Final answer:
In the stratum granulosum, keratinocytes produce keratin and keratohyalin, leading to a grainy appearance and forming a lipid barrier that aids in water retention. These cells eventually die, contributing to the formation of upper skin layers and accessory structures.
Step-by-step explanation:
The Role of the Stratum Granulosum in Skin
In the stratum granulosum, significant changes occur to the keratinocytes, which have been pushed up from the stratum spinosum. The cells in this layer, which are three to five layers deep, flatten out and their cell membranes thicken. They produce large quantities of keratin, a fibrous protein, and keratohyalin, which forms lamellar granules within the cells. This accumulation gives the layer a grainy appearance and constitutes the bulk of the keratinocyte mass in the stratum granulosum. Subsequently, the nuclei and other cell organelles disintegrate as the cells die off, leaving behind keratin, keratohyalin, and the cell membranes that are integral to forming the stratum lucidum, the stratum corneum, and the accessory structures such as hair and nails.
Additionally, keratinocytes in this layer release lipids that form a lipid barrier in the epidermis, crucial for preventing water loss and making the skin water-resistant. This is of particular importance because the cells in the stratum granulosum start to die, mainly due to their increased distance from the blood vessels in the dermis, which deprives them of necessary nutrients.