Skin is the body's largest
organ. About six pounds of skin cover eighteen
square feet on an average adult. The top layer
of skin is called the epidermis. It protects
the underlying skin layers from the outside environment
and contains cells that make keratin, a substance
that waterproofs and strengthens the skin.
The
epidermis also has cells that contain melanin,
the dark pigment that gives skin its color. Other
cells in the epidermis allow us to feel the sensation
of touch and provide the body with immunity against
foreign invaders like germs and bacteria. The
very bottom layer of the skin is the hypodermis.
It contains the fat cells, or adipose tissue,
that insulate the body and help it conserve heat.
The layer between the epidermis and the hypodermis
is the dermis. It contains the cells that give
skin strength, support, and flexibility.
As a
person ages, the cells in the dermis lose their
strength and flexibility, causing the skin to
lose its youthful appearance. Located in the
dermis are sensory receptors. They allow the
body to receive stimulation from the outside
environment and experience pressure, pain, and
temperature.
Small blood vessels provide the
skin with nutrients, and remove its waste products.
Sebaceous glands produce the oil in the skin,
which keeps it from drying out. The oil from
the sebaceous glands also helps to soften hair
and kill bacteria that get in the skin's
pores. These oil glands are all over the body,
except on the palms of the hands and the soles
of the feet.
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