Which skin layer is a single germinal layer that is mitotically active and provides cells for the layers superficial to it?

• A. Stratum Corneum
• B. Stratum Granulosum
• C. Stratum Spinosum
• D. Stratum Basale

Answer: (B)

The main idea is that the epidermis renews itself from a single, mitotically active layer that sits on the basement membrane and supplies cells to all the layers above. That single, active germinal layer is the one that continuously divides and pushes daughter cells upward to form the other strata.

This layer is the Stratum Basale, also called the germinativum. It consists of a single row (or a very thin layer) of keratinocytes attached to the basement membrane. These cells are capable of mitosis, so they constantly generate new cells that migrate upward to replace those shed from the surface. As they move superficially, they differentiate into the other epidermal layers.

In contrast, the Stratum Spinosum contains several cell layers with desmosomes giving a spiny appearance but is not a single proliferative layer. The Stratum Granulosum has keratohyalin granules and marks the start of keratinization, with only a few layers of cells. The Stratum Corneum is the outermost protective layer of dead, anucleate cells.