What is the histological hallmark of keratinization?

• A. Presence of a keratinized surface layer, the stratum corneum, on the epithelium.
• B. The basement membrane anchors epithelia to underlying connective tissue.
• C. Goblet cell mucous secretion.
• D. Simple squamous epithelium specialized for diffusion.

Answer: (A)

Keratinization creates a tough, protective outer surface by producing keratin and forming a layer of dead, keratin-filled cells. The histological hallmark is a keratinized surface layer, the stratum corneum, on the epithelium. In this outer layer, cells have become enucleated and packed with keratin, providing a durable, waterproof barrier that reduces water loss and protects against friction. This contrasts with non-keratinizing epithelia, which lack this dead, keratin-rich surface. For example, goblet cells secrete mucus in mucosal epithelia, and simple squamous epithelia are specialized for diffusion, not for forming a keratinized outer surface.