(c) Stratum granulosum. Three to five rows of flattened cells
containing keratohyalin, a substance that will finally become keratin, make up this layer
of epidermis. The nuclei of cells are in various stages of degeneration--breaking down
and dying.
(d) Stratum lucidum. This layer is thicker on the palms and soles. The
layer consists of several rows of clear, flat, dead cells that contain droplets of a clear
substance called eleidin. Eleidin eventually becomes keratin.
(e) Stratum corneum. Twenty-five to thirty rows of flat, dead cells that
are completely filled with keratin make up this layer. These cells are shed and replaced
continuously so that roughly every twenty-eight days, this layer is new. It is this layer
with its water-proofing protein keratin which keeps the body from soaking up water like a
sponge. These keratin-filled, dead cells serve as a barrier against light and heat waves,
bacteria, and many chemicals.
c. Dermis.
(1) Composition. The second layer of skin, the dermis or corium, is
sometimes called the true skin. It holds the epidermis in place by connective tissue and
elastic fiber. The dermis is very thick on the palms of the hands and the soles of the
feet but very thin on the eyelids, penis, and scrotum. The dermis contains the following:
numerous blood vessels, nerves, lymph vessels, hair follicles, sweat glands, and
sensory receptors.
(2)
Dermis layers.
(a) Papillary layer. This upper one-fifth of the dermis has small, finger-
like projections called dermal papillae. These projections reach into the concavities
between ridges in the deep surface of the epidermis. This region or layer consists of
loose connective tissue containing fine elastic fibers.
(b) Reticular layer. This layer makes up the rest of the dermis. The
reticular layer consists of dense, irregularly arranged connective tissue which has
interlacing bundles of collagenous and coarse fibers. Between the fibers are adipose
(fat) tissue, hair follicles, nerves, oil glands, and the ducts of sweat glands. The
collagenous and elastic fibers together give the skin strength, extensibility, and
elasticity.
NOTE:
Extensibility is
the ability to
stretch. Elasticity is
the ability to
return to
original
shape after extension or contraction.)
The skin stretches during pregnancy, obesity, or edema. Elasticity allows the skin to
contract after such stretching. If the skin has been stretched severely, small tears may
occur. Initially, the tears are red; they lose the redness but remain visible as silvery
white streaks called striae.
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