Stratified Epithelial Tissues
Stratified epithelium consists of multiple layers of cells. The most superficial cell layer is exposed on the apical side and the deepest cell layer is anchored to a basement membrane on the basal side. These tissues are named for the shape of the cell at the apical side. This chapter will focus on stratified squamous epithelium, which forms our major protective barriers.
Stratified squamous epithelium is part of two important protective membranes, where it exists in different forms:
- Non-keratinized – found in the mouth/esophagus, vagina, rectum/anus
- Keratinized – found in the epidermis of our skin
Keratin is a fibrous protein that provides strength and durability to our hair, skin, and nails. We will discuss this further in the Integumentary System chapter.
Remember back to our introduction to epithelial tissues – we said they were avascular and anchored to connective tissue on their basal side. All nutrient supply for the epithelial tissue is provided by small blood vessels in the connective tissue layer that anchors the epithelium. All nutrients, O2/CO2, water, etc. must travel through the layers of epithelial cells by simple diffusion to provide enough resources to keep each cell healthy. In the keratinized epithelium of our skin, the number of cell layers is just too many, and the cells at the apical side are too far away from the blood supply to receive enough resources to survive. Our body uses this to its advantage! Instead of simply dying, the cells on the apical side become filled with keratin, which provides our skin extra strength and durability.
Non-KEratinized stratified squamous epithelium
Table 1: Non-keratinized stratified squamous epithelium
| Tissue Type | Non-Keratinized Stratified Squamous Epithelium |
|---|---|
| Structure | Multiple layers of cell , apical cells are flattened disc-shaped cells with flattened nuclei; cells of the basal surface may be cuboidal |
| Location | Lining of esophagus, vagina, rectum, and anus |
| Function | Protection against abrasion |
| Presence of keratin? | No |
| Apical surface dry or wet? | Wet – part of the mucous membranes |
Figure 1: Non-keratinized stratified squamous epithelium (esophagus) with and without illustration overlay
Check out our YouTube videos to help you understand non-keratinized stratified squamous epithelium:
YouTube Video – non-keratinized stratified squamous epithelium
keratinized stratified squamous epithelium
Table 2: Keratinized stratified squamous epithelium
| Tissue Type | Keratinized Stratified Squamous Epithelium |
|---|---|
| Structure | Multiple layers of cell; apical cells are flattened, do not have nuclei, and often appear as though peeling away from other layers; cells on the basal surface may appear cuboidal |
| Location | Epidermis of the skin |
| Function | Protection against abrasion and prevention of water loss |
| Presence of keratin? | Yes, soft keratin found in the apical cells |
| Apical surface dry or wet? | Dry – part of the cutaneous membrane |
Figure 2: Keratinized stratified squamous epithelium (thin skin) with and without illustration overlay
IMPORTANT NOTE: Stratified cuboidal and stratified columnar epithelium exist in few locations in the body. Because they are not considered common tissue types, we will not discuss them in this text.
Chapter Illustrations By:
Juan Manuel Ramiro-Diaz, Ph.D.
closer to the surface
the exposed side of epithelial tissue
closer to the center, away from the surface
the anchored side of epithelial tissue
without blood vessels
