Stratified squamous epithelium is a tissue type forming protective linings throughout the body. It is characterized by multiple layers of cells, which is what “stratified” refers to. The outermost cells are flattened, a shape described as “squamous.” This multi-layered structure provides robust protection against physical abrasion, friction, and environmental stresses. Its primary function is to act as a barrier, safeguarding underlying tissues from damage and preventing microorganism entry.
Keratinized Stratified Squamous Epithelium
Keratinized stratified squamous epithelium is found primarily in the epidermis, the outermost layer of the skin. This specialized tissue contains keratin, a tough, fibrous protein. Keratinocytes, the cells that produce keratin, mature and flatten as they move from the deeper layers to the surface of the skin, eventually dying and forming a durable, water-resistant layer.
This keratinized layer, known as the stratum corneum, makes the skin highly resistant to mechanical stress and acts as a significant barrier against water loss, preventing desiccation. It also provides protection against chemical damage and microbial invasion. The continuous production and shedding of these keratin-filled cells ensure constant renewal, maintaining the skin’s protective integrity.
Non-Keratinized Stratified Squamous Epithelium: Oral Cavity and Esophagus
In contrast, non-keratinized stratified squamous epithelium lacks the thick, tough keratin layer, making it softer and typically moist. This type of tissue lines various internal surfaces that experience mechanical stress but also require flexibility and a moist environment. The oral cavity, including the mouth, pharynx, and parts of the tongue, is extensively lined with non-keratinized stratified squamous epithelium. This lining withstands the constant abrasion from chewing and swallowing food, while remaining pliable for speech and taste sensation.
The esophagus, the muscular tube connecting the throat to the stomach, also features this type of tissue. Its non-keratinized lining provides protection against the abrasive effects of food as it passes through to the stomach. The moist surface facilitates the smooth passage of food, ensuring lubrication without the need for the dry, hardened protection of keratin.
Non-Keratinized Stratified Squamous Epithelium: Other Internal Linings
Non-keratinized stratified squamous epithelium is also found in other internal body linings that require both protection and a moist, flexible surface. The anal canal, for instance, is partly lined with this tissue, particularly in regions that transition from the rectum to the external skin. Here, it protects against friction and abrasion during the passage of fecal matter, with its moist surface aiding in lubrication.
The vagina also contains non-keratinized stratified squamous epithelium, providing a protective barrier against friction and potential microbial entry. The constant shedding of cells in the vaginal lining contributes to its defense mechanisms. The true vocal cords, which endure constant vibration and airflow during speech, are covered by this specialized non-keratinized epithelium. Its flexibility is essential for sound production, offering protection from mechanical strain without impeding vibration.