Which tissue forms most of the epidermis, and what distinguishes its outermost layer?

• A. Simple cuboidal epithelium; outer surface is keratinized
• B. Stratified squamous epithelium; Outer layer keratinized, consisting of dead, keratin-filled cells
• C. Pseudostratified epithelium; Outer layer is keratinized
• D. Simple squamous epithelium; Outer surface is mucous-secreting

Answer: (B)

The tissue that forms most of the epidermis is stratified squamous epithelium. This means multiple layers of flat, tightly packed cells that provide strong protection against abrasion. As cells originate in the deepest layer and move outward, they become flatter, fill with keratin, and eventually die. Their remnants create the outermost keratinized layer, composed of dead, keratin-filled cells, which forms a tough, waterproof barrier. This keratinized surface is what helps prevent water loss and protects against friction, especially on the skin’s outermost areas like the palms and soles. In contrast, non-keratinized epithelia line moist surfaces (such as the mouth and esophagus) where cells retain nuclei and stay alive.