00:01
Now there are different ways in which exocrine
glands are named or classified. First of all,
if you look at the epithelial surface shown
on the left-hand slide, the image of an epithelium
in the gut, you can see single glands or single
secretory cells called goblet cells that look
like a wine goblet. They are shaped like a
wine goblet and these are called goblet cells.
00:33
They secrete mucous. There are examples of
a unicellular gland, a single cell sitting
in an epithelial surface or on its own. Or
there are clusters of these cells all the
way along the epithelial surface. If you look
at the image on the right-hand side, this
is an example of a multicellular gland. Here
is a sheet of epithelial cells that are secretory,
forming a number of layers. And if you look
very carefully at this stomach mucosa, these
layers of epithelial secretory cells, you can
see that they stain differently.
01:16
The surface ones are very clear staining. In the middle,
you can see some cells that have a pink, reddish
stain and down the base of these epithelial
layers of cells, you can see bluish stained
cells. And that indicates that in this sheet
of secretory epithelial cells, there are three
different sources of secretory products. So
that is an example of a multicellular gland.
01:50
Now I want you to remember the word mucosa,
that I have shown you on the slides, stomach
mucosa. The word mucosa is a word or term
I am going to use in a number of lectures,
particularly when we look at the organ system.
So please remember that word because later
on towards the end of the lecture, I am going
to explain what a mucosa is. I won't do
it now because it is more important and more
appropriate towards the end, but just remember
that word mucosa. Okay, these multicellular
glands can get far more complex than just
a sheet of cells you saw in that stomach mucosa.
They can acquire a duct rather than secreting
onto the surface like a goblet cell or like
these cells in the stomach mucosa during development.
02:43
When the epithelium invaginates into the underlying
lamina propria, the portion that connects
the invaginated epithelial cells to the surface
is retained, and that forms a conduit or a
duct. The deeper epithelial cells that have
invaginated into the lamina propria become
the secretory cells, the busy cells that make
the secretion products. And so we can further
classify multicellular glands that're having
ducts. And if the ducts don't branch, we call
it a simple gland. But if the duct branches
like you see in the three diagrams done in
the bottom of this slide, we call it a compound
gland. Now the classification can go further
if you look at the nature or the shape or
the structure of the secretory product and
I am not going to go through the names listed
here and I certainly do not want to emphasize
these names or I certainly would not expect
you to be able to recall these names, because
in reality when you look at sections through
multicellular glands, it is very difficult
to appreciate the three-dimensional structure
and therefore we have to name the glands like
you see listed here. It is very different
though to needing to remember the why and
which epithelia are named and classified.