In the last part of this
unit, we took a look
at the full GI tract.
Now let's start taking a
look at the accessory organs.
We'll start by taking
a look at the function
of the salivary glands.
So here's an image of where you
find all the salivary glands.
As you can see, there are
actually three major salivary
There's the parotid gland, which
secretes saliva into the mouth
through the parotid duct.
There's the submandibular
gland and associated duct.
Submandibular referring to
below the mandible bone, the jaw
And then we have the
sublingual gland, which
is found below the tongue.
The salivary glands are exocrine
glands that secrete saliva,
which is a watery
fluid that contains
mucus and one digestive
enzyme that we'll
look at closely later,
salivary amylase.
Ultimately, saliva's role is
to moisten food and thereby
facilitate the mixing in
of the salivary amylase,
and also to promote and
facilitate swallowing.

The liver is another
accessory organ
that we've looked at previously,
but only very quickly.
As we mentioned, it's
attached to the duodenum
via the common bile duct as
indicated in the image here.
However, before it ever
gets to the small intestine,
the liver is connected
via the hepatic duct
to the cystic duct.
The cystic duct is attached
to the gallbladder.

There are many
functions to the liver.
The liver is involved in the
synthesis of plasma proteins
found in the blood.
The liver also stores
many substances,
glucose in the form of glycogen
and fat soluble vitamins.
It also plays a role
in detoxification.
It helps to detoxify drugs
and other harmful substances.
It breaks down these
toxic substances
into items that could be
more easily eliminated
from the body via the kidneys.
It also plays a
role in excretion.
The liver excretes many
substances, bilirubin,
cholesterol, and drugs.

It plays a role,
as we mentioned,
in metabolism of
carbohydrates, but also
in metabolism of protein,
and metabolism of fats.

It also plays an important
role in fat digestion
by synthesizing bile
salts and releasing bile.
We'll talk about bile and a
little bit in terms of the role
it plays in digestion.
But what happens is the
liver produces bile,
and then it secretes it
into the hepatic ducts.
The hepatic ducts connect
to the cystic duct,
which leads to the gallbladder.
As a liver produces
more and more bile,
it gets stored in
the gallbladder.
The gallbladder fills with bile,
and it doesn't release the bile
until food after coming
down into the stomach
and starting the
digestive process that
occurs there, is released
into the small intestine.
When the food is released
into the small intestine,
the gallbladder actually
contracts, squeezing bile
down through the
common bile duct
into the duodenum, that starting
portion of the small intestine.

The reason I show this
portion of the image
here is to show
that the liver has
a lot of lymphatic and blood
vessels traveling through it.
Because as mentioned already,
it plays a major role
in terms of breaking
down chemicals
that get into the body.
When we eat food
and the nutrients
are being absorbed
into the blood
as we saw in previous videos,
all those blood vessels
from the small and
large intestine
first traveled to
the liver in order
to remove any chemicals that
ought not to get into our body,
or to process those chemicals
to be converted into chemicals
our bodies actually can use.
In this region shown here, we
can see that the common bile
duct actually connects with
the pancreatic duct at a place
called the ampulla vater.
At the ampulla vater, there's
the sphincter of oddi.
The sphincter of oddi
stays contracted again
until food moves out
into the small intestine
from the stomach.
And then the sphincter of oddi
relaxes as the gallbladder
contracts, allowing the
digestive enzymes as well
as the bile to move out into
the chyme as it flows through.
So I mentioned we'd
talk about the role
that bile plays in digestion.
Ultimately, bile
is not an enzyme.
It does not play a
role in breaking down
the food chemically.
But it does play a role
in helping to process fat.

If you think about
a food that we eat,
there's proteins, and
carbohydrates, nucleic acids,
but there's also fats.
Most of the digestive
fluids that we've
been talking about so far
are made up of mostly water.
As you may know already, fats
and water, lipids and water,
don't mix.
If you remember playing as
a kid with oil and water,
when you poured the
oil in the water
it just floated on the surface.
It didn't actually mix together.
Well if we're eating
food with fat in it,
and most of the fluids that
we have within our body
are made of water, how do we
actually break down that fat?
Bile plays that
role in digestion.
Bile is a chemical that
when it mixes in with fat
allows for fat to
dissolve within water.
So as chyme is being
released from the stomach,
the fats are not fully mixed
in with the watery component
of the chyme.
But then bile is immediately
released from the gallbladder
into the duodenum to
mix in with that chyme
and allow the fats to actually
mix in with the water portion.
Later on we'll see, then,
that the pancreas then
secretes enzymes that can
actually break down the fat now
that it's mixed
in with the water.
The function of the gallbladder
has been spoken about already.
Ultimately, the
gallbladder stores bile
that has been
produced in the liver
until it's an appropriate
time for it to be released,
because chyme has
left the stomach
and moved into the duodenum.

So what role does the
pancreas play in digestion?
Ultimately, the
pancreas has a number
of chemicals that we'll take
a look at in a minute that
are produced and then secreted
along the pancreatic duct,
again into the duodenum
in this region here.
We've discussed the
pancreas before,
because it also plays a
role in endocrine function.
Endocrine functions
occur when the pancreas
is releasing insulin or
glucagon into the blood
to help control
blood sugar levels.
However, in this case, we're
dealing with exocrine function,
the pancreas is
secreting out ducts
into the small
intestine to allow
for the digestion of food.
The pancreas also
releases bicarbonate,
which is basic chemically.
The reason it
releases this base is
because the stomach has released
hydrochloric acid to mix
in with the chyme inside it.
The bicarbonate is released
from the pancreas in order
to neutralize that
acid so that it
doesn't damage the intestines.

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