 Let's just look at these in general. We'll start with epithelial tissues. Epithelial tissues have the job of lining and covering body surfaces. Anywhere you have a surface on your body, you're going to find epithelial tissue. So if we think about the skin, that's epithelial tissue. If you stick your finger in your mouth and touch the inside of your mouth, you're touching epithelial tissue. If we could shrink down into the size of a water molecule and go into one of our sweat glands, we would find that sweat gland is lined with epithelial tissue. All ducts that are lined with epithelial tissue, glands are lined with epithelial tissue. If you stuck your finger in your ear as far as you go, you're going to be touching epithelial tissue. So epithelial tissues line and cover body surfaces. And since that's the case, they always have what we call a free surface. And that free surface is just what it sounds like. It's the part of the tissue that's not touching another tissue. In other words, it's covering or lining that particular surface. Another thing about epithelial tissues is they always have a basement membrane. They always have a basement membrane. That basement membrane is on the other side of the free surface. And it's what attaches the epithelial tissue to whatever tissues are deep to that. So one side is the free surface of the tissue, and the other side is what we call where the basement membrane is found. Now, epithelial tissues can be either simple or they can be stratified. Simple epithelial tissues have only one layer of sales. So in a few minutes, we'll talk about simple squamous epithelium, for example. And simple squamous epithelium has one layer of sales. A stratified tissue, on the other hand, has more than one layer of sales. We'll say layers of sales. So epithelial tissues may be simple or they may be stratified. Let's think about some functions of epithelial tissues, just some general kinds of things that epithelial tissues do. One thing epithelial tissues may do is they may be involved with protection. It makes sense that if they line and cover the body surfaces that we have to have some sort of protection there. And so that's often what we call the first barrier of defense. If an organism gets inside of your body, it has to do so by crossing some membrane, and that's where epithelial tissue comes in. Epithelial tissues are also useful for secretion. We'll look at some goblet cells in a little bit, and the goblet cells secrete mucus. And so any time we have secretion going on, then there may be an epithelial tissue involved. Epithelial tissue can also be involved with moving cells or debris, and we'll look at some examples of that. But the lining of the fallopian tubes or the uterine tubes, for example, contains a ciliated epithelial tissue that helps to move the egg cell gently down towards the uterus. So protection, secretion, moving cells, and debris are all examples of what epithelial tissue is involved with.