Final answer:
Cells die as they are pushed away from the stratum basale due to lack of nutrients and accumulation of keratin. The stratum basale's basal cells divide to create the epidermis's keratinocytes, which move upward, die, and form the protective barrier of the skin.
Step-by-step explanation:
Cells die as they are pushed farther away from the stratum basale because they become too distant from blood vessels to receive nutrients. The stratum basale contains stem cells called basal cells, which divide and produce new keratinocytes.
Two other important cell types in the stratum basale are melanocytes, which produce the pigment melanin, providing color and UV protection, and Merkel cells, which are touch receptors. The loss of access to nutrients supplied by blood vessels, and the accumulation of keratin, eventually lead to cell death and the renewal of the skin's outermost layer.