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The skin is also a selective barrier: preventing toxic
substances from entering, while permitting the absorption
of certain lubricating oils and medications that can
help prevent certain diseases (heart attacks and motion
sickness), help people avoid smoking and pregnancy,
and help provide hormone replacement. The skin is clearly
a dynamic, versatile and important organ.
Our Skin as a House
It is easier to understand the
normal appearance and function of the skin if we compare
it to a house and the earth on which that house rests.
For example, at its most basic level a house can be
considered to comprise two parts: the house itself and
the earth it rests on. A two-storey house has a basement
and two floors. The basement, or foundation, of the
house rests on the earth. The house itself consists
of bricks and a roof. The bricks are joined together
by cement.
The skin, like a house, is also
divided into two parts: the outer, thinner portion called
the epidermis (which we can think of as our house) and
the inner, thicker layer called the dermis (which we
can think of as the ground or earth). Just as a house
rests on the earth for stability, the epidermis rests
on top of the dermis.
If the house consists of
bricks, cement and a roof, the skin also has "bricks,"
"cement" and a "roof." The outer
layer of the skin (epidermis) is composed of so-called
"bricks," which we call skin cells or keratinocytes.
Just as bricks are joined using cement, skin cells or
keratinocytes are joined together by small attachments
called desmosomes. As cement keeps the bricks together
as a continuous layer, desmosomes join the skin cells
as a continuous layer.
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