Chapter 5
The Integumentary System
167
5
injuries increases. Te lubricating substances produced by the
skin glands that make young skin so sof become deficient. Skin
becomes dry and itchy, although people with naturally oily skin
seem to postpone this dryness until later in liFe. Elastic fibers
clump, and collagen fibers become Fewer and stiffer. Te subcu-
taneous Fat layer diminishes, leading to the intolerance to cold
so common in elderly people. Additionally, declining levels oF
sex hormones result in similar Fat distribution in elderly men
and women.
Te decreasing elasticity oF the skin, along with the loss oF
subcutaneous tissue, inevitably leads to wrinkling. Decreas-
ing numbers oF melanocytes and dendritic cells enhance the
risk and incidence oF skin cancer in this age group. As a rule,
redheads and Fair-skinned individuals, who have less melanin
to begin with, show age-related changes more rapidly than do
those with darker skin and hair.
By age 50, the number oF active hair Follicles has declined by
two-thirds and continues to Fall, resulting in hair thinning. Hair
loses its luster in old age, and the delayed-action genes responsi-
ble For graying and male pattern baldness become active.
Although there is no known way to avoid skin aging, one
oF the best ways to slow the process is to shield your skin From
both the UVA (aging rays) and UVB (rays that burn) oF the sun.
Aged skin that has been protected From the sun, while it grows
thinner and loses some elasticity, still remains unwrinkled and
unmarked. Wear protective clothing and apply sunscreens or
sunblocks with a sun protection Factor (SP±) oF 15 or higher.
Remember, the same sunlight that produces that Fashionable
tan also causes the sagging, blotchy, wrinkled skin oF old age
complete with pigmented “liver spots.” Much oF this havoc is
due to UVA activation oF enzymes called matrix metallopro-
teinases, which degrade collagen and other dermal components.
A drug called tretinoin, related to vitamin A, inhibits these en-
zymes and is used in some skin creams to slow photo-aging.
Good nutrition, plenty oF fluids, and cleanliness may also delay
the process.
Check Your Understanding
29.
What is the source of vernix caseosa that covers the skin of
the newborn baby?
30.
What change in the skin leads to cold intolerance in the
elderly?
31.
How does UV radiation contribute to skin wrinkles?
For answers, see Appendix H.
Te skin is only about as thick as a paper towel—not too im-
pressive as organ systems go. Yet, when it is severely damaged,
nearly every body system reacts. Metabolism accelerates or may
be impaired, immune system changes occur, bones may sofen,
the cardiovascular system may Fail—the list goes on and on.
On the other hand, when the skin is intact and perForming its
Functions, the body as a whole benefits.
System Connections
on
p. 168 summarizes homeostatic interrelationships between the
integumentary system and other organ systems.
27.
The healing of burns and epidermal regeneration is usually
uneventful unless the burn is a third-degree burn. What
accounts for this difference?
28.
Although the anterior head and face represent only a small
percentage of the body surface, burns to this area are often
more serious than those to the body trunk. Why?
For answers, see Appendix H.
Developmental Aspects
of the Integumentary System
Describe and attempt to explain the causes of changes that
occur in the skin from birth to old age.
Te epidermis develops From the embryonic ectoderm, and
the dermis and hypodermis develop From mesoderm. By the
end oF the Fourth month oF development, the skin is Fairly well
Formed. Te epidermis has all its strata, dermal papillae are ob-
vious, fingerprints have developed, and rudimentary epidermal
derivatives have Formed by downward projections oF cells From
the basal layer. During the fifh and sixth months, the Fetus is
covered with a downy coat oF delicate colorless hairs called the
lanugo coat
(lah-nu
9
go; “wool”). Tis hairy cloak is shed by the
seventh month, and vellus hairs appear.
From Infancy to Adulthood
When a baby is born, its skin is covered with
vernix caseosa
(ver
9
-
niks kă-se-o
9
sah; “varnish oF cheese”), a white, cheesy-looking
substance produced by the sebaceous glands that protects the
Fetus’s skin within the water-filled amnion. Te newborn’s skin
is very thin and ofen has accumulations in the sebaceous glands
on the Forehead and nose that appear as small white spots called
milia
(mil
9
e-ah). Tese normally disappear by the third week
afer birth.
During inFancy and childhood, the skin thickens, and more
subcutaneous Fat is deposited. Although we all have approxi-
mately the same number oF sweat glands, the number that Func-
tion increases in the first two years afer birth and is determined
by climate. ±or this reason, people who grow up in hot climates
have more active sweat glands than those raised in cooler areas
oF the world.
During adolescence, the skin and hair become oilier as seba-
ceous glands are activated, and acne may appear. Acne generally
subsides in early adulthood, and skin reaches its optimal ap-
pearance when we reach our 20s and 30s. Tereafer, the skin
starts to show the effects oF cumulative environmental assaults
(abrasion, wind, sun, chemicals). Scaling and various kinds
oF skin inflammation, or
dermatitis
(der
0
mah-ti
9
tis), become
more common.
Aging Skin
As old age approaches, the rate oF epidermal cell replacement
slows, the skin thins, and its susceptibility to bruises and other
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