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- Understanding Epithelium: Review, Practice Questions, and Identification Techniques
Understanding Epithelium: Review, Practice Questions, and Identification Techniques
Learn how to identify epithelium by understanding the number of layers and shapes of cells. Review and practice questions included for better comprehension. Squamous, cuboidal, and columnar cell shapes explained with tips on recognizing cuboidal cells with rectangular appearance.
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Video Transcript
So what I'm going to do is show you one example of each
and then ask a series of questions
to see if you can identify the epithelium I just showed you
using the techniques I just explained.
So when you're identifying epithelium,
you really need to ask yourself two questions.
First, how many layers of cells am I seeing?
And what are the shape of those cells that I'm seeing?
So when you're seeing one layer of cells that is a simple epithelium, multiple layers of cells would
be a stratified epithelium. And our three possible shapes are squamous, which are flat, cuboidal,
which are squares, and columnar, which are columns. The only slight trouble
occurs
when sometimes cuboidal cells, they might look a little bit rectangular. So in that
case, look at the nuclei. If the nuclei is a nice little circle, it's going to be
cuboidal. If it is an oval, it is going to be columnar. So on our first example, we
are seeing a singular layer of square-shaped cells, and that's why this
is simple cuboidal. So you're seeing that in a couple examples on this slide. If
you were unable to tell what shape these cells were, look at the circular nuclei.
Remember simple cuboidal has circular nuclei. In our next example,
You're seeing the basement membrane. Remember epithelium always has to be
attached to something and that something is the basement membrane. And you have a
single row of cells going off this way and a separate singular layer of cells
going off this way. And you can see little rectangular outlines which is how
you know this is, simple columnar. Now if you couldn't see the outlines, you can
also look for those oval shaped nuclei. You can also look sometimes, but not
always, you'll have these specialized little cup shaped cells called goblet
cells. In the next slide, what you're seeing is the same type of epithelium at
two different magnifications. So when you're looking at it at a high high magnification,
you can see one layer
flat cells. So this is simple squamous. In this example, your first instinct is to
probably think that you're seeing multiple layers of cells because you're
seeing multiple layers of nuclei. But what you're actually seeing is you have
little short cell here and then you have some tall cells but they're all attached
to the basement membrane so this is really only one layer. So this is the
ciliated pseudostratified columnar epithelium. It is called ciliated
because it has cilia on top. Pseudo-stratified. Pseudo means fake like pseudoscience.
is fake science. Pseudostratified means fake layers and the taller cells would
be column shaped. In this example, so this is the basement membrane down here,
you're seeing many cells, so it is stratified. And if you pay attention to
the shape of the cells at the top, you can see they're very flat little
pancakes. So this is stratified squamous. Even though the cells towards the bottom
are more cube-shaped, we only care about the cells on the top when we're picking
the name. And this last example does not follow the naming pattern. So it is
stratified because there are more...
little layers of cells stacked on top of each other, but they're not really
squamous, they're not columnar, they're not cuboidal, so this just gets its own
name. This is transitional epithelium. So if you're looking at an epithelium
that's stratified and you feel confused about the shape, it's probably
transitional. Your other hint is if you look at the top, usually the cells at the
look like little bubbles. So now I want you to think for yourself, what am I
