What significant change happens in the stratum granulosum?

The stratum granulosum is a critical layer in the epidermis, known for its role in the keratinization process. Within this layer, older skin cells begin to undergo significant changes that contribute to the skin’s protective barrier. One of the key events that occurs here is the development of keratin and keratohyalin granules, which contain proteins essential for creating the tough, protective outer layer of the skin.

As these cells are moving up from the deeper layers of the epidermis, they start to synthesize proteins that form keratin: a fibrous structural protein that provides strength and resilience to the skin. This process is crucial because keratin is what enables the skin to act as a barrier against environmental stressors, pathogens, and water loss. The presence of these granules is a defining characteristic of the stratum granulosum and sets the stage for the subsequent layers, where cell maturation and eventual shedding occur.

While younger cells do form new layers of skin in deeper layers, the transformative process of protein and keratin precursor development specifically marks the stratum granulosum. This makes it essential for the understanding of how the skin maintains its integrity and function.