Stratified Epithelium - Histology

What is Stratified Epithelium?

Stratified epithelium is a type of epithelial tissue characterized by multiple layers of cells. Unlike simple epithelium, which has only one layer, stratified epithelium has two or more layers, providing greater protection against physical and chemical wear and tear.

Classification of Stratified Epithelium

Stratified epithelium can be classified based on the shape of the cells in the outermost layer:

Stratified Squamous Epithelium: The outermost cells are flat and scale-like.
Stratified Cuboidal Epithelium: The outermost cells are cube-shaped.
Stratified Columnar Epithelium: The outermost cells are column-shaped.

Where is Stratified Epithelium Found?

Stratified epithelium is commonly found in areas subjected to high levels of abrasion and friction. For example:

Epidermis: The outer layer of skin, primarily composed of stratified squamous epithelium.
Oral Cavity: The lining of the mouth, which also consists of stratified squamous epithelium.
Ducts of sweat glands: Often lined with stratified cuboidal epithelium.
Male Urethra: Contains areas of stratified columnar epithelium.

Functions of Stratified Epithelium

The primary function of stratified epithelium is protection. The multiple cell layers act as a barrier against:

Physical abrasion
Pathogens
Chemical damage

In addition to protection, stratified epithelium also plays roles in secretion and absorption, particularly in glandular structures.

How is Stratified Epithelium Structured?

The structure of stratified epithelium can vary depending on its type:

In keratinized stratified squamous epithelium, found in the skin, the outermost cells are filled with keratin, a tough, protective protein.
Non-keratinized stratified squamous epithelium, found in moist areas like the oral cavity, lacks keratin but still provides robust protection.

Stratified cuboidal and columnar epithelia are generally less common and are usually found in specific glandular ducts, providing additional protection and sometimes aiding in secretion.

How is Stratified Epithelium Identified in Histological Stains?

Stratified epithelium can be identified in histological stains by observing multiple cell layers with varying shapes. Common stains include hematoxylin and eosin (H&E), which stains the cell nuclei blue (hematoxylin) and the cytoplasm and extracellular matrix pink (eosin).

Clinical Relevance of Stratified Epithelium

Changes in stratified epithelium can indicate various pathological conditions:

Dysplasia: Abnormal development of epithelial cells, which can be a precursor to cancer.
Carcinoma: A type of cancer arising from epithelial tissue.
Hyperkeratosis: Thickening of the outer layer of the skin, often due to chronic irritation or inflammation.

Histological examination of stratified epithelium is crucial for diagnosing these conditions and planning appropriate treatments.