During epidermal progression, what is the major protein that cells accumulate as they move toward the surface?

• A. Collagen
• B. Elastin
• C. Melanin
• D. Keratin

Answer: (D)

As epidermal cells migrate from the deeper layers toward the surface, they accumulate keratin, a tough, fibrous protein that provides mechanical strength. This keratinization process fills the cells with keratin filaments, and the cells eventually lose their nuclei and organelles to form the dead, keratin-rich cells of the outermost layer, creating the protective barrier of the stratum corneum. Collagen and elastin belong to the dermal connective tissue and support tissue structure, not the migrating epidermal cells. Melanin is pigment produced by melanocytes and contributes to skin color, but it is not the main protein these cells accumulate as they rise.