Epidermis

The epidermis contains no blood vessels, and cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the dermis. The main type of cells which make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells. 

Cells are formed through mitosis at the basale layer. The daughter cells move up the strata, changing shape and composition. They eventually reach the stratum corneum and slough off (desquamation). This process is called keratinization and takes place within about 27 days. The keratinized layer of skin acts like a shield and protects the human body.