00:01
I want to now briefly summarize the salivary
glands. On the left-hand side is a
diagram illustrating the components of
the salivary glands. You have four
processes in the diagram and they
illustrate various aspects of the
structure of the secretory portions of a
salivary gland, and then another structure
illustrating the duct portion leading from
those secretory units, and they're
labelled various names that I will refer to.
Each secretory unit of the salivary
glands are called acini. And you can see in the
diagram, and also, I will show you
in the moment on the images of the sections
through these salivary glands on
the right hand side, the acini, the
little berries or grape-shaped
collections of cells that secrete the components
of the salivary gland. It can be
classified as either mucus or serous. And each
of these acini then liberates their
products in the central space or the
luminal space of the acinus. And those
products then pass through a ductus system
that carries the secretion products
to a large excretory duct, and therefore,
into the oral cavity. That duct system
begins with the intercalated duct right
next to the acini. And that intercalated
duct then passes to the striated duct. And
those ducts are surrounded as of the
acini with myoepithelial cells that help
liberate the secretion product
into the lumen from the secretory cells, and
then move the secretion products
along the duct system, because they contract
all those myoepithelial cells.
02:08
Down the bottom on the diagram, it just
illustrates the general structures
inside the different secretory cells. And
because of the different contents,
these salivary
glands stain very differently under
some circumstances.If you now focus your
attention to right hand three histological
sections, I will point out
the difference in the different salivary glands.
The top section is the parotid gland.
02:40
When you look very carefully at the cells,
they are serous secreting, which
means they secrete a watery proteinaceous
type product. And these cells, you can
often see stain very pink. And what you're
staining there are the granules, the secretory
granules containing the salivary
enzymes in the apex stored in the
apex of the cells ready to be liberated.
The rest of the cell is often stained
basophilic, a
bluey tinge, because that reflects the
enormous factory for making the proteins
in these granules, the rough or granular
endoplasmic reticulum. On the next
section is a sublingual gland. That is
basically mucus secreting. All the cells
there are a clear bluey pale stain. And most
of the time in these glands, the mucus
product is not preserved during processing
for normal H&E sectioning and staining.
03:52
So a lot of the contents of the
cell, the secretory contents,
leak out. And so the cell appears to be
rather vacant or empty. And so you see
them rather very clear stained. And
you?ll see more of those mucus-secreting
cells in other organ systems I described
in this histology course, where
sometimes you just see whole clear cytoplasm.
04:15
And then at the bottom section is the
submandibular gland. This gland is mixed.
04:22
It has got both serous components and it has
got both mucus components. So that
enables you, when you look at histological
sections of all the salivary
glands, to distinguish between parotid,
sublingual, and submandibular.
04:43
The parotid is serous, the sublingual is
mucus predominantly, and the submandibular
is mixed.
04:53
You know, when I was a student, I could never
remember that. I still can't really,
but I have a little trick that helps me
remember which one is serous, which one
is mixed, and which one
is basically mucus. And this may sound a bit
funny but the parotid gland is the most
superior of the salivary glands, S for
superior, S for serous. And the
submandibular gland has got an M in it, M
for mixed, M for submandibular. I know that
sounds funny, but it's the only way I can
remember. And I suggest you try and think
of another way to remember it or you can use
my way. Before we move on, I want you
to go back and look at the left-hand
diagram, and I want to explain just
something about the intercalated
duct and the striated duct.
05:58
The intercalated ducts and the striated
ducts are just not conduits, at
least in serous secreting glands, because
in serous secreting glands, they
modify the secretion product. So they
have a very important role in
determining the final constituents of these
salivary glands. So in serous secreting
glands like the parotid, and we'll see later
on when we look at the pancreas in
another lecture, these intercalated ducts,
and these striated ducts are quite
prominent and reasonably easy to identify.
But they're very hard to see in
the submandibular gland, and the mucus-secreting
components are very, very short.
06:48
The mucus components of the submandibular
gland don't have very
prominent intercalated ducts or striated
ducts, whereas, the serous components will.
06:57
So often, they are very difficult to find
in the submandibular gland. In the
sublingual, you won't find it at all really
because they are so short because
they don't have any role in modifying
the secretion product.The term
striated duct refers to the fact that when
you see these ducts, they have striations
on the basal borders of the cuboidal
epithelium that forms a duct, and this
reflects very significant basal foldings
of the basal cell membrane, and
also lots of mitochondria. And this
provides a much greater surface
for the transport proteins and transport
channels to move different products
across that surface, and the
mitochondria there to of course
provide the energy for the active transport
that's required. That's why
they're called striated ducts.