because the mucous is often
lost during processing.
I want to now concentrate on the gastric glands.
They are the major glands you find throughout the
wall or the mucosa of the stomach. It's
in the fundus or the body part of the
stomach predominantly. And there are
a couple of features that we need to
describe before we look at the real
histology. Again, on the right-hand side
at the top, there's a little diagram. It represents
the mucosa. It represents, first of all the
top part, there's a little pit, a little hole,
a beginning, an opening, if you like, and
that opening goes down into the gastric glands.
And the gastric gland can, or at least the
pit, can be the conveyance area, the portion
of the glands that can deliver
those secretory products from one, two, or
at least three of these gastric glands so
they combine, they unite at the top in
these pits to release their products.
And again, those glands are supported by the
muscularis mucosa. And you'll see they
extend all the way down to the level of the
muscularis mucosa. So appreciate that
generalized diagram first, then look
across to the left-hand picture.
Here, a gastric gland is illustrated, and
there are three major types of cells, and we'll
go through each of these cells in this
lecture. The surface cells are called
surface mucous cells.
They are at the surface and the initial
entry of the pit, the gastric pit.
And then you have mucous neck cells, the
next ones down. And they are at the isthmus
or they're at the level where the
gastric glands are going to branch.
As I said earlier, a number of these gastric
glands open into a common gastric pit.
That common gastric pit is lined by
mucous cells. And then you have two other
cell types. In the middle area of the gastric
pit, there are parietal cells, and
I'll describe those in a moment. Below that,
there are these blue-stained chief cells.
The parietal cell, the chief cell, and
the mucous cells at the neck and
the surface are the three major types of
cells in gastric pits. But there are also
enteroendocrine cells, cells that
secrete hormonal products. And we
don't often see this in routine histological
sections. You have to use
special stains. I'm not going to mention
this in great detail in this lecture, but
understand they exist and they have very
important functions, for instance,
secreting the hormone gastrin that has
an effect on the stomach. And the
physiologist will explain to you all
about the physiology of all these
hormonal products when you study physiology.
There is also stem cells that I will
talk to you about in a moment.
Move across to the right hand bottom part
of the slide and you'll see a
histological section now taken through the
gastric gland. Again, labelling the
various components; the pit, the
neck, and the body.
And you can see a dark-stained collection
of cells right next to the muscularis
mucosa that represent chief cells. And there
is also clusters of parietal cells
you'll see towards the middle region. In
a moment, I'm going to tell you how you
can identify each of these different cell
types. But this is just to orientate
you as to the structure of these gastric
glands before we move on. On the
left-hand side, we have our picture and our
section has been labelled. But now on
the right-hand side, we have a real section
taken through the mucosa of the stomach.
And I want you to look at that carefully.
See if you can actually
identify the mucous surface cells and the
parietal cells, and perhaps, the chief cells.
You know by now they are located at various parts,
generally, in the mucosa. There, the mucous
neck cells, clear staining. The mucous gets
lost during the processing, so the cells
would appear very clear. The parietal cells
are these red-stained areas towards the
middle of the gastric gland, and then the
chief cells, are at the base. Although, when
you look at these chief cells,
you'll also find cluttered among them some
parietal cells as well. And then underneath,
you have the very thin layer of
the muscularis mucosa also shown.
Let's concentrate on each of these cell
types now in a little bit more detail
and talk about their function. On the
left-hand side, again, is our nice helpful
diagram. The top layer of blue-stained or
blue-coloured cells represents the mucous
surface cells, mucous surface. Note the
spelling of the word mucous. That refers
to the adjective, the descriptive
term of the cells.
Mucus refers to the product, the mucous product
of the cell. So make sure you're aware of
that difference in spelling. If you look now
at the middle section, you can see
the pale-staining cells that make up the
surface of the gastric glands. And on the
far right-hand side, you can make out
the cells that make up the neck of
the glands. Here are the mucous surface cells.
Note the spelling, mucous the adjective
describing the surface cells and mucus
the product. And again, on the right-hand
side, you can see the neck cells. Now, you
should be able to observe that the mucous neck
cells are much smaller than the surface cells.
They have more prominent nuclei,
but they are smaller. And the mucous
neck cells actually secrete a
soluble type of mucus. The mucous surface
cells secrete an insoluble type of mucus.
And that's very important. That insoluble
mucus forms a layer on the surface of
those mucous cells, separating the
epithelium and the gastric glands from
the harsh environment in the lumen where
the chyme is moving a battle at time due
to the mixing activity of this stomach.
So these surface cells need to be
protected against that mechanical
abrasion. So that's the job of this very
insoluble mucus. It's a very thick
viscous type mucus. It's protective. But
there's another job that this mucus does,
this insoluble mucous does. It binds
bicarbonate. It doesn't allow bicarbonate
that's produced, into the lumen to mix
into the lumen with the chyme.
It concentrates that bicarbonate in that
insoluble mucous, and that's one of its
major jobs. And concentrating that
bicarbonate inside that insoluble mucus is
very important to stop the acid attack
on the underlying epithelium.
It's again another protective role. And the
secretion of this insoluble mucous and
the concentration of bicarbonate in that
insoluble mucous and the secretion of the
clearly watery mucus from the mucous neck
cells is controlled by the vagal nerve. The vagal
stimulation from the vagus nerve comes
down and produces the secretion of
those mucus components. And it only
happens when the stomach fills with
food and it's breaking down and mixing
food. It doesn't happen at all when the
stomach is in a resting phase. The parietal
cells, as you have seen before, are in the