Skin, Hair, and Nails: The Basics |
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Skin
Your skin consists of several different types of tissue that
perform a variety of essential functions for your body. Skin helps
regulate your body temperature by sweating in response to heat and
decreasing blood flow to the skin in response to cold (thereby
keeping the heat deeper inside the body).
The skin’s pigment shields your body from dangerous
ultraviolet rays. Nerve endings in the skin pick up and relay
information about the surrounding environment to your brain, where
it is translated into the sensations of touch, pressure, heat, or
cold. Cells known as Langerhans cells are part of the immune system
and help the skin fight infection. The skin also makes vitamin D
from sunlight, which is essential in making bones strong.
Perhaps most important, your skin forms a physical barrier to
injury and infection. The most significant part of this barrier is
the top layer of skin, called the epidermis. At the very top of the
epidermis, dead cells called keratinocytes (which contain a
chemical called keratin) form a soft, protective sheet. The dead
cells come from younger, living cells in the lower part of the
epidermis, where they are constantly produced.
Copyright 1999 © by President and Fellows of Harvard College
Reprinted with permission from the Harvard Medical School Family Health Guide, Simon & Schuster 1999. Art copyright © Harriet R. Greenfield, Newton, Mass.
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