01.02 Types of Epithelial (Skin) Tissue

In this lesson we're going to talk about the different types of epithelial tissue and where they’re found.

If you remember from the epithelial tissue video, we classify epithelium based on how many layers there are and the shape of the cells at the top of those layers. Simple means that has one layer and stratified means it has multiple layers. So let's look at these different types of epithelium a little bit closer.

First is simple squamous. It is a single layer of flat cells. The primary functions of simple squamous epithelium are filtration, like in capillaries - diffusion, which happens through the membranes that line body cavities - and gas exchange, which happens in the alveoli.

Next is simple cuboidal - this is a single layer of cube-like cells. We find this type of epithelium in coverings like around the lens of the eye or linings of kidney tubules, as well as in the ducts of exocrine glands. Make sure you check out the glands lesson to see more of this.

Then there’s simple columnar, this is a single layer of column-like cells. Some of these are mucus secreting like in the stomach or goblet cells. Others have cilia, which are tiny hair-like structures that help to move substances past the cells - this happens in the respiratory and reproductive tracts. And others have microvilli, which are finger-like projections that help increase absorption, like in the small intestine and GI tract.

The next type of epithelial tissue is kind of a specialized type - it’s called pseudostratified ciliated columnar. Let’s break these words down - we just talked about ciliated, right? So we know it has the little hair-like projections. We also know stratified means many layers, right? But the ‘pseudo’ part means it’s not really stratified - it’s fake stratified. So why is that. Well, what happens is you have your basement membrane and all the cells are sitting on it - so it’s only one layer of cells. But some of those cells are shorter or smaller than others and don’t make it all the way out to that free surface. So when you look at it in a microscope, the nuclei are at all different heights, which makes it seem like there are multiple layers - hence why we call it pseudostratified. You even have some goblet cells in here to secrete mucus, and remember it has cilia. So where would we find cells that have mucus and cilia? The respiratory tract! It’s how we are able to get the junk and bacteria out of our lungs.

The next type is actually stratified - it’s stratified squamous. Remember the squamous part refers to the TOP layer of cells, so you may have any shape down below, but the very top layer is going to be flat. This type of epithelium can be keratinized, meaning it contains keratin for water-proofing - that would be found in the epidermis of the skin. The keratin keeps us from soaking up water like a sponge. Or we can have non-keratinized stratified squamous epithelium, which is found in our mucous membranes like the inside of the mouth and throat, and the vaginal canal.

We can also have stratified cuboidal where there are multiple layers, but the top layer is cube-like. This is found in the ducts of sweat glands… and that’s about it. It’s not very widespread in the body.

Next is stratified columnar - I know you’re getting this by now. Multiple layers of cells with column-like cells in the top layer. These can either be ciliated, like in the larynx, or non-ciliated, like in the urethra, depending on the purpose. As you can see, this type isn’t very widespread either.

The last type is called Transitional or Uroepithelium. It is stratified, meaning it has multiple layers. But the top layer varies - or transitions (hence the name) from flat to globular shaped. This type of epithelium is only found in the urinary tract, hence the name “uroepithelium”.

So let’s quickly recap what you need to know about each type of epithelial tissue. Make sure you can picture and understand the shape of the cells and layers based on how we classify it. You also want to know the main locations. It might be a body system or some sort of specialty function like a mucous membrane. Then make sure you know the specialized functions. Cilia move substances past the cells, microvilli help with absorption, goblet cells secrete mucus, and keratin helps to waterproof the tissue - specifically the skin.

That’s it for types of epithelial tissue. Make sure you check out the resources and images attached to this lesson! Now, go out and be your best selves today. And, as always, happy nursing!