stratified squamous epithelium
Summary
Stratified squamous epithelium consists of multiple layers of flattened cells, providing protection against abrasion and mechanical stress. It is found in areas requiring durability, either keratinized (skin/epidermis) or non-keratinized (esophagus, mouth, vagina, anus, cornea). The basal layer is the site of mitotic activity and regeneration.
Detail
Stratified squamous epithelium is composed of multiple layers of cells, with the basal (deepest) layer containing cuboidal to columnar cells that undergo mitosis, and superficial layers becoming progressively flattened (squamous) as cells migrate upward and mature. There are two main types:
1. Keratinized stratified squamous epithelium - found in the epidermis of skin. Cells accumulate keratin and lose their nuclei in the outermost layer (stratum corneum), forming a tough, waterproof barrier resistant to abrasion and desiccation. Layers include stratum basale, spinosum, granulosum, lucidum (thick skin only), and corneum.
2. Non-keratinized stratified squamous epithelium - found in wet surfaces subject to friction, including the esophagus, oral cavity, oropharynx, vagina, anal canal, and cornea. Superficial cells remain nucleated and moist.
Clinical significance: This epithelium type is important in pathology because malignant transformation gives rise to squamous cell carcinoma (SCC), a common cancer arising from stratified squamous epithelium (skin, esophagus, cervix, oral cavity, lung - via squamous metaplasia). Barrett's esophagus is a classic example of metaplasia FROM stratified squamous (esophageal) TO simple columnar epithelium (intestinal-type) due to chronic GERD, increasing risk of adenocarcinoma. Squamous metaplasia can also occur in the trachea/bronchi of smokers (normally pseudostratified ciliated columnar) as an adaptive but pre-malignant response to chronic irritation. Understanding the specific location and type of epithelium is a common way to test embryology, histology, and pathology on Step 1, particularly for identifying tissue origin of biopsies and cancers.
Sources
- Junqueira's Basic Histology
- Robbins Basic Pathology
- First Aid for the USMLE Step 1
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.