granulosumkerros

The stratum granulosum, also known as the granular layer, is the third and middle layer of the epidermis. It is located superficial to the stratum spinosum and deep to the stratum lucidum in thick skin, or superficial to the stratum corneum in thin skin. This layer is characterized by the presence of granules within its cells, which are responsible for their name.

The cells in the stratum granulosum, called keratinocytes, begin to flatten and undergo a process of keratinization. This involves the accumulation of keratohyalin granules, which are precursors to the tough, protective protein keratin. Additionally, lamellar granules are released from these cells into the intercellular space. These granules contain lipids that form a barrier, helping to waterproof the skin and prevent water loss.

As the keratinocytes move upwards through the stratum granulosum, they lose their nucleus and organelles, preparing for their eventual transformation into dead, flattened cells in the stratum corneum. The stratum granulosum is typically one to five cell layers thick, depending on the location and thickness of the skin. Its primary role is to continue the process of keratinization and establish the skin's barrier function.