​What is Dermatology - How many layers does the epidermis have? How are they set up?

​What is Dermatology - How many layers does the epidermis have? How are they set up?

The basal cell layer, spiny cell layer, granular cell layer, and cornified layer are the four layers of the epidermis.
Columnar or cuboidal cells make up the basal cell layer (stratum basalis), which is in direct contact with the basement membrane, which separates the dermis from the epidermis. Because the germinative cells are found in the basal cell layer, there may be some mitoses present.

The keratinocytes differentiate as they migrate nearer the skin surface and become "cornified" in the three layers above the basal cell layer, which are histologically unique. The spiny cell layer (stratum spinosum) is located just above the basal cell layer and is named for the high concentration of desmosomes and keratin filaments that give the cells their characteristic "spiny" look . The granular cell layer (stratum granulosum) sits above the spiny layer. Keratohyalin granules are generated in this layer and bind to keratin filaments (tonofilaments) to form enormous electron-dense masses inside the cytoplasm, giving it a "granular" appearance.

The cornified layer (stratum corneum) is the outermost layer, where keratinocytes abruptly lose all of their organelles and nuclei. Within the keratinocytes, the keratin filaments and keratohyalin granules form an amorphous mass that becomes elongated and flattened, generating a lamellar array of "corneocytes." Desmosome remnants (dense bodies) and a "cementing substance" secreted into the intracellular space by organelles termed Odland bodies hold the corneocytes together.