Which layer of the epidermis contains keratin-filled granules?

The layer of the epidermis that contains keratin-filled granules is indeed the stratum granulosum. This layer is crucial in the process of keratinization, where keratinocytes begin to lose their nuclei and cytoplasmic organelles, signifying their transition from active cells to dead, flattened cells filled primarily with keratin. The granules present in this layer, known as keratohyalin granules, play a vital role by aggregating keratin filaments, which contributes to the barrier function of the skin and the overall water retention capability.

In comparison, the stratum lucidum is found only in thick skin areas (like the palms and soles) and provides an additional layer of protection but does not contain granules; rather, it consists of dead cells filled with eleidin, a clear protein. The stratum germinativum is where new skin cells are generated through mitosis, located beneath the granulosum, and lacks the keratin-filled granules characteristic of the stratum granulosum. The stratum corneum, being the outermost layer of the epidermis, consists mostly of dead, keratinized cells that have already completed the process of keratinization, thus they do not