What Is Epithelial Tissue? - Function, Types & Structure

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  • 1:05 Columnar, Cuboidal,…
  • 1:42 Simple and Stratified…
  • 2:36 Psuedostratified…
  • 3:58 Transitional Epithelium
  • 5:04 The Basement Membrane
  • 5:37 The Function of…
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will cover the different shapes and structures of epithelial tissue, including simple, columnar, cuboidal, stratified, transitional, squamous, and pseudostratified columnar epithelium.

Epithelial Tissue

For those of you who grew up playing with Legos, you surely would have noticed that, despite the wide variety of shapes and colors, they were still basically little plastic bricks.

Epithelial tissue, the type of tissue that lines the surfaces and cavities of your body's organs, is no different. Epithelial tissue is like the brand name Lego: Lego has differently sized and shaped blocks, and epithelial tissue has differently sized and shaped cells. Lego blocks can be arranged into differently shaped structures, and epithelial cells can be arranged into differently shaped structures as well.

Regardless of the shape, size, or arrangement of the cells, they are still a type of, or part of, epithelial tissue, just like all our differently sized, shaped, and arranged plastic bricks are still Legos.

Columnar, Cuboidal, Squamous Cell Shapes

Epithelial tissue can have columnar, cuboidal, or squamous cell shapes.
Types of epithelial tissue

Epithelial tissue has differently shaped bricks - or cells, that is. There are columnar cells, which means 'column-like cells'; cuboidal cells, which are cube-like cells; and squamous cells, which are flattened and scale-like cells. Basically, columnar cells are much higher than they are wide, cuboidal cells look like squares, and squamous cells are flat like turtles and therefore not very tall at all.

Simple and Stratified Cell Arrangements

What we've just done in terms of the columnar, cuboidal, and squamous cells is gone over the three different Lego shapes of our epithelium. We can take each of these Lego shapes and arrange them in different ways to build a structure.

If we arrange any cell shape in a single layer, we would call it simple epithelial tissue. Again, simple epithelial tissue is a single cell layer of epithelial tissue. However, if we begin to stack our shapes one on top of another, regardless of whether it's two layers or more, this would be called stratified epithelial tissue, which is an epithelial tissue that is more than one cell layer thick.

Pseudostratified Columnar Epithelium

Unfortunately, life isn't always as easy as we want it to be. There are exceptions to the three shapes and the two different arrangements of layering we just went over.

Pseudostratified means one layer of cells is bent and twisted to make it appear stratified.
Non-stratified epithelium

One of these exceptions is known as pseudostratified columnar epithelium, which is a type of tissue that has a single layer of cells arranged in a fashion that appears stratified. Basically, it's like taking a bunch of very flexible Lego pieces, arranging them in a one-layer-thick structure, but then bending and twisting this one layer to make it look like there is actually more than one layer when that's actually false.

So, it shouldn't surprise you that the prefix 'pseudo' means 'false' in Latin. Hence, something that is 'pseudo' (in our case, pseudo-stratified) looks to be stratified when it's actually not. Since the only alternative to stratified epithelial tissue is simple epithelial tissue, you know that the pseudostratified columnar epithelium has got to be only one layer of columnar cells.

Transitional Epithelium

The second exception to our cell shapes and arrangements is actually pretty darn cool! It's called transitional epithelial tissue. This tissue is transitional, meaning it doesn't stay the same shape for long, as it transitions from one shape to another as necessary. In simple terms, transitional epithelial tissue is an elastic-like epithelial tissue that swells, contracts, and changes shape as necessary in order to accommodate something.

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