Which statement correctly contrasts keratinized and non-keratinized stratified squamous epithelium?

• A. Keratinized epithelium has surface keratin-filled dead cells; non-keratinized lacks this layer and remains moist.
• B. Keratinized epithelium lacks a surface keratin layer; non-keratinized has a surface keratin layer.
• C. Keratinized epithelium is found in the oral mucosa; non-keratinized forms the epidermis of the skin.
• D. Keratinized epithelium is only found in glands; non-keratinized is only found in blood vessels.

Answer: (A)

The main concept is whether the surface of stratified squamous epithelium has a keratin-filled layer. In keratinized tissue, the outermost cells are dead and packed with keratin, forming a tough, dry protective layer that you mainly find in the skin’s epidermis. In non-keratinized tissue, the surface cells retain their nuclei and cytoplasm and there isn’t a keratin-filled layer, so the surface remains moist and flexible to protect mucosal linings like those in the mouth, esophagus, and vagina. This is why the statement describing surface keratin-filled dead cells on the keratinized side and a lack of that layer with moist surfaces on the non-keratinized side best captures the contrast.