Layers of the Epidermis

Stratum basale (basal layer)

- single row of cells immediately above the dermis

- cells constantly undergoing mitosis to form new cells

- some 10-25% of the cells in this layer are melanocytes

Stratum Spinosum (Spiny layer)

-several layers of cells that contain thick, weblike bundles of intermediate filaments made of a pre- keratin protein

- The cells in this layer appear spiky because when the tissue is prepared, the cells shrink, but their desmosomes hold tight to adjacent cells

- Cells in this layer and the basal layer are the only ones to receive adequate nourishment from diffusion of nutrients from the dermis

Stratum Granulosum (granular layer)

-A thin layer named for the abundant granules its cells contain

-lamellar granules: contain a waterproofing glycolipid that is secreted into the extracellular space

-Keratohyaline granules: help to form keratin in the more superficial layer, at the upper border of this layer, the cells are beginning to die

Stratum lucidum (clear layer)

- present only in thick skin

- A very thin transparent band of flattened, dead keratinocytes with indistinct boundaries

Stratum corneum (horny layer)

- The outermost layer consisting of 20-30 layers of dead, scalelike keratinocytes

- They are constantly being exfoliated and replaced by the division of the deeper cells

Dermis (Papillary Layer)

- The more superficial dermal region composed of areolar connective tissue

- It is very uneven and has fingerlike projections from its superior surface, the dermal papillae, which attach it to the epidermis above

- These projections lie on top of the larger dermal ridges

- Produce the fingerprints- unique patterns of epidermal ridges that remain unchanged throughout life

- Abundant capillary networks in the papillary layer furnish nutrients for the epidermal layers and allow heat to radiate to the skin surface

- The pain and touch receptors are also found here

Reticular layer

- The deepest skin layer

- composed of dense irregular connective tissue and contains many arteries and veins, sweat and sebaceous glads and pressure receptors