00:00
and mitochondria, of course, to provide
the energy. Let's just lastly look at the
submucosa, which is fairly uninteresting
tissue really. It's just general loose in
some areas, dense connective tissue in
other areas, containing the blood vessels
I mentioned earlier that are going to
supply the mucosa. It's that area that
can expand or contract or change its
dimensions to accommodate the increased
luminal space, during swallowing or during
increasing content of food as you would
have in the stomach. And then on the right-hand
side is the section through the
muscularis externa. The muscularis externa
here has an inner circular and
an outer longitudinal layer. You can't really
tell that from this section because you
can't see the orientation of the lumen.
But I know because I actually took the
image from the section through this stomach,
and now I know the orientation of
the lumen. So you can trust me to say, that
there is, at the top, the section
through the inner circular and the more longitudinal
layer as you can see just below that.
01:18
And then you have the serosa, the
covering, the mesothelial covering,
cuboidal squamous cells that are going
to be part of the visceral peritoneum.
01:34
That muscularis externa is controlled by a
nerve plexus, the enteric plexus that goes
all the way through the gut wall and
controls that independently of the central
nervous system. And we'll see evidence of
that as we look at other organs of the
digestive system in later lectures. It's
called Auerbach's plexus between the
muscle layers and the muscularis externa,
and the submucosal or Meissner's plexus
in this submucosa that controls the contraction
of the muscle in the muscularis
mucosa layer. Well, in summary, it's important that
you understand the wall of the gut is
composed of those layers listed there.
And I went through these layers and
explained, particularly in relation to
the stomach and the esophagus, how the mucosa
changes. And also, I pointed out the
role of the other layers in the general
function of the gut wall, particularly,
moving food along it, mixing food within
it, and then the mucosa layers
that have secretory functions, and as
we'll see later on also, absorptive
functions in other lectures. The
esophagus was specialized to pass food
through to the stomach. It's a tube, a
muscular tube that is lined by a wear
and tear epithelium.
03:10
And we learned that the stomach has a special
gastric glands within it, that secrete a
number of different components, pepsinogen,
acid, and the intrinsic factor,
that's important for the absorption of
Vitamin B12 lower down in other parts of
digestive tract. And the importance of
that mucous layer, lining the surface,
protecting the surface from the abrasion of
chyme moving about during the mixing of the
food, and also, concentrating bicarbonate
on there to protect the epithelium from
the damage of hydrochloric acid. So, I hope
you now know something about the histology
of the esophagus and the stomach. And certainly,
I hope you now understand all the
structures that comprise the wall of the gut.
So thank you very much for listening
and I hope you enjoyed this lecture.