Calluses or corns are thickened areas of epidermis. They are the result of accelerated multiplication by stem cells. You know what happens in epidermal strata, so you know that this stem cell division starts in the
stratum lucidum
stratum basale
stratum corneum
stratum granulosum
The Correct Answer and Explanation is:
Correct Answer: stratum basale
Explanation (
Calluses and corns are thickened areas of the epidermis that form as a protective response to repeated friction or pressure. This thickening is due to an increased production of keratinocytes, the predominant cell type in the epidermis. The process begins at the stratum basale, which is the deepest layer of the epidermis and the site where stem cells reside.
The stratum basale (also called the basal layer) consists of a single row of cuboidal to columnar basal cells that are mitotically active. These basal stem cells divide continuously to produce new keratinocytes. As new cells are formed, older cells are pushed upward through the successive layers of the epidermis. These layers include, from deepest to most superficial: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (only present in thick skin like the palms and soles), and stratum corneum.
In areas of frequent friction (such as the soles of the feet or the palms of the hands), the basal stem cells increase their rate of division in response to mechanical stress. This leads to an accumulation of cells in the upper layers of the epidermis, especially in the stratum corneum, where dead keratinocytes accumulate to form the thickened surface characteristic of calluses and corns. However, this thickening originates at the stratum basale, where the cell production begins.
The stratum corneum consists of dead, flattened cells and cannot generate new cells. Similarly, the stratum granulosum and stratum lucidum are transitional layers involved in keratinization but not in cell division. Only the stratum basale has stem cells capable of undergoing mitosis to renew and repair the epidermis.
Thus, the development of calluses and corns ultimately traces back to the stratum basale, where stem cell activity is initiated in response to external stress.
