The epidermis is divided into five layers. From outside to inside (dermis). The stem cells are located in the stratum basale and migrate outwards in their differentiation process
- Stratum corneum: The outmost layer, made of dead keratinocytes with a layer of protein around them (they have undergone keratinization)
- Stratum lucidum: Also dead keratinocytes (there is no real distinction here other than that the poor keratinocytes have died but have not finished the keratinization process)
- Stratum granulosum: the keratinocytes are still on the move, by this point they have kertahyalin granules
- Stratum spinosum: the keratinocytes migrating up, they have nice oval nuclei
- Stratum basale: Single layer of proliferating columnar keratinocytes, melanocytes (pigmented cells) and Merkel cells (mechanoreceptors) also live here
Of note, Langerhans cells, which are specialized antigen-presenting cells are present in all layers of the epidermis but are mostly in the stratum spinosum.