TYPES OF COVERING EPITHELIA
There are several types of covering or lining epithelia. They are classified mainly according to two criteria:
- amount of their cell layers.
- shape of their cells.
If an epithelium consists of only one layer of cells, it is classified as a simple epithelium. If it consists of two or more layers, it is called a stratified epithelium.
Some types of epithelium do not fit neatly into these two categories and require additional criteria for their classification. These will be explained on the following pages.
The cell shape criterion is applied differently depending on whether the epithelium is simple or stratified:
In a simple epithelium, the classification is based on the shape of the cells in the single cell layer.
In a stratified epithelium, the classification is based on the shape of the cells in the outermost layer, that is, the layer farthest from the underlying connective tissue.
This may sound complicated at first, but the principle is quite simple. Beginning on the next page, we will examine the different types of covering or lining epithelia and learn how to recognize and classify them.