We can have simple epithelium, we can have stratified epithelium and we can also have something known as pseudostratified epithelium and we'll see what that means in just a moment. First, let's discuss simple and stratified epithelium. Now, a simple epithelium means that we have a single layer of cells across the entire basement membrane and we'll see what the basement membrane is in just a moment. And simple epithelium is usually found in that region of our digestive system that requires secretion and or absorption. On the other hand, stratified epithelium simply means we have many layers of our epithelial cells stacked on top of one another and this type of epithelium is usually found in those regions that is exposed to a continual amount of mechanical and chemical stress. And we'll see what that means in the next several lectures.