Page 196 - Fundamentals of anatomy physiology
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Chapter 5 The Integumentary System 183
epidermis to produce a compound required for calcium ion cold or as a result of cardiovascular or respiratory disorders, such
homeostasis (a process discussed in a later section). However, as heart failure or severe asthma.
UV radiation can also damage DNA, causing mutations and
promoting the development of cancer. Within keratinocytes, Because the skin is easy to observe, changes in the skin’s
melanosomes become concentrated in the region around the appearance can be useful in diagnosing diseases that primar-
nucleus, where the melanin pigments act like a sunshade to ily affect other body systems. Several diseases can produce sec-
provide some UV protection for the DNA in those cells. ondary effects on skin color and pigmentation:
UV radiation can also produce some immediate effects, In jaundice (JAWN-dis), the liver is unable to excrete bile,
such as burns. If severe, sunburns can damage both the epider-
mis and the dermis. Thus, the pigment layers in the epidermis so a yellowish pigment accumulates in body fluids. In ad-
help protect both epidermal and dermal tissues. However, even
though melanocytes respond to UV exposure by increasing their vanced stages, the skin and whites of the eyes turn yellow.
activity, the response is not rapid enough to prevent sunburn
the first day you spend at the beach. Melanin synthesis accel- Some tumors affecting the pituitary gland result in the se-
erates slowly, peaking about 10 days after the initial exposure.
Individuals of any skin color can suffer sun damage to the skin, cretion of large amounts of melanocyte-stimulating hormone 5
but dark-skinned individuals have greater initial protection. (MSH). This hormone causes a darkening of the skin, as if
the individual has an extremely deep bronze tan.
Over time, cumulative UV damage to the skin can harm
fibroblasts, impairing maintenance of the dermis. The result In Addison’s disease, the pituitary gland secretes large quanti-
is premature wrinkling. In addition, skin cancers can develop
from chromosomal damage in basal cells or melanocytes. ties of adrenocorticotropic hormone (ACTH), which is struc-
One of the major consequences of the global depletion of the
ozone layer in Earth’s upper atmosphere is likely to be a sharp turally similar to MSH. The effect of ACTH on skin color is
increase in the rates of skin cancers (such as malignant mela-
noma). In recent years such increased cancer rates have been similar to that of MSH.
reported in Australia, which has already experienced a signif-
icant loss of ozone, as well as in the United States, Canada, In vitiligo (vit-i-LI.-go. ), individuals lose their melanocytes,
and parts of Europe, which have had a more moderate ozone
loss. For this reason, it makes sense to limit your UV exposure causing white patches on otherwise normal skin (Figure 5–5).
through wearing protective clothing and sunscreens during
outdoor activities. The condition develops in about 1 percent of the population.
The Role of Dermal Circulation Its incidence increases among individuals with thyroid gland
Blood contains red blood cells filled with the pigment hemo- disorders, Addison’s disease, or several other disorders. It is
globin, which binds and transports oxygen in the bloodstream.
When bound to oxygen, hemoglobin is bright red, giving cap- suspected that vitiligo develops when the immune defenses
illaries in the dermis a reddish tint that is most apparent in
lightly pigmented individuals. If those vessels are dilated, the malfunction and antibodies attack normal melanocytes. The
red tones become much more pronounced. For example, your
skin becomes flushed and red when your body temperature primary problem with vitiligo is cosmetic, especially for indi-
rises because the superficial blood vessels dilate so that the
skin can act like a radiator and lose heat. p. 37 viduals with darkly pigmented skin.
The skin becomes relatively pale when its blood supply is Figure 5–5 Vitiligo.
temporarily reduced. A light-skinned person who is frightened
may “turn white” due to a sudden drop in blood supply to the Checkpoint
skin. During a sustained reduction in circulatory supply, the oxy-
gen levels in the tissues decline. Under these conditions, hemo- 6. Name the two major pigments in the epidermis.
globin releases oxygen and turns a much darker red. Seen from 7. Why does exposure to sunlight darken skin?
the surface, the skin then takes on a bluish coloration called 8. Why does the skin of a fair-skinned person appear red
cyanosis (sı.-uh-NO. -sis; kyanos, blue). In individuals of any skin
color, cyanosis is easiest to see in areas of very thin skin, such as during exercise in hot weather?
the lips or beneath the nails. It can occur in response to extreme
See the blue Answers tab at the back of the book.
