What is Stratified Epithelium?
In histology,
stratified epithelium refers to a type of epithelial tissue characterized by multiple layers of cells. The term "stratified" comes from the Latin word "stratum," meaning layer, which aptly describes the arrangement of cells in these tissues.
Types of Stratified Epithelium
Stratified epithelia are further classified based on the shape of the cells in the outermost layer. Some common types include: Stratified Squamous Epithelium: This type has flat cells in the outermost layer and is found in areas subject to abrasion, such as the skin and the lining of the mouth.
Stratified Cuboidal Epithelium: Comprising cube-shaped cells, this type is typically found in the ducts of sweat glands and salivary glands.
Stratified Columnar Epithelium: This type has column-shaped cells in the outer layer and is rare, usually found in parts of the pharynx and the male urethra.
Transitional Epithelium: Also known as urothelium, this type can stretch and is found in the urinary bladder and other parts of the urinary tract.
Functions of Stratified Epithelium
The primary function of stratified epithelium is
protection. Due to its multiple layers, it provides a robust barrier against mechanical stress, dehydration, and microbial invasion. For example, stratified squamous epithelium in the skin protects underlying tissues from physical damage and pathogens.
Skin: The epidermis is made of stratified squamous epithelium, which is vital for protection.
Oral Cavity: The lining of the mouth is another example where stratified squamous epithelium provides protection.
Esophagus: The esophageal lining is also made of stratified squamous epithelium to withstand the passage of food.
Urinary Bladder: Transitional epithelium lines the bladder, allowing it to stretch and contract.
How is Stratified Epithelium Formed?
Stratified epithelium is formed through the differentiation and proliferation of
basal cells located in the deepest layer of the epithelium. These basal cells divide and push older cells towards the surface, where they eventually flatten and die, especially in keratinized tissues like the skin.
Histological Staining of Stratified Epithelium
Histological staining techniques, such as
Hematoxylin and Eosin (H&E) staining, are commonly used to visualize stratified epithelium under the microscope. Hematoxylin stains the cell nuclei blue, while eosin stains the cytoplasm and extracellular matrix pink, providing a clear contrast to observe the multiple layers of cells.
Clinical Relevance
Alterations in stratified epithelium can indicate various pathological conditions. For instance, dysplasia and hyperplasia in stratified epithelia can be precursors to cancer. Conditions like
Squamous Cell Carcinoma arise from the stratified squamous epithelium, highlighting the importance of regular histological examinations for early detection.
Conclusion
Stratified epithelium plays a crucial role in protecting the body from various forms of damage. Its ability to form multiple layers of cells makes it ideally suited for areas subjected to mechanical stress and environmental exposure. Understanding its structure, function, and clinical significance is essential for both histologists and medical professionals.
