HSCI 4590 Histology- general histology of the stomach (AP 4:40)

Hey y’all. Dr. Brown back again with
another thrilling video, this time about the histology of the stomach. So just in
case you haven’t had Anatomy, or you haven’t had Anatomy in a hot minute, just
a reminder of the stomach is this pouch like extension of the alimentary canal.
and it’s located kind of to…mostly to the left of the midline and the superior
portion of the abdominal cavity, and the stomach can be divided into four primary
distinct regions. So we have the cardia or cardiac region; that is the region
where the esophagus meets the stomach. We have the fundus, which is the superior
kind of distinction of the stomach, and you’ll find that there are other organs
that have kind of a superior hump on them called a fundus. And then the main
part of the body…sorry…the main part of the stomach is called the body. So we see
that right here, and then this is divided into the two parts of the pylorus. So the
pyloric Antrim and pyloric canal are both parts of the pylorus or pyloric
region of the stomach, and that’s simply where it narrows down as it meets the
proximal most portion of the small intestine. Histologically, the stomach is
very different from any of the other primary digestive organs. So what we’re
gonna do is look at a cartoon of stomach histology first, and kind of go over the
the general features, and then we’ll actually look at real micrographs and
see how those four layers and it’s actually not all four, but two of them in
particular are modified to enable the stomach to do its job of chemical and
mechanical digestion of swallowed food. So the first thing you’ll notice about
the mucosa of the stomach is that the epithelium and the lamina propria are
not in a nice kind of wavy single layer like we saw in the esophagus. Instead the
epithelium and lamina propria of the mucosa are invaginated or pulled
downward into kind of a pocket, so that you can see up here at the surface we
have these kind of holes, and then in cross-section we can see these holes
lead down into this invagination of the epithelium. So most of
epithelial surface area is not exposed to the lumen of the stomach, which is
full of gastric juice, and gastric juice is this combination of primarily
hydrochloric acid, very powerful digestive enzymes, and mucus. I like to
call it murder juice; it’s got a pH of anywhere from 1 to 3 and it contains
very powerful protein…proteases, and I don’t know if you guys have checked but
you’re kind of made out of proteins. So a lot of the modifications we’re gonna see
in the mucosa are a trade-off between needing to make these substances that
can digest meat, and dealing with the fact that we’re made out of meat, and
therefore could be digested with these things. And so the first kind of
adaptation to that is the folding inward of the gastric epithelium into these
gastric pits up here, and in the gastric glands which are what line these
invaginations of the epithelium. Up at the top of the gastric pit you’ll see
it’s largely covered with surface epithelial cells, and the surface
epithelial cells are primarily mucous secreting cells. So there’s always gonna
be kind a, a thin layer of protective mucus covering the parts of the stomach
that are actually coming into contact with the gastric juice. As we move down
into the gastric glands, we see some of the cells that actually produce the
gastric huge…gastric juice. I can’t say words. So the first of these is the
parietal cell seen here. These cells are very large they tend to stain red in standard histological preparations, and these are the cells that are producing both the hydrochloric acid and a substance called intrinsic factor,
which is necessary for the absorption of vitamin b12. Then on down we have our
chief cells, and these contain little granules called zymogen granules, and the zymogen granules are going to become active protease enzymes once they reach
the acidic environment of the lumen. Right? We keep them inactive until we get out of here, and up into here where we have some protection
from that gastric juice. Then the acid in the gastric juice can…can turn…can turn
the zymogen into enzymes such as pepsin, and then finally down here in the bottom
part of these gastric glands we see some entero endocrine cells now these are
also often called G cells and they’re called that because entero endocrine
means they’re creating digestive hormones and the hormone that’s produced
most often of the most well well-known initially was gastrin so these are
gastrin secreting cells so they’re also called G cells we now know in fact that
they’re also secreting the hormone somatostatin so in taro endocrine cell
is a more appropriate name for them all right we’ve seen it in a cartoon now
let’s actually see these things in real life let’s look at some actual
histological preparations so here we can see a very low mag image of the stomach
but we can already make out some of those distinctive features that I
mentioned in the last picture so here we can see the gastric pits right and you
notice these surface epithelial cells have a very distinct appearance they are
essentially goblet cells these are columnar mucous secreting cells and
they’re going to be making the mucus layer that’s going to protect everything
up here as we move downward into the gastric glands we see some cells known
as mucus neck cells so these little patches of darker cells down here and
here they’re kind of small and very dark staining they’re very basal philic and
these little guys are going to be producing more mucus and they’re going
to be protecting the more delicate tissues further down in the gastric
glands so here you can see a gastric gland coming down so just outline this
little gastric gland as we come down now keep in mind these are three-dimensional
structures so you see it appears to end here and that’s probably because we’re
looking at a two-dimensional section and part of it either went away from us or
toward us now you can also see as you move downward so from the surface of the
mucosa deeper down toward the lamina propria that the epithelial cells appear
to change color and that’s because the
parietal cells this is mostly in here parietal cell these tend to be more es
NF philic so there are red or color and then the chief cells lower down are
going to be more purpley or blue so we can kind of see this trend even at this
low mag image but let’s go up in magnification and look even closer at
these gastric glands so in this higher magnification image we can see the
distinctive surface epithelial cells up at the top and I’m probably going to
need a different color pen than red for this so let’s go ahead and switch to
we’ll go back to black poop and then as we move downward we can see some of the
mucous neck cells down in here and then we very distinctly see the parietal
cells so you know these guys are parietal cells they’re large they’re red
they tend to be pretty round you can see they’re they’re fairly circular in shape
and further down still we see the blue chief cells so if you get a really good
section at a good magnification it’s not really hard to distinguish between the
parietal cells higher up in the gastric glands and the chief cells lower down in
the gastric glands what is hard to see in a typical stomach is the entero
endocrine cells and that’s because they’re fairly rare so if we look closer
we can see a very distinct parietal cell here with its characteristic central
nucleus and red or pink staining and then we can also see a couple of chief
cells right here and you notice that they tend to be more columnar cells
their nuclei tend to be more basal down toward the bottom of the cell and of
course they stain more purple or blue you still can’t see any entero endocrine
cells in here like I said they’re kind of hard to spot so what we’re gonna do
is cheat a little bit this is a section through a stomach with somebody who has
I think it’s called G cell sarcoma but it’s cancer where you produce too
many Antero endocrine cells so since this person has essentially G cell
cancer we can see a G cell here I’m going to switch back to red so it’s
easier to see so these large kind of distended cells with the centrally
located nuclei but they’re not parietal cells they
don’t they’re they’re not red in color these are the entero endocrine cells so
like I said these are harder to find unless you have a patient with G cell
cancer next we’re gonna look at the other layer that’s heavily modified so
we’ve seen so far how the mucosa is modified with it’s in folded epithelium
and lamina propria with the stratification of the cells so that we
have the surface epithelial cells and the mucous neck cells closer to the
caustic environment of the gastric juice then the parietal cells making the
hydrochloric acid and then the chief cells even further down making the
zymogen granules which don’t become active until they hit the hydrochloric
acid which is going to be higher up so this is going to protect our underlying
tissues the lamina propria is folded the muscularis mucosa is about the same as
in any other organ the submucosa is about the same but muscularis externa is
also modified rather heavily in the stomach so if we look at the muscularis
externa you can see in the cartoon on the Left we have a longitudinal layer
right that’s the outermost layer got it check we got a circular layer we’re also
used to seeing that but what we’re not used to seeing is this innermost oblique
layer so there’s a third layer of smooth muscle in the muscularis externa of the
stomach and while it’s not easy to see I think once I pointed out you’ll be able
to see the distinction in the micrograph on the right you can see right about
here is the borderline between the oblique layer above and the circular
layer below so this is circular and then finally we can see one more transition
and then the longitudinal layer is down here so the the modifications to the
mucosa are largely to facilitate chemical digestion of the ingested food
the acid will denature proteins opening up their site their tertiary and
secondary structures so that the protease enzymes can get in there and
break the proteins up into smaller pieces the modifications to
Galeras are going to facilitate mechanical digestion having that third
layer of smooth muscle running at a 45 degree angle to the other two is going
to allow the stomach to exhibit a characteristic motion called churning
which is going to allow it to really work those digestive enzymes into the
chewed and swallowed food creating an acidic paste called chyme which will
then exit the stomach via the pyloric canal and be further chemically digested
by enzymes in the proximal portion of the small intestine so that’s about it
for now we’ve seen how we modify those layers in the stomach to allow the
stomach to be a stomach and not an esophagus and not a small intestine
that’s it for now study hard we’ll see you later

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