<P> The epidermis contains no blood vessels, and cells in the deepest layers are nourished almost exclusively by diffused oxygen from the surrounding air and to a far lesser degree by blood capillaries extending to the outer layers of the dermis . The main type of cells which make up the epidermis are Merkel cells, keratinocytes, with melanocytes and Langerhans cells also present . The epidermis can be further subdivided into the following strata (beginning with the outermost layer): corneum, lucidum (only in palms of hands and bottoms of feet), granulosum, spinosum, basale . Cells are formed through mitosis at the basale layer . The daughter cells (see cell division) move up the strata changing shape and composition as they die due to isolation from their blood source . The cytoplasm is released and the protein keratin is inserted . They eventually reach the corneum and slough off (desquamation). This process is called "keratinization". This keratinized layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and pathogens out, making skin a natural barrier to infection . </P> <P> The epidermis contains no blood vessels, and is nourished by diffusion from the dermis . The main type of cells which make up the epidermis are keratinocytes, melanocytes, Langerhans cells and Merkel cells . The epidermis helps the skin to regulate body temperature . </P> <P> Epidermis is divided into several layers where cells are formed through mitosis at the innermost layers . They move up the strata changing shape and composition as they differentiate and become filled with keratin . They eventually reach the top layer called stratum corneum and are sloughed off, or desquamated . This process is called keratinization and takes place within weeks . The outermost layer of the epidermis consists of 25 to 30 layers of dead cells . </P> <P> Epidermis is divided into the following 5 sublayers or strata: </P>

What type of tissue makes up the most external skin region