What layer of the epidermis marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata?

The layer of the epidermis that marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata is the Stratum Granulosum. This layer is significant because it plays a crucial role in the process of keratinization, where keratinocytes begin to die and lose their nuclei, becoming more flattened and packed with keratin.

The Stratum Granulosum contains keratin granules, which contribute to the protective barrier function of the skin. As cells move up from the deeper layers, they undergo changes that prepare them for eventual shedding from the surface. In contrast to the active cell division that occurs in the Stratum Germinativum (the deepest layer), the Stratum Granulosum is where the cells begin the transition to the outermost layer, ultimately becoming the dead, flattened cells found in the Stratum Corneum. This transition is essential for maintaining skin integrity and barrier function.