Digestive histology 9- Small intestine

– Now we’re going to look
at the three parts of the small intestine. Let’s go ahead and jot them
down, what comes first? Duodenum. What comes next? Jejunum. That’s says jejunum.
What comes next? Ileum, with an E like eat. Now, I’m going to tell you that
characteristic things that you’re going to look for
in each of these. They’re all parts
of the small intestine. They’re all going to have villi. They’re all going to
have microvilli. They’re all going to have
all of our layers. All of them are lined with
simple columnar epithelium. All of them have two layers
of muscularis mucosae. To distinguish
between them, here’s what you’re going
to look for. In the duodenum, holy–in fact,
I’m writing that down. Holy glands. Not in the mucosae. Not in the lamina propria
like in the stomach. The stomach was full of glands. These glands are
in the submucosa. If you see a submucosa and it
looks like a bubbly bubble land, then you know you’re
in the duodenum. And I’m going to show you
a picture here in a second. In fact, dude, I better just go
show you a picture right now. How are you going to know if
you’re in the submucosa? You have to find
muscularis mucosae. And so look here,
this is my epithelial tissue. Look simple columnar epithelium
which means that all of this is lamina propria. And we do have some glands in
there. But look. Look at that line.
That is muscularis mucosae. Now zoom out. What? Look at this glandular tissue. You’ve got to be–I mean
holy gland madness. If you see that kind of
glandular tissue in like deep to muscularis
mucosae–there is our line of muscularis mucosae. If you see that you know you’re
in the duodenum. Just look for those glands.
I mean that’s crazy talk. That doesn’t even look
like stomach. That’s even crazier than that.
Holy glands. Right? Perfectly clear. Let’s do the ileum next
because the ileum has one that is really,
really obvious. Lymphatic nodules.
Holy lymphatic nodules. Not modules. Nodules. And those lymphatic nodules are
called Peyer’s patches. Sometimes the Peyer’s patches
are found in the mucosa. Sometimes they’re found
in the submucosa. And so where they’re located
doesn’t tell you anything. The number of them
tells you something. The more Peyer’s patches
there are, the more lymphatic nodules
there are, the more you know that, okay,
I’m probably in the ileum. Lymphatic nodules are
everywhere. They’re all over
the digestive system. In fact, lymphatic nodules are
part of the immune system. They’re part of– it’s almost like a little lymph
node type structure. And your lymphocytes
hang out there. And in fact what is it like 80%
of all your lymphocytes hang out in
your digestive system because they’re making sure
that, dude, who knows what you ate. Especially if you’re
my smallest child. That kid–I mean everything goes
in his mouth. And so you know that there is
going to be something gnarly in there that you want to
protect–do not let this substance into my body. So let’s put a whole bunch of
troops guarding the area. So, yeah, absorb as much as you
want from the lumen of your gut. But let’s have the troops
there to make sure that what you’re absorbing isn’t
going to make you sick. I just saw a lymphatic nodule in
the duodenum. And so I want to show–oh, wait
come back. I want to show it to you so that
you can get a sense of what it looks like. Check it out. This is awesome. Don’t go by color. Never go by color when you’re
studying histology. But look at the shape. These are my duodenal glands all
over in the submucosa. Look at this.
I mean it’s just weird. It’s almost like dense. But regular and it’s not
connective tissue. It’s really dense
cellular tissue. This is a lymphatic nodule. And look at how the tissue
is different. Here’s my glandular tissue. This looks like maybe even
a smooth muscle layer. Possibly dense irregular
connective tissue. Let’s zoom out. Do you see how–I mean that
tissue looks really different, doesn’t it? That’s what your lymphatic
tissue is going to look like. I’m wondering if there’s any
other–do you see another one? Totally. You’ve got
another one in here. Now, here’s another one
right there. I mean you don’t even have to
zoom in to confirm. Let’s do. We’ll totally zoom in here and
make sure that it looks like that same like kind of dense
polka dotty– how do you describe that? I describe it
like lymphatic tissue. Do you want to see how many
lymphatic nodules are found in the ileum? Zooming way out you can still
see these things. There’s one. There’s one. These guys are actually all
in the submucosa. There’s one. Cool. Along with
all those duodenal glands. There’s like three
or four of them. Ready? You’re not going to
believe this. What? There is one.
Now I can’t zoom in here. This is an ileum. I’m not fond of the ileum
example that they have in the Michigan slide. So I went out into the world. Oh, and it looks like I can’t
see. I’m not cool with that. But check it out.
Look at how many there are. 1, 2, 3, 4. Don’t they look like
big blobular structures? And if we could zoom in we’d
see that they’re made up of that really dense stuff. These look like they’re actually
in the submucosa. Sometimes Peyer’s patches extend
into the mucosae– I mean the lamina propria. And so you can’t really tell
based just on that. But look here we have villi. We have normal structures
that we can find all the way out around
in the other parts of the small intestine. But if I’m going to ask you to
identify the ileum, I’m going to make sure that
there are billions of Peyer’s patches for you
to see and that it’s really obvious. Sometimes the Peyer’s patches
are just on one side of the tube. But again it’s really obvious. So the last one, I’m thinking
that the last one is almost the process
of elimination. There are a couple of
characteristics that are really distinctive about
the jejunum. They have
really long thin villi. All of them have villi. For whatever reason the
jejunum–and we can actually try and speculate on why
that is the case. The jejunum has really, really
lots and lots of long thin ones. And something that happens–now
imagine. You have a tube. And in your tube it’s lined with
all these crazy long, spaghetti-like tentacles,
the villi. And then I take a section
and my villi kind of move over a little bit
and they smear. And I end up taking a section of
villi like that. Do you agree that if I had that
I would actually– what I would see is a whole
bunch of kind of circle shapes? Can’t remember if I have a
jejunum for you to look at. It almost looks like zebra–
I mean not zebra, but giraffe skin. Like the shape of a giraffe. Okay, I’ve got to go see
if I have any jejunum. I don’t think I got jejunum.
Why didn’t I? That makes me kind of want to go
see if I can find some jejunum. This is a giant–like what are
the chances that it looks how I want to show you what
it looks like? Okay, this kind of works. Does it work–look that’s that–
that giraffey looking shape that I was imagining. But it was–it’s more like
in this space. See how like we take–
you can imagine. That doesn’t look like
long thin villi to me. But it’s because we cut
a slice and they were all in a tangle when we cut the slice. So we got all kinds of different
angles on our tangles. When you look at jejunums you
will be like oh, yeah, okay. You will get a sense for this
kind of– something that looks like this
actually means that we have long thin villi. The jejunum is kind of a process
of elimination. I think jejunum and stomach are
equally challenging. And I think easy to confuse. But if you look for those
long thin crazies that’s what you’re aiming for. That was our small intestine.
Let’s do our large intestine.

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