renew of epithelium here. This is now higher
magnification series of three histological
sections taken through the epithelial surface
on the left hand side, taken at the base of
the crypts or glands in the middle, and also
on the right-hand side. And I want to identify
various components that are important. First
of all, the absorptive cell is called the
enterocyte. It's specialized for absorption.
It has on its surface microvilli.
When you look at the surface, you can often
see a very faint pink or red line. It indicates
all these microvilli. We call it a striated
border or a brush border. You can see it now
if you look very carefully at the apex of
the epithelium. In the central section, you
can see cells that contain a bright red product
or content. These are called paneth cells.
And the little red granules that are stained
contain antimicrobial substances that are
secreted by these paneth cells into the lumen
to combat these invading pathogens. Just between
these glandular crypts that you see here,
you can see a lot of little cells. These are
the cells in the lamina propria. The lamina
propria between the epithelial cells in
this particular section are strongly populated
by lymphocytes and cells in immune system.
On the right-hand section, you can see stem
cells. As I mentioned earlier, these glands
or these crypts, their secretory product really
are new cells to replace ones above them that
are lost at the lumen. You can see evidence of these stem cells
by seeing division. You can see the metaphase, process of mitosis,
clumped chromosomes on the equator of some of these cells as
labelled here. And these cells will divide and
finally move up along the epithelial glands
and surfaces, and do their role as enterocytes,
just like the other cells that have preceded
them and being lost at the lumen, or they
could become mucus-secreting goblet cells.
Again, on the left-hand side are the stem
cells, but there's another cell that you
can see here, an enteroendocrine cell. These
are special endocrine cells that live on their
own, embedded in the epithelium of the intestine,
here in the small intestine, and indicated.
On the right-hand side, you can see first
of all some goblet cells showing some nice
granules of mucus inside them, but more importantly,
the argentaffin cell. This is an example of
an endocrine cell, an enteroendocrine cell,
and endocrine cell within the gut.
Look very closely at that image or that section.
I think it's a lovely section because it
shows you a number of features. First of all,
have a look where the lumen of this glandular
component is. It's the white space in the
middle. Have a look at the argentaffin cell.
You can see a round nucleus. And all those
little brown granules you see are in fact
the endocrine product that this cell secrete
that have their effects in other parts of the
gut, because they diffuse into the interstitium
and into the vascular system. And that's
why they're located where they are. They
locate at the base of the cell, away from the
apex because they're not liberated into
the lumen. They're liberated into the blood
stream, underneath them in the basal surface.
So that's why you see them located there.
I think it's a wonderful description of
these endocrine cells.
Again, let's just make sure we can see the
submucosa. Previously, we are looking at the
enterocytes and the crypts in the villous
projections that come off the muscularis mucosa
and also the glandular components in those
three different sorts of folds that you
see there. But make sure you are now aware of
the submucosa. Contains lots of blood vessels.
You can see the bright red-stained red blood
cells inside some of these vessels. And as
I said before, that can move and flatten out
as the gut might swell up and become full
of chyme or food that's undergoing digestion.
It's a very mobile layer.
Also, within that submucosa, if you look very
carefully and indicated on the right-hand
side, there are ganglion cells. They form
the submucosal plexus or Meissner's plexus.
They're going to be postganglionic cells.
They are going to be innervated by preganglionic
cells that come and synapse with these postganglionic
cells you see here, and they in turn send
an axon, a process, and they bring about contraction
of the muscularis mucosa just underneath the
epithelial surfaces supporting the lamina
propria as part of the mucosa. And they make
the muscularis mucosa that contract independently
of the muscle contraction of the muscularis
externa. The muscularis externa is really
only involved with peristaltic activity to
move the food along the gut tube.
The muscularis mucosa rather contracts and relaxes
to bring about the movement of the villi,
of the mucosa, to try and increase the chance
of food mixing and coming in contact with
the absorptive surface of the enterocytes.
And here is a description or at least an identification
of the ganglion cells in the myenteric plexus
which is controlling the activity, the contractile
activity of the muscularis externa.
It's called the myenteric or Auerbach's plexus.
And again, you see ganglion cells supported by
glial cells, supportive cells. The small intestine
has three different components,