Final answer:
The stratum granulosum contains keratinocytes that are filled with keratin and keratohyalin, making the layer appear grainy. These cells also release lipids for the skin's lipid barrier and disintegrate, leading to the formation of outer skin layers and hair and nail structures.
Step-by-step explanation:
The stratum granulosum is a grainy layer in the skin where keratinocytes undergo significant changes. In this layer, keratinocytes become flatter, their cell membranes thicken, and they accumulate large amounts of the proteins keratin and keratohyalin. These proteins are stored as lamellar granules within the cells, contributing to the grainy appearance of this skin layer. Keratinocytes in the stratum granulosum also release lipids that contribute to the lipid barrier of the epidermis. Eventually, the nuclei and other cell organelles in these keratinocytes disintegrate as the cells die, which is an essential process for the formation of the outer skin layers such as the stratum lucidum and the stratum corneum, as well as for the accessory structures of hair and nails.