Final answer:
The stratum granulosum marks the transition in the epidermis where keratinocytes begin to die off, contributing to the formation of the skin's outer protective layers by accumulating large amounts of keratin and keratohyalin, and releasing lipids that help create a waterproof barrier.
Step-by-step explanation:
The transition that the stratum granulosum marks is crucial in the process of keratinization, where keratinocytes undergo physical and biochemical changes to form the protective outer layers of the skin. In the stratum granulosum, the cells become flatter, their cell membranes thicken, and they start to generate large amounts of the proteins keratin and keratohyalin. These changes lead to the cells' granular appearance and prepare them to form the next layers of skin, the stratum lucidum and stratum corneum, along with the accessory structures of hair and nails.In this layer, keratinocytes also release lipids that form a barrier in the epidermis, contributing to the skin's waterproof properties. As the keratinocytes become too far removed from the blood supply, they begin to die, leaving behind the proteins and cell membranes that will continue to provide protection and support to the skin's integrity. The stratum granulosum is therefore where cells transition from living tissue to become part of the dead, protective barrier that is essential for the skin's functions.