Which layer of the skin is characterized by grainy cells?

The stratum granulosum is the layer of the skin that is characterized by the presence of "grainy" cells. This layer is located above the stratum spinosum and beneath the stratum lucidum in thick skin, or directly beneath the stratum corneum in thinner skin. The "grainy" appearance comes from the keratinocytes within this layer, which begin to undergo a process of keratinization.

In the stratum granulosum, cells produce keratohyalin granules, which are rich in proteins that aid in the aggregation of keratin filaments, leading to a tough and protective outer layer. The cells also begin to lose their nuclei and organelles as they progress toward the surface of the skin, which contributes to the grainy texture and appearance.

This layer plays a crucial role in forming a water barrier that helps prevent dehydration and protects the underlying layers of the skin. Understanding the specific characteristics of the stratum granulosum enhances the comprehension of skin physiology and histology, particularly in relation to the processes of skin health and barrier function.