An epidermal cell which synthesizes keratin and undergoes a characteristic change as it moves upward from the basal layers of the epidermis to the cornified (horny) layer of the skin. Successive stages of differentiation of the keratinocytes forming the epidermal layers are basal cell, spinous or prickle cell, and the granular cell. [ http://www.ncbi.nlm.nih.gov/pubmed/15749908 http://en.wikipedia.org/wiki/Keratinocyte http://id.nlm.nih.gov/mesh/D015603 http://www.ncbi.nlm.nih.gov/pubmed/19727116 http://www.ncbi.nlm.nih.gov/pubmed/15582983 ]