In this video, we're going to begin our introduction to epithelial tissue. And so, recall from our previous lesson videos that epithelial tissue is one of just four primary types of tissue found in the human body. And epithelial tissue is commonly abbreviated as just epithelia without the L and without the tissue. And so, epithelia or epithelial tissue is tissue that covers body surfaces and many organs, lines, internal body cavities and ducts and makes up glands or cellular structures that are specialized for secretion or releasing products. And so covering lining and glands are key terms that are very often associated with epithelial tissue in your textbooks. However, one of the key defining features of most epithelial tissue is that it consists of a single sheet or multiple sheets of tightly packed cells on a boundary immediately adjacent to open space. In fact, if we take a look at our illustration down below, you'll notice that we're highlighting a few examples of where epithelial tissue can be found in the human body. And what you'll notice is that in each of the micro graphs, for these examples, we can clearly see that epithelial tissue is going to consist of sheets of tightly packed cells on a boundary adjacent to open space. In fact, we can actually highlight the open space in each of these micro graphs. And so notice on the far left over here, you can see the open space is right here in this region. In the second micrograph, you can see that there's open space right over here. In this third micrograph, you can see that there's small bits of open space in these highlighted small regions that you see there. And then in this final micrograph, once again, you can see that there's small bits of open space in these highlighted regions right there. And so over here in the micrograph, on the far left, notice that it is indicating that the outermost layers of our skin is going to be epithelial tissue. And we know that our skin covers our entire body surface. And so the outermost layers of the skin is a classic example of epithelial tissue. Now, we also know that epithelial tissue is going to be important for lining internal body cavities, including lining of our airways. And so notice that this second example is showing that the lining of our airways is going to contain epithelial tissue. And we also know that epithelial tissue is important for forming or making glands. And so that's going to include salivary glands and salivary glands are going to be found in our mouth and they are going to secrete or produce saliva And then last but not least we know that epithelial tissue is important for uh lining ducts and forming tubules as well. And so notice in this last example, we're showing you that the ducts and tubules found in our kidney are going to contain epithelial tissue. And so once again, this is just our brief introduction to epithelial tissue. And as we move forward in our course, we're going to continue to learn a lot more about epithelial tissue. And so this concludes this introduction and I'll see you in the next video where we'll talk more about the functions of epithelial tissue.