Where do basal stem cells proliferate and differentiate to renew the epidermis?

• A. Basal stem cells proliferate, differentiate into keratinocytes, and migrate outward to renew the epidermis.
• B. Keratinocytes themselves proliferate at the surface and migrate inward.
• C. Melanocytes originate from basal cells and replace keratinocytes.
• D. Langerhans cells continuously renew the epidermis.

Answer: (A)

Basal layer stem cells divide to renew the epidermis. Their daughter cells differentiate into keratinocytes and begin migrating upward through the epidermal layers as they mature. This outward movement, with cells gradually keratinizing and finally reaching the surface where they are shed, continuously renews the epidermis. Other epidermal cells like melanocytes and Langerhans cells reside in the epidermis and have distinct roles, but they do not drive renewal through basal proliferation. So the process described—basal stem cells proliferating, differentiating into keratinocytes, and migrating outward to renew the epidermis—best fits how the epidermis is maintained.