Cells of the Epidermis:
- Keratinocytes:
- Origin and Location: Derived from ectoderm, present in all layers of the epidermis (90-95% of all epidermal cells).
- Characteristic Features: Rich in intermediate filaments called keratin, providing mechanical strength. Basal layer keratinocytes divide and generate the upper layer.
- Melanocytes:
- Origin and Location: Derived from neural crest, present in the stratum basale.
- Characteristic Features: Synthesize melanin in granules (melanosomes) transferred to keratinocytes via dendrites. Each melanocyte transfers melanin to approximately 36 keratinocytes, forming the Epidermal Melanin Unit.
- Merkel Cells:
- Origin and Location: Derived from neural crest, present in the stratum basale (rete ridges).
- Characteristic Features: Also known as touch cells or Haarsheiban cells. They are slow-adapting touch receptors.
- Langerhans Cells:
- Origin and Location: Derived from bone marrow, migrate to the epidermis.
- Characteristic Features: Dendritic antigen-presenting cells (APCs) with rod-shaped or tennis racket-shaped granules seen on electron microscopy. Immunohistochemical markers include CD1a, CD207 (Langerin), and S100.