Cells and Layers of The Epidermis

Stratum Basale

1. Consists mainly of a single layer of cuboidal to low columnar stem cells and keratinocytes resting on the basement membrane. Scattered among these are the melanocytes, tacile cells and stem cells.

Stratum Spinosum

2.Consists of several layers of keratinocytes. In most skin this is the thickest layer but in thicker skin it is exceeded by the stratum corneum. The deepest cells of this layer remain capable of mitosis but as they're pushed farther up they cease dividing. The higher up you look the flatter they appear. Bound to each other by tight junctions and desmosomes.

Stratum Granulosum

3. Consists of 3-5 layers of flat keratinocytes-more in thick skin. These contain course dark keratohyalin granules that give the layer it's name.

Stratum Lucidum

4. Thin zone superficial to the stratum granulosum seen only in thick skin. Here the keratinocytes are densely packed with a clear protein named eleidin. The cells have no nuclei or other organelles. This zone has a pale featureless appearance with indistinct cell boundaries.

Stratum Corneum

5. Consists of up to 30 layers of dead, scaly, keratinized cells that form a durable surface layer. Resistant to abrasion, penetration and water loss.

Dendritic Cells

Found in the stratums spinosum and stratum granulosum of the. They are immune cells that originate in the bone marrow but migrate to the epidermis and epithelia of the oral cavity esophogus and vagina. 800 cells per square inch in epidermis they stand guard against pathogens that penetrate skin.

Melanocytes

Occur only in stratum basale amid the stem cells and deepest keratinocytes. They synthesize the borwn to black pigmentt melanin. They have branching processes that spread among the keratinocytes and continually shed melanin containing fragments from their tips. These are phagocytized by sunny side/apical keratinocytes which accumulate melanin granules.

Tactile cells

Relatively few in number they are receptors for touch they too are found in the basal layer of the epidermis and are associated with underlying dermal nerve fibe

Keratinocytes

The great majority of epidermal cells. Named for their role in synthesizing Keratin. In ordinary histological specimens nearly all visible epidermal cells are keratinocytes

Stem Cells

Undifferentiated cells that divide and give rise to the keratinocytes. they are found only in the deepest layer of the epidermis, the stratum basale.