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Stratum Spinosum
The stratum spinosum is the next layer up and is sometimes considered to be part of the stratum
germinativum. It includes cells that have absorbed melanin to distribute pigmentation to other
cells. The cells then become irregularly shaped and have a "spiny" appearance.
Stratum Granulosum
The next layer is the stratum granulosum. In this layer the cells become more regularly shaped and
look like many tiny granules. This layer of the epidermis gets its name from these granules. These
granules (almost dead cells) are on their way to the surface of the skin to replace cells that are shed
from the stratum corneum.
Stratum Lucidum
On the palms of the hands and the soles of the feet only, (where there are no hair follicles),
there is another skin layer that is called the stratum lucidum. The cells in this layer are even
more flattened and transparent (clear). They are called squamous (SQUAW-mus) cells due to their
flat, scale-like appearance, thus making the skin thickest on palms of hands and soles of feet.
Stratum Corneum
The uppermost layer, the stratum corneum sometimes called the horny layer, is the toughest layer
of the epidermis and is composed of keratin protein cells that are continually shed and continually
replaced by new cells from below. Unlike the hard keratin found in nails and hair, the keratin pro-
duced by the skin remains soft throughout the keratinization and shedding process. The stratum
corneum acts as a protective layer for the layers below it. It protects the skin's
moisture balance by acting as a barrier to moisture loss. It, in turn, is protected
by an acid mantle, a mixture of oil, secreted by sebaceous oil glands, and water
secreted by sweat glands. The pH of the acid mantle averages 4.5 to 5.5.
The entire epidermis protects the dermis and the subcutaneous division below the
skin. Since the skin cells are constantly being sloughed off at the stratum
corneum, the replacement of the cells is a continuous process.
Dermis
The dermis layer is made up of connective tissues. Connective tissues are composed of a semifluid
substance containing collagen protein and elastin fibers, both of which lend support to the epider-
mis and give the skin its elastic quality. Collagen protein fibers are strong and flexible while the
elastin fibers are soft and pliable. It is in this layer that the collagen and elastin fibers deteriorate,
causing the skin to sag and wrinkle during the aging process. Also found in
the dermis are the sweat glands called sudoriferous (soo-dohr-IF-er-us)
glands, oil glands called sebaceous (sih-BAY-shus) glands, sensory nerve
endings and receptors, blood vessels, arrector pili muscles and a major por-
tion of each hair follicle. Remember that hair is an appendage of the skin,
as are the nails and sweat and oil glands.
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THE STUDY OF SKIN
The dermis is
also called the
`true skin' or
corium
(KOH-ree-um)
.
"According to some authorities,
you have up to a hundred
trillion cells in the body!
You shed some five billion
cells daily!"
