[Music] Recently, I discovered on Wikipedia that David Beckham, Angelina Jolie, and I are all the same age. That got me thinking. Do we have anything else in common? Are we all fabulously wealthy, incredibly [Music] good-looking, maybe famous all around the [Music] world? Well, I may not be any of those things, but we do share at least one other thing in common. Each of us has two parts to our name. a first name and a last name. And guess what? So does epithelial [Music] tissue. In epithelial tissue, the first name always indicates the number of cell layers whilst the second name indicates the shape of the cells. [Music] Let's look at the number of cell layers first. If only one layer of cells is present, we call the epithelium simple. Simple epithelium is found where rapid absorption or diffusion occurs because material can pass really quickly through just one layer of cells. If more than one layer of cells is present, we call the epithelium stratified. Stratified epithelium is located in regions where we need protection against abrasion, friction or bacteria like for example the skin. Next, let's look at the shape of epithelial cells. If the cells are flat, we call the epithelium squamus. If the cells are cube like the epithelium is cubuidal and if the cells are column shaped, the epithelium is columnar. So to summarize, if you're asked to name epithelium, first state the number of cell layers present and then the shape of the cells. Here are some common examples of epithelium. Simple squamus, simple cubuidal, and simple columna. Then there's stratified squamus, stratified cubuidal, and stratified columnar. But wait, there's more. Our bodies have two other very special types of epithelium which I haven't yet mentioned. These are pseudo stratified columnar epithelium and transitional epithelium. This is what pseudoratified columna epithelium looks like. Pseudo means false. The epithelium looks stratified but it's actually not. There is only one layer of cells present because all of the cells touch the basement membrane. Pseudoratified columnar epithelium secretes a sticky mucus and has psyia on its surface. It's found in the nasal cavity and trachea. The mucus traps dust in the air preventing it from getting to your lungs and psyia move the dust and mucus towards your throat where it's swallowed. Finally, let's look at transitional epithelium. Transitional epithelium is a special type of stratified epithelium that can stretch without breaking. Transitional epithelium is found in the bladder because the bladder has to stretch as it fills with urine. In an empty bladder, the cells are cuboidal in shape. But as the bladder fills with urine, the epithelial cells stretch and become squamus in shape. It's because the cells change shape that we call this epithelium [Music] transitional. Thanks for watching. Subscribe to my YouTube channel and stay tuned for more Human Biology Explained videos. [Music]