In this video, we're going to talk about the first type of simple epithelial tissue in our lesson, which is simple squamous epithelium. And so before we get started, I want to draw your attention to the numbering and lettering system that we're using for these tissues. Here, it's one egg. And so what I really want you to notice is that we're using the number 1 for all of the simple epithelial tissue. And so recall the term simple indicates the tissue has just one single layer of cells where all of the cells come into contact with the basement membrane.
And so we can use the number 1 in our numbering system as a memory tool to remind us that once again, all of the simple epithelial tissues have just one single cell layer where all of the cells are going to come into contact with the basement membrane. And so the letter 'a' here is indicating that this is the first type of simple epithelial tissue that we're covering in our lesson. Here, it's simple squamous epithelium. And so moving forward, when we cover the other 3 types of simple epithelial tissues, you'll notice that they're going to be numbered and lettered as 1b, 1c, and 1d, where, again, the one is indicating this is a simple epithelial tissue with just one layer of cells. And then after we cover all 4 of the simple epithelial tissues, we'll then transition to talking about the 4 stratified epithelial tissue.
And those will be numbered and lettered as 2a, 2b, 2c, and 2d. Where again, the number 2 is indicating that these stratified tissues are made of 2 or more layers of cells. But again, we'll cover these stratified epithelial tissues later in our course in different videos. And for now, we're focused on simple epithelial tissues, more specifically, simple squamous epithelium. So notice that on the left, we have some text that's showing you some of the most important characteristics, functions, and body locations of where this tissue can be found.
And we also include a helpful ID tip just in case you need to identify this tissue under the microscope. And so with each tissue, we're going to include an image to help support your understanding. And so once again, when it comes to simple squamous epithelial tissue, we know that the term simple implies that the tissue has just one single layer of cells. And so recall that the term squamous implies that the shape of the cells is going to appear squished or flat. And so simple squamous epithelium is going to consist of just one single layer of squished or flat cells.
Just like what you can see over here in our diagram. Notice that we have just one single layer of cells where all of the cells are in direct contact with the underlying basement membrane that we briefly talked about in our previous lesson videos, and you can see as indicated here in our diagram. And really, that's the defining feature that makes it one layer of cells is when all of the cells come into contact with that basement membrane. And notice that we have these flattened cells here. Again, the term squamous is Latin for scales, which are flat as well.
And so these cells are so flat or squished that they're actually going to have less cytoplasm than other tissues that have cells with different and bigger shapes. And also, these cells are so flat that they actually create a pretty flat surface that makes it really easy and smooth for liquids to be able to flow on top of this tissue. And so we tend to find simple squamous epithelial tissue in areas of the body where liquids need to be able to flow smoothly. Like for example, simple squamous epithelial tissue is found lining all of the hollow organs of the cardiovascular system, such as the capillaries and the larger blood vessels and the heart as well. Now what you'll notice is that the nuclei of these cells is pretty centrally located, And this is really what makes the simple squamous epithelial cells look like fried eggs.
And so you can think that the flat nature of the fried egg is just like the flat nature of the simple squamous cell. And notice that the yolk of the egg, which is pretty centrally located, can represent the centrally located nucleus of the simple squamous cells. And so, hopefully, thinking of fried eggs can remind you of the structure of the cells within simple squamous epithelial tissue. Now, when it comes to the functions, it's actually the structure of the tissue in the cells that's going to dictate the function. And so once again, simple squamous epithelial tissue consists of a single layer of these flat cells, and that's going to make the thinnest possible epithelial tissue.
And because it's so thin, it's not going to serve a primary protection role. Because when you think about protection, it's going to be the thicker tissues that have multiple layers of cells that are going to be better suited for protection. And so protection will be a bigger function in stratified tissue. But again, with simple squamous epithelial tissue, protection is not going to be the primary role for this tissue. And so, again, the function is going to be dictated by the structure.
And once again, simple squamous epithelial tissue is going to be the thinnest epithelial tissue. And because it's so thin, it's actually going to allow for the rapid diffusion of molecules across this thin tissue. And so, it's going to allow for the quick exchange of substances across the tissue. And so again, one of the primary functions here is going to be rapid diffusion. And so we can actually expect to find simple squamous epithelial tissue in body locations that require rapid diffusion.
For example, we can find simple squamous epithelial tissue lining the air sacs of th