Keratinocytes also play a role in immune responses through the production of a variety of cytokines. The skin is not completely impermeable. Compounds can pass through intact skin. This permeability of the skin is used for the delivery of topical therapeutic agents used in the treatment of certain skin diseases, and also for delivery of medication used in the treatment of systemic diseases. Examples of percutaneous delivery include scopolamine, used for treatment of motion sickness, nitroglycerine for angina pectoris and estrogen for postmenopausal symptoms.
Melanocytes are cells derived from the neural crest.
They migrate early during embryonic development and pass through the dermal mesenchyme to reside in the basal layer of the epidermis. There is approximately one melanocyte for every 10 basal keratinocytes. Unlike keratinocytes, melanocytes rarely divide and normally do not migrate upwards. Melanocytes have long, dendritic processes that reach the upper and lower layers of the epidermis. Through these dendrites melanocytes transfer melanosom to the keratinocytes.