Epithelial tissues are classified based on two main criteria: the shape of the cells and the number of cell layers present. Cell shapes include:
- Squamous: flattened and thin cells
- Cuboidal: cube-shaped cells (about as wide as they are tall)
- Columnar: rectangular cells (taller than they are wide)
Cell layering includes:
- Simple epithelium: a single layer of cells
- Stratified epithelium: multiple layers of cells, with only the bottom layer resting on the basal membrane
- Pseudostratified epithelium: a single layer of irregularly shaped cells giving the appearance of multiple layers
- Transitional epithelium: a specialized form of stratified epithelium where cell shape and number of layers can vary depending on tissue stretch
Thus, the classifications combine shape and layering, for example:
- Simple squamous
- Stratified cuboidal
- Pseudostratified columnar, etc.
This classification helps describe the structure and function of the epithelial tissue in different body locations.
