Which form of stratified squamous epithelium forms the epidermis of the skin?

• A. Nonkeratinized stratified squamous epithelium
• B. Keratinized stratified squamous epithelium
• C. Simple squamous epithelium
• D. Transitional epithelium

Answer: (B)

The epidermis is formed by keratinized stratified squamous epithelium. Keratinization means the cells at the surface accumulate keratin, lose their nuclei, and become dead, flat, waterproof cells. This creates the outer stratum corneum that resists abrasion and reduces water loss, providing a tough, protective barrier for the skin. As cells migrate upward from the deeper layers, they keratinize and are eventually shed. In contrast, nonkeratinized stratified squamous epithelium lines moist internal surfaces (like the mouth and esophagus) and keeps surface cells living and moist, which isn’t suitable for the dry, abrasive exterior of the skin. Simple squamous epithelium is a single layer used for diffusion and filtration, and transitional epithelium lines organs that stretch, such as the bladder.