183
CHAPTER SIX
Integumentary System
PRACTICE
21
Why is regulation of body temperature so important?
22
How is body heat produced?
23
How does the body lose excess heat?
24
How does the skin help regulate body temperature?
25
What are the dangers of hypothermia?
6.5
HEALING OF WOUNDS
AND BURNS
Infl
ammation
is a normal response to injury or stress. Blood
vessels in affected tissues dilate and become more perme-
able, allowing fluids to leak into the damaged tissues.
Infl amed skin may become reddened, swollen, warm, and
painful to touch. However, the dilated blood vessels provide
the tissues with more nutrients and oxygen, which aids heal-
ing. The speciF c events in the healing process depend on the
nature and extent of the injury.
Cuts
If a break in the skin is shallow, epithelial cells along its mar-
gin are stimulated to divide more rapidly than usual. The
newly formed cells F
ll the gap.
If an injury extends into the dermis or subcutaneous
layer, blood vessels break, and the escaping blood forms a
clot in the wound. A clot consists mainly of a F
brous pro-
tein (F
brin) that forms from another protein in the plasma,
blood cells, and platelets trapped in the protein fibers.
Tissue fl
uids seep into the area and dry. The blood clot and
the dried fl
uids form a
scab
that covers and protects under-
lying tissues. Epithelial cells proliferate beneath the scab,
bridging the wound. Before long, F
broblasts migrate into
the injured region and begin secreting collagenous F
bers
that bind the edges of the wound. Suturing or otherwise
closing a large break in the skin speeds this process. In
addition, the connective tissue matrix releases
growth fac-
tors
that stimulate certain cells to divide and regenerate the
damaged tissue.
As healing continues, blood vessels extend beneath the
scab. Phagocytic cells remove dead cells and other debris.
Eventually, the damaged tissues are replaced, and the scab
sloughs off. If the wound is deep, extensive production of
collagenous F bers may form an elevation above the normal
epidermal surface, called a
scar.
In large, open wounds, healing may be accompanied
by formation of small, rounded masses called
granulations
that develop in the exposed tissues. A granulation consists
of a new branch of a blood vessel and a cluster of collagen-
secreting F
broblasts that the vessel nourishes. In time, some
of the blood vessels are resorbed, and the F
broblasts move
away, leaving a scar largely composed of collagenous F
bers.
Figure 6.13
shows the stages in the healing of a wound.
If body temperature
continues to drop,
control center signals
muscles to contract
involuntarily.
too high
too low
Normal body
temperature
37
°
C (98.6
°
F)
Control center
Hypothalamus
detects the deviation
from the set point and
signals effector organs.
Control center
Hypothalamus
detects the deviation
from the set point and
signals effector organs.
Stimulus
Body temperature rises
above normal.
Effectors
Dermal blood vessels
dilate and sweat glands
secrete.
Response
Body heat is
lost to surroundings,
temperature drops toward
normal.
Effectors
Dermal blood
vessels constrict
and sweat glands
remain inactive.
Effectors
Muscle
activity
generates
body heat.
Response
Body heat is conserved,
temperature rises toward normal.
Stimulus
Body temperature
drops below normal.
Receptors
Thermoreceptors
send signals to the
control center.
Receptors
Thermoreceptors
send signals to the
control center.
FIGURE 6.12
Body temperature regulation is an example of
homeostasis.
Hypothermia is intentionally induced during certain surgical pro-
cedures involving the heart, brain, or spinal cord. In heart surgery,
body temperature may be lowered to between 78°F (26°C) and 89°F
(32°C), which lowers the body’s metabolic rate so that less oxygen is
required. Hypothermia for surgery is accomplished by packing the
patient in ice or by removing blood, cooling it, and returning it.
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