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Your skin is an organ that contains many specialized cells and
structures. It functions as a protective barrier that interfaces
with an often-hostile environment and is also involved in
maintaining the proper temperature for the body to function well. It
gathers sensory information from the environment, and plays an
active role in the immune system protecting us from disease.
Understanding how the skin can function in these many ways starts
with understanding the structure of the 3 layers of skin - the
epidermis, dermis, and subcutaneous tissue.
Epidermis
The epidermis is the outer layer of skin. The thickness of the
epidermis varies in different types of skin. It is the thinnest on
the eyelids at .05 mm and the thickest on the palms and soles at 1.5
mm. The epidermis contains 5 layers. From bottom to top the layers
are named stratum basale, stratum spinosum, stratum granulosum,
stratum licidum, and stratum corneum. The bottom layer, the stratum
basale, has cells that are shaped like columns. In this layer the
cells divide and push already formed cells into higher layers. As
the cells move into the higher layers, they flatten and eventually
die. The top layer of the epidermis, the stratum corneum, is made of
dead, flat skin cells that shed about every 2 weeks.
There are three types of specialized cells in the epidermis. The
melanocyte produces pigment (melanin), the Langerhans' cell is the
frontline defense of the immune system in the skin, and the Merkel's
cell's function is not clearly known.
Dermis
The dermis also varies in thickness depending on the location of the
skin. It is .3 mm on the eyelid and 3.0 mm on the back. The dermis
is composed of three types of tissue that are present throughout -
not in layers. The types of tissue are collagen, elastic tissue, and
reticular fibers. The two layers of the dermis are the papillary and
reticular layers. The upper, papillary layer, contains a thin
arrangement of collagen fibers. The lower, reticular layer, is
thicker and made of thick collagen fibers that are arranged parallel
to the surface of the skin. The dermis contains many specialized
cells and structures. The hair follicles are situated here with the
erector pili muscle that attaches to each follicle. Sebaceous (oil)
glands and apocrine (scent) glands are associated with the follicle.
This layer also contains eccrine (sweat) glands, but they are not
associated with hair follicles. Blood vessels and nerves course
through this layer. The nerves transmit sensations of pain, itch,
and temperature. There are also specialized nerve cells called
Meissner's and Vater-Pacini corpuscles that transmit the sensations
of touch and pressure.
Subcutaneous Tissue
The subcutaneous tissue is a layer of fat and connective tissue that
houses larger blood vessels and nerves. This layer is important in
the regulation of temperature of the skin itself and the body. The
size of this layer varies throughout the body and from person to
person.
The skin is a complicated structure with many functions. If any of
the structures in the skin are not working properly, a rash or
abnormal sensation may result. |
