Digestive histology 4- Muscularis externa

Digestive histology 4- Muscularis externa


– All right. Our next layer. I’m going to draw–Pictionary. Let’s do this. Are you ready? My next layer looks a little
something, something like this. Hmm, what kind of tissue are you
going to guess that this is? I know you can do it. That is smooth muscle.
We’ve seen it. I have to draw it in this color. Smooth muscle and this is
actually–okay. This is really cool. This layer
is called muscularis externa. Here we had muscularis mucosae
because it’s part of the mucosa. Here’s we have
muscularis externa because it’s part of the
external portion of my tube. It’s made out of smooth muscle.
Oh, I already wrote that part. Let’s write muscularis externa. That says muscularis externa. What was I going to tell you
about it? Muscularis externa is generally
thicker than muscularis mucosae. And there’s two layers of it.
Now, watch and be amazed. Muscle tissue–muscle cells
are longer than other cells. They tend to be really
elongated cells. And smooth muscle kind of takes
a shape of–I don’t know. I’m going to draw you
a smooth muscle cell. They kind of look like this.
Kind of long and thin. They’ve got their little–as
opposed to like a circular cell or even a cuboidal cell. A smooth muscle cell
kind of has a long– I can’t remember the word they
use to describe that shape. If you imagine that– if like we zoomed in to
look at these cells, we’re going to see them being
kind of long like this. And almost kind of
skinny and flat. But lots of them and they’re
grouped together. And they literally look smooth. We’re not looking at our other
types of muscle tissue. But the sooner
you get comfortable identifying smooth muscle,
the happier you’re going to be because it makes
identifying these different layers
really easy. In the muscularis externa,
because the smooth muscle cells are kind of long can you imagine
that we could put them all in a row? Like we could orient them all
in the same direction. And in fact,
that’s what happens. In multiple layers of
muscularis externa one layers is all oriented in
one direction. And then there’s another layer. And this second layer is
orientated in another direction. And I’m drawing
my other direction with a bunch of circles because
do you agree that if I cut this cell right down
the middle of it and then looked
at the end of it, it would look like a little
circle with possibly a dot in it if I caught the nucleus. So this just indicates that
it’s the same tissue type but one layer of muscularis
externa has the cells oriented in a circular fashion
around the tube. Do you see that? When these shorten,
when they contract they’re going to shorten
along this line and they’re basically going to
decrease the diameter of the tube when they contract. Do you agree with that? Because muscle tissue, its
entire function is based on the fact that it is contractile
tissue, so it does shorten. And when it is oriented in this
kind of long circular way, it’s going to shorten and
decrease the diameter. How are these guys oriented? Okay, I’m making some green
smooth muscle cells. How are they oriented?
Think about this for a second. They’re oriented like this
way in my tube. So when they shorten, they’re
going to shorten this way. And they’re actually going to
shorten the whole tube. Why? Why would you need
to have these layers? One of them going like this and
one of them going like this, so that your tube is actually
shortening and lengthening and decreasing in diameter and
increasing in diameter. Really? Why would we
have that happening? One of the functions of
the digestive system is to move stuff through. You have to move
your food through from the start to the finish. And in order to get your stuff
to move your muscle tissue– your smooth muscle
has to contract. It’s the process of peristalsis. And you can look up peristalsis
on YouTube and entertain yourself a lot
because it’s really fantastic how the tube literally squishes
the food forward. How does it do it? It does it
because of muscularis externa. I think that’s it.
Let’s move on to the next layer.

9 Replies to “Digestive histology 4- Muscularis externa”

  1. I thank that layers of muscularis externa ( circular and longitudinal ) should be reversed. The inner layer of muscularis externa is circular ,outer layer of m.e is longitudinal .?

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