00:01
The parietal cells, as you
have seen before, are in the
middle component or the middle section
of the gastric glands. They are easily
identified in H&E sections because they
have a beautiful pink-stained cytoplasm
and a nice prominent round nucleus.
Sometimes, if you look very carefully,
you'll even find these two nuclei in these
cells. They secrete hydrochloric acid,
which is a very important component that
breaks down food. They also secrete
intrinsic factor. This intrinsic factor
is extremely important because it binds
in the lumen of the stomach and also the
duodenum. It binds the Vitamin B12, and
Vitamin B12 cannot be absorbed by the
ileum, by a lower part of the small
intestine without being, first of all,
attached or combined with this
intrinsic factor. So that's an important
job of the stomach. The major role here
though in digestion is to secrete hydrochloric
acid. They are very eosinophilic.
01:17
They stain very pink, and that reflects
their affinity for eosin that's
probably the enormous number of mitochondria
in these cells. Have a look at
the diagram on the right-hand side.
01:35
And just so that I don't forget when
I'm explaining this cell structure to you,
have a look down the base of the diagram,
the base of the cell, and you'll
see there are a number of receptors there for
histamine, for acetylcholine, and for
gastrin. That means that these cells can be
stimulated or even inhibited by the
activity of other hormones such as
gastrin, and also by the activity of
cholinergic nerve fibers. So, I'm not
going to go into details of these sets.
02:14
Again, something you'll learn in your
physiology course, but I just want you to
be aware that all the cells we're going to
be looking at are influenced by both
hormones and also by components of the
autonomic nervous system. What a
wonderful looking cell this is, in reality,
even though we don't appreciate
it when we look at histological sections.
If you look at the diagram, there's two
major differences you see compared to other
cells. There's a lumen or an apical
border surrounded by microvilli which you
see in many secretory cells, but then
you have this canaliculi, these spaces,
corridor if you like, very
membranous corridors extending into the body
of the cell, the secretory canaliculi.
03:11
And then, in the cytoplasm itself are
an enormous number of these little tubular
vesicles, and again, mitochondria.
03:23
These are structural evidence that these
cells are very very important and very
active in secreting hydrochloric acid.
These canaliculi can vastly expand
with membranes because what happens
is that the tubular vesicles fuse with
the plasma or cell membrane of the
parietal cell and these canaliculi
expand greatly. And therefore, they increase
the surface area for proton
pumps that are needed to make acid. And
the mitochondria provide the energy, the high
energy requirement to have these proton
pumps working and producing the
hydrochloric acid. So that's why you see
this very specialized structure in these
parietal cells. The chief cell lies, as I
mentioned, at the base of these gastric
glands.
04:30
In the central image where the label of
the chief cell indicates the bluish
stained cluster of cells, you can also see
some parietal cells. As I mentioned
before, often, some will sneak down into
those lower ends of the gastric glands.
04:51
These chief cells secrete pepsinogen
to fairly weak lipase. And when
that pepsinogen is secreted from these
cells and moves through the gland
lumen, through the surface, it's converted
to a proteolytic enzyme pepsin by interaction
with hydrochloric acid. So that's another
role that hydrochloric acid is, has been
produced by these parietal cells.
And there are different sort of a cell,
they've got different sort of factory inside them.
Often, when the granules appear, the
zymogen granules, zymogen granules are
just enzyme precursors, when they appear
containing their pepsinogen as well,
then they would have an eosinophilic
type stain, a pinky little stain. You'd
see little red granules at the
apex of the cells. Perhaps, they're all
being released here in this section so
you don't see them. The bluey tinge, the basophilia
that you see reflects the enormous
protein factory you have in these cells
to produce the protein components of the
secretory products, the pepsinogen.
06:12
And again, at the base of the cell on the
diagram, you can see an acetylcholine receptor.
06:18
The acetylcholine receptor obviously
is there to allow the communication of
nerve fibres to this cell, or perhaps, the
interaction of hormones, etc, interacting
with receptors on this cell as well. Again,
emphasize that these cells are controlled by
both hormonal and neural input. And on the
diagram, it just summarizes what I
mentioned about having granules and also
lots and lots of endoplasmic reticulum,
and mitochondria, of course, to provide
the energy.