descend right back down
on the left side of the body.
Then there's a wiggle.
So we had the ascending
transverse and descending
arm of the large intestines.
Often, that's associated
with the term "colon."
The sigmoid colon
will move the tube
toward the midline
and posterior of it.
So it will snake
backwards to position
over the rectum, which basically
is posterior and situated
directly above the
opening, the anus, which
allows the passage of the
elimination from the body.
We have a number of organs and
actually a number of tissues
that are in or around the organs
of that digestive pathway.
And they have a major
digestive function.
Because they have
other functions,
we don't call them primary
to the digestive system.
We call them accessory organs.
Saliva is a good example of
the many glandular functions
of the digestive tract.
Saliva is a protective
and lubricating fluid.
It has its own
digestive enzymes,
so we're going to start some
chemical digestion right up
here in the mouth.
Not oddly, we eat
so much starch.
Starch is pure glucose.
Amylase comes from the
glands in the mouth.
And we start that chemical
breakdown right here.
The liver is a large
processing organ.
Sometimes I think that
the hepatic system
should be a organ
system of its own,
because of its many
important roles.
For digestion, it produces
a substance called bile.
Bile is critical
to our digestion
because of the hydrophobic
nature of fats, oils,
and waxes.
Bile is what we call
an emulsifying agent.
It causes fats to break into
smaller and smaller and smaller
droplets and remain in that
broken down form, suspended.
That increases the surface
area and lets the enzymes that
can process fats attack them.
So we're also going to
produce bile in the liver.
By the way, we're going
to transport the bile
to this gallbladder, and
we're going to basically wait
for food to come down the pipe.
And then we're going
to squirt, squirt,
squirt as long as food
is moving through.
Storage and
concentration of the bile
in addition to the
digestive stream
is what the gallbladder does.
I want to step back
here to the liver.
We're going to use the
liver to store nutrients
in our daily feeding cycle.
So when we eat a big
meal at lunch today,
there's going to be a time
where we're actually absorbing
nutrients into the bloodstream.
The absorptive stage.
But that's over fairly quickly.
45 minutes to an
hour and 15 minutes.
Most of the usable nutrients in
that meal have been absorbed,
and now we have 3 and 1/2 or
four hours until our next meal.
So what the body does is that
during the absorptive stage,
the high stage, it stores
glucose in the liver.
It also is topping off tanks
in the muscles if necessary.
But it's storing nutrients
during the absorptive stage
in the liver.
And then as the
absorptive stage ends,
it will break that glycogen
down and feed it back
into the bloodstream
to help regulate
blood sugar in the
post-absorptive stage
until our next meal.
The final accessory organ
here is the pancreas,
the star of our generation
because of the ability
to now treat diabetes and keep
diabetics alive and healthy.
This is an exocrine gland.
It secretes many digestive
enzymes and hormones that
are important in digestion.
But the star of
the era is insulin.
The inability to produce insulin
used to be a death sentence.
If it was type 1,
insulin-dependent diabetes
used to be called childhood
diabetes or juvenile diabetes.
And it was a wasting
disease, where
a healthy nine-year-old,
10-year-old, 11-year-old
would all of a sudden
just start to lose weight
and literally would waste away.
This was despite studying
patients in all conditions,
including patients that
had unlimited medical care,
unlimited nutrition,
unlimited hygiene.
And yet they would
waste away and die.
And it turns out insulin
is a single factor needed
for the processing of
nutrients into the cells.
So insulin and its
provision now allows
us to predict a long,
healthy life for diabetes
under proper management.
And it is the pancreas
that produces that insulin.
Now let's think
about the activities.
What's actually going on
in the digestive tract?
First of all, we
do drink liquids.
Water is corrosive
as it flows, but not
so corrosive as the solid
materials of our food.
The most abrasive stuff
that we put in our body
comes into the mouth
and is processed
through the digestive tract.
So solids and liquids are
involved in the ingestion.
After we ingest and do a
few voluntary activities–
here in the top end of
the digestive tract,
we're going to
position the food,
we're going to chew it,
mix it with initial enzymes
and saliva to lubricate it.
Position that at the top of
the pharynx to the middle part
of the pharynx, where we
can hold it voluntarily
until we initiate a swallow.
So we're propelling it
voluntarily up here,
but when we initiate
that swallow,
autonomic conditions
take over and start
moving it through the track.
That's going to be the case.
Autonomic movement or
propulsion all the way
through the digestive tract
and till the elimination,
the feces, are deposited
into the rectum.
Now there is a signal when the
rectum gets full and swollen.
Stretch receptors say
it's time to eliminate,
and there is a voluntary
element to that elimination.
And mostly though to the
release of the sphincter
and the initiation of that
elimination or defecation.
So propulsion is
a second activity.
Along the way, there's
progressive and continuous
mechanical digestion.
That's the physical breakdown
of the food into nutrients.
And chemical digestion, this
is the specific enzymatic
And so we see how
specific this is
when we think about a
particular kind of food.
So carbohydrate polymers,
such as sugars and starch,
are broken down
progressively from polymers,
meaning unlimited
length of the chain,
to trisaccharides
and disaccharides,
and then eventually
to monosaccharides
that can be digested.
Now lactose intolerance
is something
that is related to lactose, the
milk sugar which is a dimer.
You have an enzyme called
lactase that breaks it down
into two monomers, and you
can digest those monitors.
If you don't have the adult
form, it stays as the dimer.
It continues to pass with
the digestive material
and produces a range
of difficulties
in your digestive tract.
Anything from mild gas
or mild indigestion,
all the way up into
vomiting or diarrhea.
So lactose
intolerance is related
to this chemical digestion step.
Likewise, we have
an enzyme called
maltase, which breaks down
what's called malt sugar,
And it's a dimer
that is broken down.
I've already mentioned sucrose.
It's broken down by sucrose.
Once this digestion
is completed,
absorption of transportable
nutrients– sometimes you
can absorb the disaccharide
even though you're
going to break it down
to monosaccharides
to use it in the cells.
That absorption
occurs principally
in the small intestine.
Although it does trail off
late in the small intestine
and in the large intestine.
We are able to extract material
from the digestive flow.
We are able to reclaim
the water in the lower
part of the digestive tract.
And our digestion in the
lower part of the tract
is also aided by an abundant
population of microorganisms,
or so-called gut flora.
Down here at the end, we
accumulate the material
that's left behind, the
indigestible material,
and eventually eliminate
it by defecation.
Now in order to control and
manage this digestive tract,
we have here a- I
think this is supposed
to be a midsagittal
section through the body,
showing the principal part
of the digestive tract.
We're going to have a tube
that varies in diameter.
The esophagus is narrow.
The stomach that
you see here high
inside the abdominal cavity–
this is the diaphragm.
This stomach is suspended
high by mesenteries,
double sheets of membrane,
a serious membrane system.
And we call this the
peritoneal membrane.
And like other double
membrane systems,
we're going to have a layer
that basically coats or lines
the outside of the organ.
Here you can see liver.
And it is basically
covered all over
by this outside red
visceral peritoneum.
It then gets to the double
fold that you see here,
producing a sheet.
Now you would see this
sheet as a webbing
sheet that stretches from the
liver down to the stomach.
This provides support
and physically
holds the stomach in position.
Now it's a flexible
membrane, like Saran wrap.
It can stretch some.
And so it provides for
flexible strength and support.
You get to the stomach and you
see the visceral peritoneum
surrounds that stomach and
forms another double sheet
like an apron that
falls down here.
Basically comes
back and starts–
this is probably
the transverse colon
or the transverse
large intestine.
Here is the mesentery again–
to an attachment point.
And it needs that attachment
point because it's
going to suspend weight below.
Notice that it moves along and
forms this rim that basically
is attached strongly
to the inner wall
of the abdominal and pelvic
cavity, shown in blue.
And that is the
parietal peritoneum,
a support structure.
Notice that there is a
space behind the peritoneum.
This is called the
retroperitoneal, or behind
the peritoneum space.
And you can see
here the pancreas
is outside the peritoneum.
Also, this is the duodenum
of the small intestine.
It loops out after the
stomach and then comes
right back into a
snake back and forth
in this lower abdomen and form
these lower small intestine
Now this particular
section has shown
you the way the serous membrane,
the peritoneum doubles.
And then when it gets to a
portion of the small intestine,
it forms that
visceral peritoneum
around each tube, each section
of the tube all the way down.
So this holds and suspends the
organs of the digestive tract.
Now the thing about
the digestive tract.
It's a tube.
To work, it has to stay open.
The muscles have to work.
If you took away that
support of the mesenteries,
it basically would
fall into a pile,
and the heavy portion would
press down and constrict
or cut off food flow.
So as we've seen before,
the actual placement
is determined by this
peritoneal cavity.

We see that another section that
shows you that continuation.
Notice that the rectum
here and the uterus
in this female section.
The urinary bladder
in both sexes
are both below the peritoneum.
And the suspension of
the small intestine.
Here is the sigmoid colon
coming over the rectum.
The small intestine.
The transverse
colon you'll notice
in this anterior position
in the stomach above it.
The liver located above that,
right below the diaphragm.
Here is the pancreas
and the duodenum.
The first– let's just
say the first six, seven
inches of the small intestine,
which has looped out
into the retroperitoneal space
that enters right back in
to join with the
lower small intestine.
When we look at the wall
of the digestive tract,
we see a very sequential
and very logical
ordering of the
membrane, starting
with the serous membrane.
What we call the serosa.
We see outside a connective
tissue layer and the peritoneum
Now here you can
see this mesentery
and its sheet-like form.
See how when it's wrapping
this portion of the tube,
it also provides not just
this flexible sheet that
suspends the whole tube, keeps
it from dropping into a pile,
but also provides
structural supports
for the tube-like structures
of the blood vessels,
arteries, and veins.
And the nerve, shown
here in yellow.
Because yellow nerves have
to penetrate several layers
of this digestive tract.
So you'll notice
how they come here
between the muscles,
two muscular layers that
form the muscularis,
and they fan out
to provide the neuromuscular
junction that can stimulate
autonomic contraction and
relaxation as we produce
these muscular waves
called peristalsis.
Now when you have
two layers like this,
the layers are defined by
the way the smooth muscle
cells are laid down.
So the outer one is called
longitudinal because–
showing the pointer running
in a longitudinal way.
They run along the
length of the tube.
So when the longitudinal
muscle contracts,
the tube gets shorter.
Inside is a circular
layer so that the muscles
are laid down as a
circumference at that position.
So the circular muscle layer,
when you contract that,
the tube decreases
in diameter, and it
pushes the non-contracted
material in either side
away from it.
So it gets thinner
and longer when
the circular muscle contracts.
Now these nerves,
blood vessels are
going to permeate
this entire structure.
Even though they're not drawn
in at this magnification,
they are providing
supplies and nerve services
to all living cells
in this system.
You'll notice that
the nerve extends
beyond the muscular layer
to this next submucosa.
Mucosa is going to refer
to mucus production.
And since the mucus
production is actually
occurring in this inner part,
we're going to see this,
called the mucosa, surrounded
by the submucosa, shown in blue.
You'll notice there is a
nerve net or a reticulum that
basically spans between
the circular muscle
and the submucosa.
We can see the present of
glands in the submucosa that
are producing the
secretions that
are added at a particular
part of the digestive tract.
You can bet that there's plenty
of mucus all the way through.
Finally, this mucosa,
showing you the ducts here
from a gland in the submucosa,
contains these green spots.
These are lymph
nodules that are placed
in the digestive tract, the
so-called MALT, or Mucosa
Associated Lymphoid Tissue.
Now let's make that
connection to that name,
MALT. Every tract in the body
that opens to the outside
has mucous glands.
We call them goblet cells.
And that is because we have to
moisten and line that tract.
Things may be moving in and out.
They may be moving–
like in the respiratory
tract, the mucus escalator
brings that mucus
and dirt back up
to where we can put it
in the digestive tract
and move it along.
The digestive tract
moves through.
Urine moves through.
There's a lubrication
that's necessary for
reproductive function as well.
And so this mucosa is
equipped with nodules
that allow for the
aggregation of lymphatic cells
and other leukocytes.
Any time you have a tract
that is moving material
from the outside to the
inside and the digestive tract
is going to have a major portion
where there's absorption,
there's the danger of
contamination or infection.
So the presence of MALT, Mucosa
Associated Lymphoid Tissue,
is logical here in
the digestive tract.
We also have
another abbreviation
that goes right with that called
SALT, Skin Associated Lymphoid
And the connection is obvious.
The skin faces the outside.
And so the chance of
infection or contamination
is reduced by the dry and
impermeable nature of the skin.
But some things
still do get through.
And so having a lymphoid
tissue distributed
in the skin as an element of
the skin, again, it makes sense.

MALT is shown here.
Mucosa Associated
Lymphoid Tissue.

Entry into the GI tract.
Let's start the trip.

In the GI tract, in the oral
cavity, or buccal cavity,
this is where we have our
voluntary or perceptible
special sense.
And that is taste.
Taste helps us a great deal,
because we can taste things,
like materials
that are the basic.
pH bases are very
deadly themselves.
And when we put them in our
mouth, they are very bitter,
and we spit them out.
We don't swallow.
We also can detect
the purification
that occurs when food
substances break down.
They become spoiled.
They produce acid.
They taste sour.
They taste just unpleasant
because of the combination
of chemicals.
So taste sensation is
a part of this cavity.
Mechanical digestion is what
we're going to do in spades.
Now we've already
selected food substances.
We prepare those
food substances.
We soften them.
We precipitate protein
through chemical treatment.
So for example, think
about what pickling is.
Think about when we make jelly
or we preserve things in sugar.
What we're doing is
processing the food
to be more digestible
and often more appealing.
We also sit down at the table
after the kitchen tools,
cooking, and the
knives, the ladles
have basically chopped our food
into small bits for us prior
to putting it in your mouth.
But when we put it in our mouth,
we're going to position it,
and we're going to
cut it with our teeth.
The teeth are a
voluntary activity.
We can chew our food well,
as our mother suggested.
And during that process,
mucus and saliva
is being mixed with the food.
Also, the glands in the mouth
produce salivary amylase.
"Am" refers to starch, and
"lase" means to break down.

Starch is very accessible
and very abundant.
Flour is largely starch.
Sugar is largely starch.
And so these
digestions are released
by the richness of
our diet, and starting
the digestion in the mouth,
breaking it down to glucose,
is logical.
Though we're putting
material in our mouth
and as thoroughly as we
cook it, as carefully
as we select it, just carrying
it from the stove to the table
is going to get some
potential pathogens.
Some debris on it.
So in the mouth, we're going to
see the addition of lysozyme,
an antimicrobial
agent, and antibodies
that are present to begin
the cleaning up of our food.
Now mentioning,
again, a reminder.
Respiration and speech are also
important in the oral cavity.
But normally when we're chewing,
we don't use our airflow.
We can breathe while we chew
by using the nasal cavity.
But we do that largely by
shutting the oral cavity off.
And don't speak with your mouth
full is a good indication.
It can lead to choking, but
it also garbles your speech.

This cavity is one
that is the mandible,
and the maxilla provide
the mounting depressions
for the individual teeth.
They are surrounded
by soft tissue.
The tongue in the base
and a bilateral division
as we see these tissue
sheets called the frenulum.
The labial frenulum here at
the lip joining at the midline.
The lingual frenulum
below the tongue.
And opening to the
ducts of the glands
that provides saliva and
mucus and other substances
in the mouth.
This midline section,
midsagittal section,
is meant to give you a
different view of the separation
of this nasal cavity.
We talked about the hard palate.
Here's the palatine bone back
here and the palatine process
at the maxilla here.
The teeth shown only
in the incisor region
in cross-section.
But the surrounding of the other
teeth and back to the molars
shown on the right side.
The body of the tongue is
extensive and its basic
connection here to the inner
portion of the mandible.
And the positioning of the
hyoid bone showing you,
I think in the
best way possible,
how the hyoid interacts
especially with this larynx.
See how it is tied
to the epiglottis?
And then it forms a U
so it would come out
toward the pointer
and curve back
in this direction to surround,
in this case, the left side
of the trachea.
But the main thing
about this that's useful
is the positioning of these
tonsils and salivary glands
that are shown.
And the joining of the
pharynx, the nasopharynx, which
is normally open for breathing.
The airway's open
almost all the time.
And this flap right
here, called the uvula,
that part that you
see sticking down
when you look in the
back of someone's throat,
is a mobile flap
that can actually
move up and separate the
nasopharynx from the oropharynx
This is important
when you swallow.
When you're pushing
that food back,
you just contract
muscles and this is open.
We would squirt that food right
back up into the nasal cavity.
But the uvula can seal that off
as you're positioning the food
here in the oropharynx.
Now at that positioning,
even through positioning
and holding, you can
breathe around that.
But when you move
this food down,
there's the danger that
it will enter the airway.
This is where the epiglottis
is going to flop down
and the esophagus
and the oropharynx
are actually going to bulge.
It's going to basically move
over in this like a roof
and drop off the eve
on the other side
as the food enters
the esophagus.
We do see tonsils, which are
fancy kind of limp nodes.
And their size and
their susceptibility
to infection or
response to infection
are well known in
children, especially.
Before there was a
lot of immune cells.
We do have the presence
of these tonsils.
And tonsillitis is a
common childhood disease.
In my youth, tonsils
were simply removed
after the third or fourth
case of tonsillitis.
Now the medical tendency
is to retain them
and to keep them for
their protective value.
Salivary glands make
quite a bit of saliva–
1 and 1/2 liters.
That's almost two quarts.
It contains a water
base, mucus, proteins,
and the additional
digestive enzymes.
Now these are just
the initial enzymes.
They are not the full suite.
But we do get some
substantial chemical
digestion of those easily freed
up nutrients in the mouth.
It's important to
lubricate the food.
If you think about
food, even if it's
in its condition of being
cooked or being prepared,
we often add oil, we often
break down the watery substance.
And the breakdown
of the food material
produces a slick material.
But we're going to have
to constantly lubricate
that to keep it moving.
Because if it's dry, it's
unlubricated, it will stick.
Dissolved substances
provide the taste.
And taste has become an element
of our enjoyment of life
rather than our primary
protective mechanism now.
But all of that's
going on in the mouth.
Taste buds are an
interesting consideration
because the tongue has
contradictory functions.
It's handling the
abrasive material
and it's pushing it around.
It's pushing it around
and rubbing that material
and moving it, meaning
that the most wear that's
encountered in the
digestive tract
is right there on the surface
of the tongue before all
that lubrication [INAUDIBLE].
Now to look at it in a
little different way,
the sense that we
call taste requires
a very delicate membrane and
the binding of chemoreceptors.
So it's not likely
we're going to stick
those chemoreceptors straight
up on the surface of the tongue.
And in fact, we don't.
What we do is produce
these bumps called
papilla and these depressions.
This is called the
moat of the taste bud.
We're going to take the
sensory cells shown here,
and we're going to line the
vertical surfaces of the moat.
You can see it here.
Here's the moat.
And here is the taste bud.
This is a chemoreceptor.
And these exposed
membrane-binding materials
will bind to one and only
one kind of chemical.
So when we say it's
sweet, sour, bitter–
what do we say, sweet,
sour, bitter, meaty–
there's one I've left out,
I'll get it in a moment.
That's because the specific
receptors in that region
only respond to that kind
of chemical in the food.
It is the dissolved
material that is
producing our sense of taste.
That's why sweet
and salt and acid.
Acid is sour, and–
I'm sorry, bitter is base.
And then umami is
more complex, but it
is the dissolved material
for meaty substances.
Salivary glands.
I went the wrong way, didn't I?

The salivary glands
are shown here.
They're massive.
The parotid right
in front of the ear.
The submandibular below
the jaw and the sublingual
pump out large quantities,
especially during eating.
Now saliva is an
important sense of our–
part of our health.
Our mouth should be fairly
lubricated and moist
at all times.
Dry mouth is
something that changes
the conditions of
the mouth and makes
you susceptible to
everything, from tooth decay,
to other types of infection.
Salivary glands can
also be infected.
This is a case, something
you probably have never seen.
This is a child with the mumps.
The salivary glands have been
infected by the mumps virus,
and they swell.
The entire neck swells up.
It aches.
It's very sensitive
to temperature.
It's sensitive to touch.
I know that when mumps
occur, generally it's
a debilitating disease, that
the child just feels very bad,
not moving around.
But in general in
children, at that stage
of the development,
the lymphatic system,
there is not a
substantial danger.
However, if you
survive childhood
without contracting the
mumps or being vaccinated
and contract it
as an older adult,
it can move through
the glands of the body
below the base of the neck.
And especially in
males in the testes,
it can provide a disease episode
that will sterilize the male.
So in adults, it is a
more dangerous disease.
Teeth are a story in their own.
It's why we have a medical
practice called dentistry,
which is specializing in teeth.
This just illustrates
the variety,
the plasticity between
different species
and how teeth have adapted.
Because it turns out that
teeth are the onboard tools
of non-human animals.
They are their
main and often only
kind of mechanical digestion.
So snakes have no arms.
See how the teeth
point backwards?
This lower jaw can
move forward and pull,
and then the upper jaw
can move forward and pull.
And those teeth
basically are the hands
that push the prey
item into the throat.
The dog has shearing
teeth, is a meat eater,
and killing teeth
here, the canines,
named after the dog
that reflect its diet.
Deer are herbivores, so
here are the snippers.
And then we move the grass.
Grass has a lot of nutrition.
But that grass must,
absolutely must be ground fine.
You have to break
enough of the cell walls
that you can squash the
membrane cell inside and release
the nutrients.
So big flat molars in
long rows and a large jaw.
So what you see in deer and
in cows and other grazers.
The beaver uses its front teeth
better than an [INAUDIBLE]..
It basically can chew
through a tree trunk.
If you keep the beaver in a
zoo, you have to give it wood.
You have to replace
wood for it to chew,
or its teeth basically
will grow to the point
where it injures itself.
The elephant's canines
have reversed and come
outside as what we call tusks.
These are used in everything
from sexual display in contest
to digging holes
in dry riverbeds
to reveal a surface of water.
Finally, humans.
Because of social,
cultural factors,
our teeth and jaws
have been much reduced.
Our jaw is shortened so that we
have a flat face at maturity.
I would point out that
our close relatives,
like chimps and gorillas, have
that protruding mouth and jaw.
It comes out here,
all the way out here.
And the reason for that is more
jaw space, more chewing space,
because they're
eating raw leaves.
Raw plants all the time.
We do so much food selection and
food processing with our tools
and softening with our cooking,
that these teeth are adequate.
And I think that they
have taken basically
the selective
pressure off of teeth
and made them
something that can move
into a new realm in
the same way our food–
we care more now about the
taste than the nutrient value.
We know we'll get
enough calories.
And with our teeth
often, we care more
about the appearance
of the teeth
than we do about
their actual function.
We have two sets of teeth
determined by genetics.
Another animal that has the
same thing is elephants.
So that these small teeth,
the deciduous teeth,
will develop as
the jaw, mandible,
and maxilla as they grow.
And the replacement,
the size of the teeth
will match the size of the
jaw and the emergence–
notice when these come in–
will match the
development of the jaw.
They come in when
there's enough room.
Now as the jaw continues to
grow to this larger and larger
structure, we
replace these teeth
on an alternating
schedule, forward and back,
forward and back, with the
third molars and wisdom
teeth being the last ones
as the jaw elongates.
This bicuspid
organization is one
that provides us with our
permanent set of teeth.
And in fact, we now have good
enough dental care and hygiene,
and the fluoridation of water–
all of those contribute to very
long-lasting dental health.
An important element
of our health.
And we also have
prosthetic substitutes
so that we can produce teeth
that are artificial teeth that
function well in our feeding.
The tooth itself has
a bony structure dent
and is more like bone.
Enamel is a shell exudate
that hardens and protects
the outside of the tooth.
I would point out enamel is the
hardest substance in the body,
harder even than bone.
The tooth is secured
into a socket
with a cement layer attached
into strong collagen
fibers, the so-called
periodontal ligament.
Notice the two-root structure
that increases the surface area
by having two roots and also by
allowing them to descend deep
into the bony socket, the
so-called alveolar process
of the mandible or maxilla.
We're going to provide the
material for good tooth health
through the delivery of
resources in the blood arteries
in and veins out,
and we're also going
to make the teeth sensitive
by the presence of nerves
within this so-called pulp
cavity, where the living
cells are polymerizing
both of these materials.
Seal it with a fleshy
growth, the gingiva, or gums.
And the tooth is complete.
It is these gaps,
it is the contact
point between the teeth
where food is lodged,
and if not cleaned out, attracts
increasing levels of bacteria.
Those bacteria can
damage the tooth
by producing dental caries.
Here is a micrograph of the
bacteria and an extended or a–

not extensive, but advanced
state of bacterial growth.
In fact, the bacteria
you notice here
are diverse in their
shape and their identity,
and they produce an actual
layer, called dental plaque.
Now a clean tooth
surface will only
host certain number of bacteria.
If you allow this plaque or
these biofilms to develop,
it produces a new
environment, including
anaerobic environments.
And new bacteria are recruited
just by breathing and eating.
These bacteria can have
a bad effect on the teeth
and cause chemical reactions
like the production of tartar
and calculus, which
are hardened plaques
and definitely indicate
an advanced state
of bacterial growth.
Tooth decay will
progress, showing
erosion of the
surfaces, showing splits
developing within the enamel.
Infected gums, as
shown here, will
begin to recede and
produce these pockets.
This is a very badly
affected and infected mouth.
Periodontal disease
can lead to the loss
of teeth, receding gums,
and other problems.
That's very interesting,
because when
we live our lives
in a certain way,
we figure humans have
always done that.
Well it turns out,
they have not.
We have not had refined
sugar in such high amounts
throughout the history
of the human being
and its populations.
What we see is
that when we start
to introduce unlimited
amount of sugar
and we start to feed on that
sugar in unrestrained ways,
that the amount of tooth
decay is shown by examining
the teeth in grave goods.
The amount of tooth
decay goes way up.
It's basically a sugary
treat is like painting
syrup on your teeth,
which is a perfect medium
for bacterial growth.
You think about your mouth,
most of the time, it is dark.
It is moist.
And it is warm.
Add sugar, and it's a perfect
place for bacteria to grow.
If you, however,
take a sugary snack
and clean up immediately,
clean the surfaces
and clean the gaps, that
can control this factor.
Floss is underrated in that the
contact points and especially
the junctions between
the guns and the teeth
are especially
susceptible to decay.
And so floss actually
improves your prospect
of good dental health in a
great– in a large degree.
Now we've been at
this about an hour.
So what I'm going
to do is I'm going
to end the first part of the
show and take a short break.
And we will return.

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