The skin se n se s th e o u tsid e • Figure 4.8
Sensory receptors within the skin
provide information about the
outside environment through touch,
temperature, pressure, and pain.
Nociceptors
are free nerve endings that
sense pain rapidly. Other free nerve endings
sense tickle, itch, and some touch.
Epidermis
Dermis
Subcutaneous layer
Merkel (tactile) disc
slowly senses touch
near surface.
Meissner corpuscle
rapidly senses touch
near surface.
Ruffini corpuscle
slowly senses stretching
in deep layers of skin.
Hair
root plexus
senses movement
of the hair.
Pacinian corpuscle
senses pressure.
The skin is one of our connections to the outside
world. Its specialized nerve receptors sense pressure, pain,
changes in temperature, and things we touch. These re-
ceptors include mechanoreceptors, Meissner corpuscles,
Pacinian corpuscles, thermoreceptors, and pain recep-
tors called nociceptors (Figure 4.8).
The skin absorbs and excretes substances through its
surface. Transdermal patches have been used to deliver
various drugs such as nicotine for quitting smoking and
estrogen derivatives for birth control. Chemicals such as
those found in nail polish removers and cleaning prod-
ucts can also absorb readily through the skin and into the
blood. Some of these products can be quite toxic if they en-
ter the blood. In contrast, through sweat, the skin excretes
water, small amounts of carbon dioxide, salts, ammonia,
and urea.
The skin plays an important role in calcium homeosta-
sis within your body. Your skin produces vitamin D when
exposed to UV radiation. Vitamin D is converted to an ac-
tive form by reactions in the liver and kidney. Just 5 to
30 minutes of sunlight exposure twice a week can provide
you with an adequate amount of vitamin D. As you will
see later, vitamin D gets processed further by other organs
and ultimately acts in the intestines to assist absorption of
calcium and phosphorus.
All of the skin’s many functions may be disrupted if the
skin is severely damaged. One source of damage is a burn,
which is damage to proteins in tissues caused by heat, elec-
tricity, radiation, or corrosive chemicals, and can vary in their
severity (Figure 4.9). The more tissue gets damaged, the
less likely that the skin will be able to repair itself (see
What a
Health Provider Sees).
Some burns are
accompanied by edema. Severely
and extensively burned tissue can be
life threatening due to the following:
Because skin receives a large percentage of blood flow,
there are several circulatory consequences that lead to
fluid loss and shock:
• Large loss of water, plasma, and proteins can result in
edema; and hypovolemia (low blood volume), which
can result in a sudden drop of blood pressure
• Reduced blood pressure, which can result in reduced
circulation of blood
• Decreased urine production
Microbial infection can occur because of the absence of
the skin’s protective covering and inability of immune
cells to reach the invaders due to changes in blood
pressure and blood flow.
edema
(e-DE-ma) An
abnormal accumula-
tion of interstitial fluid.
102
CHAPTER 4
The Integumentary System
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