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Chapter 3
The integumentary system is made up of the skin and the subcutaneous
layer that underlies it. This system makes up most of the external
surface of the body. Because of its position, the integumentary system is
always in direct contact with the external environment and lies between it and
the internal environment of the body. Therefore, this system plays a major
biological role in maintaining a person's homeostasis (i.e., continuing good health) and thus that person's
happy and healthy survival. The major functions of the integumentary system are
serving as a barrier between the body and its surroundings, providing
information about the external environment, regulating body temperature,
starting the process of vitamin D production, and actively defending the body
from harmful physical and biological factors. In addition, because it is a
highly visible system, it frequently affects the social, psychological, and
economic aspects of a person's life.
MAIN FUNCTIONS FOR HOMEOSTASIS
The integumentary system must
provide a barrier against several types of factors because unrestricted entry
or exit of these factors can cause a deviation from homeostasis.
Microorganisms
One
of these factors consists of microorganisms (bacteria and
viruses) that cause infections.
Chemicals
A second factor is chemicals. Many chemicals, such as vitamins, are
within the body because they are needed by the cells. They must not be allowed
to dissipate into the external environment. By contrast, noxious and toxic
substances in the external environment must not be allowed to come into contact
with the body's delicate living cells.
Water Though also a chemical, water
is considered a third factor because it is an especially important substance
and is present in such large quantities. Its movement between the interior of
the body and the external environment must be restricted. The cells of the body
must have enough water to maintain their shape, size, and activities beneficial
to healthy survival because it provides energy needed by the integumentary
system to produce vitamin D. Still, only a small amount of light should be
allowed to penetrate the body because energy from excess light damages several
types of important molecules (e.g., proteins, DNA). The outcome is obvious to
anyone who has had a sunburn.
Light Light is essential for healthy survival
because it provides energy needed by the integumentary system to produce
vitamin D. Still, only a small amount of light should be allowed to penetrate
the body because the energy introduced by excess light damages several of the
most important large molecules, including proteins, RNA and DNA. The outcome is
obvious to anyone who has had a sunburn.
Trauma
The fifth factor to which the integumentary system is a barrier is trauma.
Direct contact of the cells with rough or sharp materials in the external
environment immediately cuts the cells open. The result is the death of those
cells and the portion of the body they constitute. Pressure or sharp blows can
also injure or kill cells.
Gathering information about
conditions in and around the body is essential for survival. It is the first
step in negative feedback systems and positive feedback systems that help maintain homeostasis (i.e., continuing good health).
Since the integumentary system is
between most cells of the body and the external environment, it can supply
information about factors that might alter internal conditions of the body even
before those factors have an opportunity to do so. For example, many abundant
nerve cells in the integument continuously monitor the external environment and
send messages to other parts of the nervous system. As a result, the person
knows much about the area surrounding the body, including the location, size,
shape, texture, movement, and temperature of objects and materials (e.g.,
clothes, furniture, water, air). Then the person can take steps to avoid or
correct any threatening features, perhaps before harm is done. Information
provided by nerve cells in the integumentary system can also provide pleasure
that can improve the quality of life. Examples include enjoyment from physical
touches (e.g., hugs, caresses) and temperatures (e.g., cool breeze, warm
blanket). In later parts of this chapter, other types of cells are mentioned
that monitor conditions to initiate negative feedback or helpful positive
feedback activities contributing to homeostasis.
The maintenance of a proper and
relatively stable temperature within the body is essential not only for comfort
and satisfactory performance but also for sustaining life. The body must be
sufficiently warm that its chemical reactions proceed quickly enough. Cooling
an individual's body can slow chemical reactions so much that the person will
die. In contra too high, certain types of molecules (e.g., proteins) in and
around the cells will be damaged or die. If it is extensive enough, this damage
can result in the death of the individual.
Vitamin D is necessary for healthy survival
because it allows the intestines to absorb calcium from food. The calcium is
then used in many vital ways.
Clearly, the integumentary system
performs a wide variety of necessary jobs. To carry them out, it has many
component structures and materials organized to operate efficiently and
effectively. This chapter will examine the contributions of each of those
components, paying particular attention to those known to change with the
passage of time.
Where possible, changes occurring
because of aging will be distinguished from those caused by environmental
factors or disease. However, these distinctions cannot often be made. For one
thing, the skin is subjected to many environmental influences over long
periods, including sunlight and physical wear. Also, different parts of the
body receive vastly different doses of these influences; perhaps the best
example is differences in exposure to sunlight. Finally, there is tremendous
disparity among the lifestyles of individuals. For example, the skin of a
farmer or a fisher receives very different treatment from that of a person who
works in an office.
Defense
The
integumentary system provides defense when components assist
actively in isolating, destroying or removing a harmful agent from the body
(e.g., splinter, poison ivy sap, bacteria, viruses, cancer cells). Negative
feedback (e.g., healing) and helpful positive feedback (e.g., inflammation,
immune reactions) are used in defense activities. Defense prevents or limits
damage from the harmful agent in the integumentary system and reduces the risk
of damage in other body regions from agents that may spread (e.g., toxins,
infection, cancer).
The epidermis is the
outermost layer of the skin (Fig.
3.1 )
and (Fig.
3.2a ).
It is composed mostly of a thin sheet built up from many layers of flat cells
produced continuously in the deepest region of the epidermis. As they
accumulate, many of these cells are pushed upward toward the outside of the
body. As they move farther away from the favorable internal environment of the
body, they begin to produce a protein called keratin. Therefore,
these cells are called keratinocytes. Finally, these cells are
moved so close to the air that they die, leaving behind their keratin as the
outermost layer of the epidermis, the stratum corneum. Starting
with the formation of a new cell in the deep region of the epidermis, this
process takes about a month.
Keratinocytes produce several
substances that help regulate inflammation and immune responses, which are defense activities. The stratum corneum provides a
barrier against microbes; many chemicals, including water; and abrasion. Though
it is always being gradually worn away at the outer surface, it is maintained
by having new keratin produced at the same rate by the next generation of
keratinocytes. The stratum corneum serves well as long as it remains thick
enough and is not broken by cuts, tears, scrapes, or burns.
If the keratin is injured, the
keratinocytes reproduce at a faster rate and repair the damage, as occurs when
a cut heals. The epidermis can even form a thick pad of keratin a callus) in areas that are
regularly subjected to physical abuse. Thus, the keratinocytes provide
adaptation to maintain homeostasis.
The keratinocytes are aided by other
types of cells. One type is in the innermost layer of the epidermis and
produces the brown skin pigment melanin. Cells of this type are
called melanocytes (Fig.
3.2a )They
make up 2 to 3 percent of the cells in the epidermis.
Melanocytes send melanin into
keratinocytes that are about to begin migrating toward the outer surface of the
skin (Fig.
3.2b ).
The melanin helps maintain homeostasis (i.e., continuing good health)
by absorbing excess light. Recall that
excess light can cause great harm to the body. This is especially true of
ultraviolet (UV) light, which contains a great deal of energy and is
particularly well absorbed by proteins, RNA, and DNA. UV light is in high
concentration in sunlight and in the light from certain bulbs, such as those
used for getting a tan.
Excess light is hazardous to the
body because it changes the structure of molecules. There are three main
undesirable outcomes. One is damage to the protein molecules making up much of
the inner layer on the skin (i.e., dermis), which are discussed later in this
chapter. This damage may contribute to wrinkling of the skin. The second
outcome is injury to the protein molecules inside the cells. The result can be
painful and severe sunburn with blistering and peeling of the epidermis.
Besides causing pain, such injury detracts from the barrier functions provided
by the keratin. The third outcome is alteration of DNA, which can lead to skin
cancer.
Fortunately, enough melanin can usually
be produced to significantly reduce the incidence of these problems. Like the
keratinocytes, the melanocytes are adaptable, and they increase their
production of melanin when the skin is exposed to excess light. This is evident
as the development of a tan. Melanocytes also decrease melanin production when
less light is encountered. Then, as the melanin‑rich keratinocytes die
and are sloughed off at the surface of the skin, melanin‑poor
keratinocytes replace them and the tan fades.
Immune
Function and Langerhans Cells
The third type of important cell in
the epidermis is one that starts a body defense strategy called an immune
response (Chap. 15). These cells are called Langerhans cells
(dendritic cells) and make up less than 1 percent of the epidermal cells (Fig.
3.2a and
Fig.
3.2c ).
Their specific function is to monitor substances throughout the epidermis to
determine whether they are native to the body or foreign. These substances may
be free molecules between the cells, molecules on the surfaces of microbes, or
viruses. Of course, being near the surface of the body, Langerhans cells are
positioned to guard against the entry of harmful materials and organisms.
When a Langerhans cell determines
that a substance is foreign and therefore does not belong in the body, it
alters that substance so that other cells in the immune system can attack and
eliminate it. This helps maintain proper chemical conditions within the body
and greatly reduces the risk of infection and cancer.
Thickness The
overall thickness of the epidermis changes little with advancing age, though
the epidermis becomes slightly uneven in different parts of the body. Of
greatest importance is the fact that the stratum corneum in protected areas,
such as those usually covered by clothing, becomes only slightly thinner.
Therefore, the keratin retains most of its ability to serve as a barrier
against microbes and viruses, water, and abrasion. However, the slight thinning
allows certain substances to penetrate the epidermis more easily. Therefore,
the elderly should be careful about skin contact with chemicals and topically
applied medications.
Structure Two other microscopic changes in the
epidermis have been observed. One is the increase in variability of the size,
shape, and internal structure of keratinocytes in the deeper regions. These
irregularities may indicate initial abnormalities in cells that are precursors
to skin cancer. Skin cancers are among the most common types of cancer in the
elderly.
The second structural change is a
decrease in the strength of attachment and an increase in the spacing between
cells and between keratin materials. These changes may be an additional reason
for the increased chemical permeability of the epidermis. The separation of the
scaly bits of keratin, with their flattening and broadening, also contributes
to the age‑related increase in the scaliness of the skin.
Replacement
There is an age-related decrease in the secretion of some signaling
substances by keratinocytes. The rate of new keratinocyte production also
decreases. The amount of decline is different in different individuals, and the
rate of decline becomes much faster after age 50. By age 75, the rate of cell
production may drop to 50 percent of the rate in youth. These changes cause a
decrease in the speed of wound healing, leading to an increase in the risk of
infection.
Aging affects the melanocytes also.
The somewhat uneven distribution found in youth becomes much more pronounced because
while the total number of melanocytes decreases, certain areas of the skin
develop clumps of melanocytes. These clumps form dark "age spots" or
"liver spots" that are noticeable against the gradually fading
coloration of the rest of the skin. By contrast, the number of dark moles
decreases because of the overall reduction in melanocytes. Still, the result is
that the elderly have a paler but increasingly mottled
skin coloration.
The widespread reduction in the
number of melanocytes due to their shorter lifespans and slower production,
combined with a cessation of melanin production in increasing proportions of
the remaining melanocytes, causes a decline in protection from excess light.
Therefore, elderly people who are exposed to sunlight cannot develop as dark a
tan as they did when they were younger. It also takes them longer to develop a
tan. This places the elderly at much higher risk of suffering sunburn and skin
cancer from exposure to sunlight.
Immune
Function and Langerhans Cells
Langerhans cells decrease
dramatically with aging. By the time of very old age, the number of these cells
declines to less than half the number present in youth. The reduction is
greatest in areas of the skin chronically exposed to sunlight. Because of
declining numbers of Langerhans cells, one of the body's first lines of defense
is largely crippled. This leaves the elderly with more inn cancers that would
otherwise be eliminated by the immune system. It also decreases allergic
reactions by the skin. This change may seem beneficial since such reactions can
be uncomfortable, but allergic reactions serve as a warning sign that the body
has come into contact with a harmful agent (e.g., noxious chemicals). Without
this warning sign, steps to avoid or correct problems are not taken, and this
may place a person in jeopardy from these agents.
EPIDERMAL ACCESSORY STRUCTURES
There are many places in the skin
where groups of epidermal cells have sunk into the underlying dermis so that
they may form additional helpful structures. Two of these structures are hair
and nails, which will be discussed here because they are visible on the surface
of the skin. The others (i.e., sweat glands, sebaceous glands) will be
discussed as part of the dermis because they are under the epidermis proper.
Recall that the upper layer of the
epidermis consists of a thin layer of keratin. Hair is also made of keratin.
Each hair is formed at the bottom of a deep pit of epidermal cells called a hair
follicle, which extends down into the dermis (Fig.
3.1
(Fig. 3.1 ). At the base of the follicle, the same processes that
produce the stratum corneum occur, leaving the keratin behind as the shaft of
the hair.
Each follicle is not always making
hair. On a fairly regular basis, the production of cells in a follicle slows
and may even stop. When this occurs, the hair falls out and the follicle enters
a resting period. After a while the follicle will begin producing cells and melanin
again, and a new hair will emerge.
Hair is found on almost all parts of
the skin. In areas such as the forehead, it is sparse, thin, and light in color
and has only a slight value. However, the scalp, eyebrows, and eyelids have
dense, thick, and long hairs that contribute substantially to a person's well‑being
in a variety of ways.
Perhaps the most obvious is its
cosmetic value. To appreciate this, one need only notice how much time, energy,
attention, and money people spend on their hair. A person's appearance has
great social, psychological, and economic impact on the quality of his or her
life; this holds true for the elderly as well as the young.
Hair also has several biological
functions. For example, scalp hair shades the head from sunlight, provides a
thermal insulating layer, and cushions the head against bumps. The hair around
the eyes shades them and filters out dust and other small particles. The hair
in the openings to the nose and ears also serves as a filter.
In addition, hair helps increase the
skin's sensitivity to touch. Since hairs jut out from the surface of the body,
any object or material that is about to touch the skin or is moving along its
surface collides with these hairs. When such collisions move a hair, its motion
travels down the shaft to nerve endings around the follicle. These nerve
endings detect the motion and send impulses to the brain, informing the person
of the presence and motion of the object or material. Recall that such
monitoring is the first step in the negative feedback processes necessary for
healthy survival. The person can then take the necessary steps to avoid or
remove the object or material. Alternatively, if the object or material causing
the motion is not harmful, the person may derive pleasure from the sensations,
such as those from a caress or a gentle breeze.
Aging results in four changes that decrease
the amount of visible hair. First, there is a decrease in the number of
follicles, which decreases the total number of hairs present. Second,
increasing proportions of the remaining follicles spend longer periods in the
resting stage. This further reduces the amount of hair, since follicles have no
hair present during the resting stage. Third, when follicles reenter the active
stage, they produce hair more slowly, and so it takes more time for a new hair
to emerge. Fourth, almost all the hairs produced are thinner‑related
decreases in the levels of sex hormones are the main reason for the decline in
armpit and pubic hair. However, relatively high levels of male sex hormones
(e.g., testosterone) cause more rapid loss of hair from the scalp. Since aging
men retain relatively high levels of sex hormones, they lose much scalp hair.
Furthermore, men who have inherited the genes for pattern baldness lose
increasing amounts of hair from the crown of the head. Women also have some
male sex hormone, which is produced by the adrenal gland. Since the level of
male sex hormone in women is low before menopause, loss of scalp hair in women
is low at first. After menopause, this loss increases dramatically because
menopause is accompanied by a rise in male sex hormone.
While a decrease in both the amount
and thickness of hair occurs in most areas of the body, some exceptions occur.
In aging women these include an increase in facial hair and thickening and
lengthening of some hairs on the chin and upper lip. In aging men, thicker and
longer hairs are produced in the eyebrows, on the external ears, and within the
ear canals and nostrils. All these alterations can be cosmetically troublesome.
Other cosmetically important changes
include the development of air pockets within hairs and decreases in the amount
of oil secreted onto the hair, resulting in a loss of softness and luster. In
addition, the number of melanocytes in each follicle declines, resulting in a
decline in the intensity of hair color. As more follicles lose all their
melanocytes, increasing numbers of hairs become white. With declining pigment
in each hair and fewer hairs containing any pigment, the hue of a person's hair
becomes gray and finally white.
The time and rate of graying are
determined mostly by genes. Both the time of onset and the rate of graying of
scalp hair are not well correlated with chronological age, and graying of scalp
hair shows wide variation among individuals. Therefore, gray hair is a very
poor indicator of chronological age. By contrast, the initiation and progress
of graying of axillary hair are very good indicators.
The consequences of age changes in
hair vary. The amount of cushioning provided for the head remains high. Shading
of the eyes, and the filtering action and the contributions to touch sensation
hair provides, may improve when hairs thicken and lengthen. By contrast, the
decline in the abundance of hair results in decrements in shading and thermal
insulation for the scalp. However, wearing a hat can provide the same type of
protection for the scalp.
Because of decreases in both the
number and length of hairs in most areas, there are widespread reductions in
the contributions hair makes to touch perception. This
reduction is exacerbated by the decline in both the number and functioning of
sensory nerve cells.
All these biological effects may
seem slight compared with the variety and degree of social, psychological, and
economic effects caused by the appearance of becoming old. While there may be
some positive effects from appearing to be older or more mature, most of the
effects are negative.
Like hair, fingernails and toenails
are made of keratin produced by essentially the same process as is the keratin
in the stratum corneum and in hair. However, no melanin is incorporated into
nails.
Nails serve primarily to protect the
fingers and toes from traumatic injuries such as crushing, cuts, and scrapes.
They can also be used like tools to pick up small objects or scratch irritants
off the skin. In addition, though the toenails are usually hidden from view,
the fingernails are usually very visible and therefore can have a significant impact
on a person's appearance.
As a person ages, the rate of growth
of nails decreases by as much as 50 percent and the thickness and strength of
the nails also decrease. The keratin plate becomes less clear, longitudinal
grooves develop, and the growth zone at the base of the nail decreases in size.
Though these changes are primarily due to aging, they can also be caused by
trauma and reduced blood flow to the extremities. Changes are greater in the
toenails than in the fingernails because there is a greater age‑related
decline in the blood supply to the feet compared with the hands.
Age changes in nails have several
undesirable consequences. The structural weakening of the nails makes them
susceptible to injury and disfigurement. The declining growth rate means that
the damage is present for a longer period before the injured part grows out and
is worn off or cut away. Therefore, nails are less able to perform their
functions. Furthermore, because of the higher incidence, severity, and duration
of nail injuries, fungal infections of the nails become more common.
Such infections cause the nails to
thicken, become opaque, and become misshapen. Infected nails may become
unsightly, causing cosmetic problems. In addition, curing fungal nail
infections takes longer because a declining blood supply to the nails causes
medications to be delivered more slowly. Eventually fungal infections of the
toenails may become impossible to cure.
Aging and disease changes in the
toenails can have a more serious biological impact than can those in the
fingernails because the toenails are out of sight most of the time and
therefore often do not get proper care. Furthermore, because of age changes in the
eyes and the skeletal system, it is increasingly difficult for aging
individuals to see and reach their toenails, resulting in further decrements in
toenail care. For example, toenails may become so large that they interfere
with the proper fit of shoes, making walking difficult or painful. Toenails are
also common sites of infection in diabetics.
The skin layer under the epidermis
is called the dermis (Fig.
3.1 ).
It is considerably thicker than the epidermis and contains many different types
of structures, include vessels, nerve cells, and small muscles. These
structures are embedded in a foundation material consisting mostly of fibers
and some cells suspended in a small quantity of soft gel. The gel consists
mostly of water with some complex proteins and carbohydrates. Because of the
variety of its structures, the dermis makes many contributions to three of the
four main functions of the skin discussed earlier in this chapter.
Fibers
Fibers made of protein are the most abundant
material in the dermis. The protein fibers are mainly of two types. Collagen fibers
constitute approximately 80 percent of the fiber materials, and the others
consist of elastin fibers.
The collagen fibers are tangled with
each other to form a dense mat. This ensures that the skin will not split open
or tear when it is subjected to pulling or twisting forces or is cut.
Therefore, it is like a rip‑stop fabric. Still, the mat is very flexible
so that parts of the body can bend freely.
Elastin fibers are mixed among the
collagen fibers. Because of their elasticity, these fibers cause the skin
automatically to return to its original position after it has been pulled,
bent, or twisted out of shape.
Cells Scattered among the dermal fibers are cells
of various types. The most abundant type, accounting for about 60 percent of
these cells, is the fibroblast. Fibroblasts produce and secrete
the proteins that form collagen and elastin fibers. They are regulated by
chemical and physical signals. Sunlight inhibits collagen production.
Macrophages ("large eaters")
constitute 20 to 40 percent of the dermal cells. They wander about among the
fibers, engulfing and digesting unwanted materials, including cellular debris,
foreign substances, and bacteria. Macrophages are also important as defense
cells because they function like the Langerhans cells of the epidermis.
Additional defense cells in the
fibers include white blood cells that attack and remove harmful materials in a
variety of ways (see Chaps. 4 and 15). Mast cells release a substance called histamine.
Whenever there is injury to the dermis. Histamine starts the process of inflammation
(Fig.
33. )
(Erythrocytes
are red blood cells (RBCs), leucocytes are white blood cells (WBCs), and
thrombocytes are platelets.)
Inflammation in any part of the body
involves an increase in the diameter of blood vessels and in the porosity of
the smallest vessels (capillaries). These changes deliver more white blood
cells to the injured area to protect the body from infection and remove damaged
body cells. More oxygen and nutrients are also brought to the area to supply
body cells with all the materials they need to repair the injury. The extra
fluids that arrive cause swelling and usually help flush away toxins and
debris. In more serious vessel damage, movement of the fluid is inhibited by
clotting materials that leak out of the vessels. The redness, swelling, and
pain that accompany inflammation serve as warning signs that an injury has
occurred. In addition, the pain encourages the person to avoid the
circumstances that caused the injury and limit the use of the damaged area
until healing has occurred.
Beyond their role in defense, mast
cells release a substance called heparin, which stimulates the
migration of cells that form new blood vessels in the dermis. These new vessels
are important when new dermal components are formed during the healing of a wound
and when the skin grows.
Gel As was mentioned above, the fibers and cells
of the dermis are surrounded by a small amount of soft gel material. This gel
is made up mostly of water but also contains a variety of large and small
molecules dissolved in the water. The water provides a favorable environment
for the cells, allows materials to get to and from the cells, and maintains the
firmness of the skin. The large molecules provide firmness by keeping enough
water in the dermis. They also bind together the other structures in the dermis
as a soft glue would. Most of the small dissolved molecules are either
nutrients moving to the cells or waste products moving to the blood vessels for
removal from the skin. Some inactive vitamin D is also in the water. The
vitamin D moves out of the dermis after being acted upon by light (see Vitamin
D, below).
Age Changes in Fibers and Cells
The collagen fibers of the dermis undergo substantial changes with
increasing age. These changes have a profound effect on the properties of the
dermis and the ability of the skin to perform normally. One change is a gradual
decrease in the amount of collagen. The remaining collagen fibers become
thicker and less organized and form larger bundles of fibers. These changes may
be due to the increase in the number of cross‑links between the fibers.
The increasing cross‑links make the fibers stiffer and less able to move,
leaving the skin stiffer and less able to stretch. Pulling forces are then more
likely to cause injury to the skin because the skin yields less when pulled.
The progressive cross‑linking
of collagen does not continue throughout life, however. In very old age enzymes
in the skin break down the cross‑links faster than they can form. Then
the strength of the collagen mat decreases, and the skin can be torn more
easily.
Age changes in elastin fibers are
not as well documented, partly because of the difficulty of distinguishing age
changes from changes caused by exposure to sunlight. In any event, elastin
fibers become thicker, stiffer, more tightly bound by cross‑links, less
regular in their arrangement, and, sometimes, impregnated with calcium. The
changes in dermal elastin fibers are virtually identical to the changes that
occur in the elastic fibers in arteries altered by atherosclerosis (Chap. 4).
While changes in elastin fibers do
not alter the ability of the skin to be stretched, they reduce its tendency to
return to its original shape and size after being pulled. The skin also does
not regain its normal thickness as well after being compressed. Overall, then,
the skin seems to become a looser covering that hangs
from the body.
With advancing age, the number of
fibroblasts increases. This increase may result from an accumulation of old
cells and a decrease in the ability to produce new ones. The old fibroblasts
may also have less ability to produce new fibers to replace older fibers.
Therefore, age changes in the fibroblasts may permit the accumulation of age
changes in the fibers and the resulting alterations in the properties of the
skin. Furthermore, the deterioration of fibroblasts seems to contribute to the
gradual reduction in the speed and strength of skin healing.
Unlike the fibroblasts, the numbers
of dermal macrophages and white blood cells seem to decrease with age. The
result is a reduction in the defense functions performed by the skin, including
a lowered ability to prevent infection, remove harmful chemicals and debris,
and initiate immune responses. Therefore, the healthy survival of the entire
body is at greater risk.
The age‑related decline in the
number of dermal mast cells, which may reach 50 percent, also reduces the
defense function of the skin. With fewer mast cells, there is a lowering of
both the speed and the intensity of inflammatory responses. Therefore, there is
both less warning that injury is occurring and reduced defense against further
damage. Furthermore, the declining population of mast cells cannot produce as
much heparin. This results in a declining ability to produce new blood vessels
in areas of healing and may be a main factor contributing to the normal
decrease in the number of dermal blood vessels.
Another age change in the dermal
foundation material involves large molecules called mucopolysaccharides, which
hold much water. The amount of mucopolysaccharide in the dermis decreases
slightly. Therefore, the amount of bound water also declines, and so the firm
consistency of the skin diminishes. The skin becomes more easily compressed and
returns to its original thickness more slowly. The decrease in bound water may
also reduce the movement of small molecules through the dermis. This means that
skin cells are not as well serviced. Finally, the reduction in the amount of
water held in the dermis probably contributes to the general thinning of the
dermis and the thinner appearance any elderly people.
The blood vessels in the dermis are
numerous, although some areas of the body (e.g., scalp) have more of them. Like
all vessels that carry blood, the dermal vessels deliver useful materials to
the cells and carry away manufactured substances that can be used elsewhere in
the body. These vessels also remove wastes produced by the cells. Furthermore,
blood flow in these vessels delivers white blood cells and antibodies for
defense of the area they serve.
Dermal vessels also help regulate
body temperature. They widen when the temperature in the body rises above the
desirable level. This widening is called dilation (or vasodilation),
and it allows more warm blood to flow close to the surface of the body. Much of
the heat in the blood passes out of the body to the cooler surrounding
environment. The result is a lowering of the body temperature so that it is
again in the desirable range.
Conversely, if body temperature
drops below the normal level, the dermal vessels become narrower. This is
called constriction (or vasoconstriction),
and it reduces blood flow through the vessels. With less warm blood flowing
near the surface of the body, the rate of heat loss is reduced. The body can
then become warmer as its muscles and other active cells produce more heat.
Age Changes in Dermal Vessels
With aging, the number of dermal blood vessels decreases substantially,
particularly in the layer just below the epidermis and in skin chronically
exposed to sunlight. The remaining vessels often show irregularities in
structure. These changes cause a decrease in blood flow to the dermis.
This reduction in blood flow
decreases the delivery of nutrients to all dermal structures. This may be a
main reason for the age‑related shrinkage and decline in function of many
skin structures. There is also slower removal of material (e.g., wastes, vitamin
D), and the delivery of white blood cells and antibodies declines. Even the
epidermis, which has no vessels of its own and therefore depends on blood flow
in the dermis, is serviced less well. Reduced blood flow can also cause
paleness of the skin. Furthermore, reduced dermal blood flow can be of great
importance for elderly individuals who use topically applied medications, which
can reach dangerously high concentrations in the skin. Meanwhile, the rest of
the body, which may need the medication, receives less because the medication
remains in the skin.
Adding to the problems caused by
reduced dermal blood flow is the increase in thickness of a layer of material
that surrounds the capillaries. This layer, the basement membrane, is
normally quite thin. It allows certain white blood cells and many substances to
enter and leave the capillaries freely so that the areas near the capillaries
are well serviced.
The age‑related thickening of
the basement membrane inhibits the movement of white blood of the circulatory
system to provide for the needs of the skin.
The aging of dermal vessels also
adversely affects the thermoregulatory function of the skin. As blood flow
declines, there is a reduction in the ability to release excess heat from the
body. The vessels also constrict and dilate more slowly and to a lesser degree.
The result is a reduced ability not only to release heat but to slow heat loss
when the body begins to get chilled. These changes constitute a major reason
the elderly have difficulty maintaining normal body temperature when the
external temperature deviates from a moderate level or when activities such as
vigorous exercise cause an alteration in body temperature.
The dermis contains two types of
sweat glands. Eccrine sweat glands secrete a watery material that
is the visible perspiration (i.e., sweat) seen when a person becomes
uncomfortably warm. The other type of sweat gland is the apocrine sweat
gland.
Each eccrine sweat gland is a
tubular gland with a highly coiled portion, in the dermis, which produces most
of the perspiration (Fig.
3.1 ).
The coiled portion leads into a fairly straight portion that extends upward
through the dermis and epidermis and finally opens onto the surface of the
skin.
The purpose of the perspiration
produced by these glands is to cool the body. When the brain detects an
abnormal rise in body temperature, it sends nerve impulses to the glands,
stimulating them to secrete perspiration. The water in the perspiration
evaporates when it reaches the surface of the skin. As it evaporates, it
carries heat away from the skin, resulting in a lowering of body temperature.
Perspiration also contains a number
of substances, including useful ones such as salt, which are dissolved in the
water. However, the secretion of these useful substances is not beneficial to
the body. Serious problems such as muscle cramps and dizziness can develop if a
person perspires abundantly without replacing the useful substances by drinking
beverages or eating foods that contain more of these substances.
Unlike the eccrine sweat glands,
which are widespread, most apocrine sweat glands are in the skin of the armpits
and in the genital area. These glands secrete a small amount
of thick materials that do little to promote healthy survival. This secretion
is a main source of unpleasant body odor.
Apocrine gland activity is
controlled largely by the level of sex hormones in the body, though the nervous
system may increase the secretion during periods of stress or intense emotions.
Age Changes in Sweat Glands With aging, the number of eccrine sweat
glands decreases dramatically in all parts of the body except the scalp. The
remaining glands are reduced in size and produce perspiration at a decreasing
rate.
The result of these changes is a
reduction in the ability of the glands to cool the body. This puts the elderly
at an ever increasing risk of becoming overheated in
particularly warm environments or during vigorous exercise.
Though changes in the number of
apocrine sweat glands have not been well studied, it is known that they shrink
and that their rate of secretion diminishes significantly. This is probably due
to age‑related reductions in sex hormone levels. This is one of the few
alterations with advancing age that most people agree is desirable since
diminishing apocrine gland secretion leads to a substantial decrease in
unpleasant body odor. While apparently having no biological importance, this
change can have positive effects on other parameters (e.g., social).
Besides sweat glands, the dermis
contains glands that produce an oily substance called sebum;
these glands are called sebaceous glands (Fig.
3.1 ).
Sebaceous glands are usually found beside hair follicles and secrete sebum into
the follicles. The sebum coats the hair, and as it leaves the follicles, it
spreads out to form a thin coating on the epidermis.
Sebum contributes to the maintenance
of homeostasis mainly by removing the ability of the skin to act as a barrier.
Because sebum is an oily material, it helps make the keratin of the epidermis
more impermeable to water. It also helps keep the keratin pliable so that the
stratum corneum does not crack when it is bent. Cracks in the keratin could
allow water and other chemicals to leak into and out of the body and permit the
entrance of harmful microbes. In addition, certain materials in the sebum
inhibit the growth of fungi that could break down keratin.
Sebum is also cosmetically important
because it gives skin keratin a smoother appearance and adds luster to the
hair. Finally, by keeping keratin pliable, sebum reduces the breaking and
splitting of hair.
Age Changes in Sebaceous Glands
Though there seems to be no age change in the number of sebaceous glands
and though they increase in size, there is a decrease in the production of
sebum. This decline seems to result from declining levels of the sex hormones
that normally stimulate sebum production.
The reduction in sebum production
lowers its contributions, though the amount produced is usually sufficient to
prevent serious biological problems. However, the cosmetic contributions made
by sebum decline substantially. The results are the clearly visible signs of
aging of the skin and hair. The widespread use of skin and hair lotions that
augment the diminished contributions of sebum attests to the importance of
these cosmetic changes.
The two types of nerve cells (neurons)
are sensory neurons and motor neurons (Fig.
3.1 ).
Sensory neurons monitor conditions in and around the dermis, including
conditions in the epidermis and the external environment. Sensory neurons send
information about these conditions to the brain and spinal cord. Motor neurons
control the functioning of blood vessels and eccrine sweat glands by relaying
instructions from the brain and spinal cord to the skin.
Sensory Neurons
There are several types of sensory neurons in the dermis, each of which
is specialized to monitor a single kind of stimulus (e.g., light touch, heat,
pressure). An additional type is activated when conditions vary greatly from
normal or there is injury to the skin. This type of sensory neuron warns of the
danger by providing the sensation of pain.
Beyond determining if there has been
a change in conditions near the surface of the body, sensory neurons provide
information about what type of change has occurred and the location of that
change. The nervous system can then initiate the proper type of response to
preserve the well‑being of the body.
Motor Neurons Information about the structure and function of
the motor neurons of the skin and the effects of aging on these neurons is
presented in Chap. 6.
Age Changes in Sensory Neurons As a person ages, there is little
change in the number or structure of the sensory neurons for pain and the touch
receptors connected to hair follicles. Conversely, the numbers of touch
receptors not connected to hair follicles and of pressure receptors decrease
dramatically. In addition, there are alterations and distortions in the
structure of both types of receptors. Little is known about the effects of
aging on the other types of sensory neurons.
As a result of age changes in
sensory neurons, there is decreased sensitivity to touch, pressure, and
vibration. This is especially evident in the fingers, the palms of the hands,
and other areas of the body lacking hair (e.g., the penis). In addition, there
is a decreased ability to detect the exact location of touch and pressure
stimuli and therefore to determine the shapes of objects by touching them. One
practical consequence is a reduction in manual dexterity. Interestingly, the
thinning of the skin with age compensates somewhat for changes in sensory
neurons allowing stimuli to reach these neurons more easily.
These sensory decrements reduce the
ability of the skin to inform the body about conditions on and just outside its
surface. The person is then less able to respond negatively to dangerous or
harmful stimuli and positively to helpful or pleasurable stimuli.
The ability of the skin to perform
its monitoring function is adversely affected by many factors beyond changes in
the number and shape of its sensory neurons. Some of these factors include the
consistency of the skin and the subcutaneous layer; the ability of the neurons
to conduct impulses to the brain and spinal cord; and the ability of the brain
and spinal cord to process and interpret those impulses (Chap. 6).
BOUNDARY BETWEEN EPIDERMIS AND DERMIS
The boundary between the epidermis
and the dermis is important for the maintenance of the structure and
functioning of the skin. For example, it is the region through which nutrients
pass upward to the epidermis and wastes pass downward to the dermis. This
exchange is essential for the epidermis, which has no blood vessels to service
its cells. Keratinocytes in the epidermis have special projections that attach
to the dermis to help in this exchange, which is also helped by many blunt
projections from the dermis that extend up into the epidermis. These
projections, called dermal papillae, increase the rate of
exchange of materials by increasing the contact (i.e., surface area) between
the two layers. The dermal papillae also contain special tufts of capillaries
that further increase the ability of the dermis to service the epidermis (Fig.
3.1 ).
besides improving the exchange of
materials, the boundary between the epidermis and the dermis provides a strong
attachment between the layers. The keratinocyte projections help by gripping
the dermis, and the dermal papillae also help in this regard. As a result, the
boundary can prevent separation of the epidermis from the dermis when sliding
or pulling forces are applied to the surface of the skin.
The dermal papillae are usually
scattered about in most areas of the skin. However, they are in very regular
rows in the skin on the front of the hands and the bottom of the feet. These
rows produce the ridges known as fingerprints, which make the skin less
slippery and improve a person's ability to grip objects.
Age
Changes in the Epidermal‑Dermal Boundary
As
a person ages, the projections from the keratinocytes decrease in number and
both the number and length of the dermal papillae decrease. The distribution of
small vessels in the papillae becomes uneven. The result is a reduction in the
functions of the boundary. First, there is less exchange of materials b dermis.
Therefore, the epidermis is weakened, is injured more easily, and heals more
slowly. Second, the weakening of the connection between the epidermis and
dermis leads to easier blister formation in the elderly when the skin is
subjected to physical forces. Such forces are encountered when one performs
ordinary activities such as sweeping and gardening. They are also present when
the skin is pulled, as occurs during the removal of adhesive bandages. The
resulting injuries not only are painful but also increase the risk of skin
infection. Finally, as the fingerprints become less prominent, keeping a firm
grip on objects is more difficult.
Though the production of vitamin D begins
in both the epidermis and the dermis, most of it occurs in the epidermis. Skin
cells start the process by modifying cholesterol molecules. When the modified
molecules are struck by light, they are altered again to form an inactive form
of vitamin D. Ultraviolet light seems to be the best type of light for this
process, and sunlight is the natural source of UV light for the body. Exposure
of the hands and face to only 10 to 15 minutes of summertime sunlight provides
enough light for the skin to produce all the vitamin D needed by the body.
Inactive vitamin D is carried away by the blood in dermal blood vessels.
The inactive form of vitamin D can
also be obtained from foods such as fish and vitamin D-enriched milk. Whether
from the skin or from the diet, inactive vitamin D is sent to other parts of
the body (i.e., liver and kidneys) for additional modification and final
activation. It is then transported throughout the body. Vitamin D influences
movement of calcium into and out of bones directly and indirectly. Vitamin D
reaching the intestines helps absorb calcium from food.
Calcium performs many essential
functions in the body. It is a main building material in bones and teeth and is
essential for the contraction of muscles, the passage of impulses in the
nervous system, and the clotting of blood. Calcium also controls many chemical
reactions in cells.
Age
Changes in Vitamin D Production
The ability of the skin to produce inactive
vitamin D decreases with age. This seems to result from several factors. For
example, there may be a decrease in the delivery of cholesterol‑like
molecules to the skin because of the decrease in blood flow in the skin. Also,
the skin cells seem slower at converting this material. Furthermore, the
process powered by light becomes less efficient. Therefore, an older person
must get more exposure to sunlight to produce the same amount of vitamin D.
Finally, the slower movement of materials through the skin and the decrease in
dermal blood flow may slow the removal of inactive vitamin D from the skin.
The overall result of reduced
vitamin D production by the skin is an increased risk of vitamin D deficiency
with age. The risk is further increased because the elderly often have less exposure to sunlight because of reduced mobility,
social customs, and the higher risk of developing sunburn. There is also a
decline in the ability of the kidney to complete vitamin D activation. If a
vitamin D deficiency develops, the absorption of calcium will become
inadequate. All body functions that depend on calcium will then become
abnormal.
Fortunately, many ordinary foods
(e.g., bread, milk) have vitamin D added to them. Incorporating such foods into
the diet can largely eliminate the risk of vitamin D deficiency. In situations
where the diet cannot provide the necessary vitamin D, vitamin supplements such
as vitamin pills can do so.
The subcutaneous layer
lies under the dermis ((Fig.
3.1 ).
While this layer is usually not considered part of the skin, it makes up the
innermost layer of the integumentary system.
The foundation material of the
subcutaneous layer is made of loose connective tissue that contains a soft gel
consisting of a large amount of water with some protein and other substances
dissolved in it. Within the gel are various types of cells and widely scattered
collagen and elastin fibers.
The soft gel serves as a cushion
under the skin. It is slippery and therefore allows the skin to slide easily
over the underlying muscles and bones. As in the dermis, some cells produce the
gel and fibers, while others defend the body against microbes and harmful
chemicals. The fibers hold the other components in place and attach the skin to
the body. Since these fibers are relatively low in number, they allow the skin
to move easily, though only a limited distance over the underlying structures.
Fat tissue is also found within the
subcutaneous layer. Some areas of the body (e.g., buttocks) have a thick layer
of fat, while other areas (e.g., hands) have a thinner layer. There is also a
wide degree of difference among individuals in terms of fat in the subcutaneous
layer.
Fat tissue is a very important
component of the subcutaneous layer. First, the soft but somewhat firm
consistency of fat allows it to cushion the inner body parts, protecting them
from injury by pressure and forceful blows. Second, because of its firmness,
fat helps maintain the contour of the skin. Thus, in moderate amounts and when
distributed well, fat contributes to a pleasing appearance. Third, since fat is
a thermal insulator, it helps maintain proper body temperature by reducing the
rate of heat loss through the skin. Finally, fat is a nutrient storage
material. If the diet does not provide enough energy or building materials for
the body, the cells break down fat molecules. Body cells can obtain a great
deal of energy and raw materials in this way.
Age
Changes in the Subcutaneous Layer
There is little information about
the effects of aging on the loose connective tissue of the subcutaneous layer.
There is a general decrease in the amount of subcutaneous fat tissue with
aging, but there is little decrease in the total amount of fat in the body. The
explanation is that while the amount of subcutaneous fat is decreasing, the
amount of fat increases in the inner regions of the body, such as around the
organs inside the abdomen. One effect of the generalized thinning of
subcutaneous fat is a decrease in the ability of an older person to stay warm
in a cold environment. Another effect is a reduction in the support of the
skin. This, with changes in the dermis, makes the skin appear loose. The skin
may even seem to hang in folds on the face and other parts of the body. The
thinning of the fat may also contribute to the more translucent appearance of
the skin of elderly individuals.
Changes in the proportion of fat in
different areas of the body also seem to be very important. This is currently a
topic of considerable research, but only a few conclusions can be drawn. For
example, the substantial decrease in fat on the bottom of the feet reduces
their ability to cushion the body. It also seems that the distribution of body
fat is related to the incidence of certain diseases (e.g., coronary artery
disease, diabetes).
Though the immediate biological
effects of an altered distribution of subcutaneous fat on healthy survival are
uncertain, the cosmetic effects are very apparent. The subcutaneous fat of the
arms and legs thins, as do the muscles in those areas. At the same time, there
is a thickening e trunk of the body. The result is a dramatic change in body
proportions, with the waist seeming to get much larger with age. This change
occurs to a greater degree in women than in men. Weakening of the abdominal
muscles and other muscles important in maintaining good posture can exaggerate
the result.
These changes in subcutaneous fat
are believed to occur in most people because of aging. However, there is an
enormous degree of variability among individuals because many factors besides
aging can affect fat tissue. For example, alterations in diet, exercise, and
hormone levels can profoundly change the amount and distribution of fat.
Therefore, as individuals get older, a considerable change in their appearance
may alter their social interactions, psychological health, and economic status.
MISCELLANEOUS COSMETIC CHANGES
Three additional cosmetic changes in
the integumentary system will be mentioned here because they are often
associated with aging. One is the gradual increase in the width of the nose and
size of the ears. Most of the perceived lengthening of the nose is due to
age-related changes in the skin and shrinkage of muscle and bone near the nose.
A second cosmetic change is wrinkling of the skin. Wrinkling has been
attributed to changes in the fibers in the dermis, changes in the foundation
material in the dermis, fat loss from the subcutaneous layer, and the pull of
muscles on the skin. All these factors may contribute somewhat to wrinkling,
but none has been shown to be the fundamental cause. The third change is drying
of the skin. Changes in keratin and reductions in the production of sweat and
sebum may enhance the dry appearance of the skin, but the actual cause of skin
dryness has not been identified. (Suggestion:
Chap 03 - 63-1-4)
The ability of the integumentary
system to serve the body is reduced by factors other than aging. While all
these factors can affect the integument in the young as well as the elderly,
they are more relevant for the elderly. One reason is that older individuals
have had more opportunities to be exposed to harmful environmental factors.
Sometimes a cumulative effect develops; an excellent example is the effect of
sunlight.
Another reason is that the elderly
more often have a decline in the functioning of body
systems on which the integumentary system depends. For example, the ability of
the nervous system to control the size of dermal blood vessels diminishes with
age, further reducing the ability of the skin to regulate body temperature. A
third reason is the increasing incidence of diseases in body systems on which
the skin relies. A common example is circulatory system diseases such as
atherosclerosis, which reduces blood supply to the skin. The skin then becomes
thinner, weaker, and more susceptible to injury and infection.
Another effect of such factors is
that the elderly have a higher incidence of abnormal
changes in the integumentary system. Studies have shown that up to 40 percent
of otherwise healthy individuals between ages 65 and 74 have at least one skin
disorder serious enough to require treatment. Many of these individuals have
more than one skin disorder at the same time. It is noteworthy that all these
disorders can also be found at least occasionally in the young.
Though almost none of these
abnormalities are fatal and almost all are preventable or treatable, they are
important in several ways. First, some integumentary system problems alter the
structure and functioning of the integument so that it is less able to perform
its usual functions. For example, bedsores increase the risk of infection.
Second, some problems produce a considerable degree of discomfort. For example,
excessively dry skin causes intense itching, which can be so distracting that
it disrupts normal daily activities. Finally, some problems, such as excessive
wrinkling from prolonged exposure to sunlight, adversely affect the appearance
of the skin.
Sunlight can cause many skin abnormalities.
For example, exposure to very strong sunlight for even a few hours can cause
sunburn. However, of more concern here are problems that take years to develop
because each exposure advances the problem only slightly. The results are
apparent only after they have accrued for decades. They are so subtle and
widespread that until recently they were widely thought to be age changes. Many
researchers believe that the ultraviolet light in sunlight causes these long‑term
effects, but other components of sunlight may be more to blame. Energy from UV
light damages DNA directly, and UV light promotes free radical (*FR) production
in the skin while reducing its *FR defenses. Even short doses (e.g., minutes)
of low intensity UV light, which is not enough to cause skin reddening, causes
damage to fibroblasts and increases elastin synthesis. Smoking increases the
adverse effects from sunlight, probably by reducing blood flow to the skin and
by increasing *FR production. Certain cosmetics, medications, and chemical air
pollutants also increase *FR formation by UV light.
Chronic exposure to sunlight affects
the epidermis in several ways. The keratinocytes reproduce irregularly, and the
new cells produced are uneven in shape. This makes the epidermis appear to be
uneven in thickness and rough in texture. The irregularity of the cells also
seems to contribute to the higher incidence of epidermal skin cancer in the
elderly. In addition, the melanocytes become more unevenly distributed,
increasing the number of age spots and intensifying the blotchy appearance of
the skin. Langerhans cells decrease in number, leading to a reduction in their
defense capability. Finally, sweat gland function declines.
The dermis is also changed by years
of exposure to sunlight. There is a net loss in collagen, and the remaining
collagen becomes weaker. Elastin fibers become more numerous but also become
very irregular in shape and arrangement from excess cross-links, and many
develop unusual thickenings. Production of abnormal molecular complexes in the
gel reduce its ability to hold water. These changes may be a main reason for
the excessive wrinkling of sun‑exposed skin.
Unlike elastin fibers, dermal blood
vessels in sun‑exposed skin decrease in number, leading to a reduced
blood supply to the skin. The capillaries that remain have thicker walls, and
this may further reduce the vital movement of material between the blood and
skin cells. In addition, certain materials, such as topically applied chemicals
and antibodies produced by the immune cells, tend to accumulate within the
skin. These materials can injure and irritate the skin, leading to discomfort
and blistering.
Sunlight also affects the sebaceous
glands, causing them to enlarge considerably. Some become so large that they become
visible as unattractive comedones (blackheads).
Obviously, all the effects of long‑term
exposure to sunlight are detrimental. All can be prevented by shading the skin
from repeated and prolonged exposure to sunlight. This can be done easily by
wearing appropriate clothing, hats, and sun screen lotions that block most of
the harmful rays. Protection while in water is also important because water
blocks only some UV light. Sun screen lotion with an SPF15 is adequate to
absorb almost all harmful UV light. Lotions with higher SPF provide very little
additional protection. The benefits from protecting skin from excess sunlight
include more attractive and healthier skin and a reduced risk of cancer.
It may be possible to prevent UV and
other types of oxidative damage to the skin by using topical or oral
supplements to increase the skin's *FR defenses. Research suggests that the
best method may be a combination of oral supplements of selenium, vitamin C,
vitamin E, and β-carotene. Supplements must be used carefully to avoid
some toxic effects and to prevent additional *FR formation by unbalancing *FR
defenses.
Treatments for cosmetic effects from
photoaging of skin include alpha-hydroxy acid peels (e.g., glycolic acid),
carbon dioxide laser treatment, and cryotherapy for epidermal color problems. Glycolic
acid treatment requires months of regular applications and visits to a
dermatologist's office. Beneficial may include smoothing and thickening of the
epidermis; reduction in comedones, small wrinkles,
and age spots; and thickening of the dermis. Undesirable side effects can
include redness, itching, burning, scabbing, pain, and tightness, which may
take from a few days to a week to subside after each treatment. Other possible
problems include scarring and reactivation or spreading of Herpes I sores and
warts.
Topical application of a vitamin A
derivative called tretinoin (i.e., all-trans tretinoic acid) can help reverse the effects of
photoaging, and it also reverses normal age changes. Benefits in the epidermis
include thicker, smoother, and more dense epidermis; reduction in abnormal
keratinocytes and uneven skin color (e.g., age spots); and faster healing when
used for weeks or months before surgery or injury. Thickening of the epidermis
is temporary. Benefits in the dermis include increases in normal collagen; in
capillaries; in dermal vessels dilation; in number and length of dermal
papillae; and in attachment of the dermis to the epidermis. Tretinoin treatment
also reverses normal age changes and adverse effects from reduced blood flow.
Tretinoin seems to act by
stimulating DNA synthesis and tissue growth factors. There seems to be no risk
of abnormal cells, precancerous cells, or cancer. The new cells seem to be even
more "normal" than the normal but somewhat altered keratinocytes and
melanocytes in photoaged skin.
Tretinoin may be applied topically
or by injections. A combination of injections plus topical treatment may be
best in some situations. Treatment can cause some temporary redness and
discomfort, and treatments may require months to complete.
Chronic exposure to heat produces
the same effects as photoaging except that chronic heat does not cause
formation of excess and abnormal elastic fibers. Chronic exposure to heat can
occur in work places, in unevenly heated living spaces, and when using
localized heaters (e.g., heating pads).
Another largely preventable skin
problem is bedsores (decubitus ulcers), patches of
skin that have died because they received insufficient blood flow. The main
cause is pressure, which compresses the blood vessels in the skin so that
little or no blood flows through them. If blood flow is reduced for more than 2
hours at a time, the skin cells die and peel away, leaving an open wound (Fig.
3.4 ).
Many factors contribute to the
formation of bedsores. Because the elderly are more
likely than the young to encounter many of these factors at more intense
levels, there is an increased incidence of bedsores among the elderly. The most
important of these factors is immobility, because the weight of the body puts
enough pressure on the skin to cut off blood flow through skin vessels. The
most susceptible parts of the body are the buttocks and the heels because
sitting or lying puts pressure on these areas. The elderly are
more likely to find themselves in these positions for long periods because of
disabling diseases such as strokes.
Other factors that increase the
possibilities of developing bedsores include normal weakening of the skin;
thinning of the subcutaneous fat; diseases of the circulatory system that
reduce blood flow; poor nutrition; and poor skin hygiene. All these factors are
more prevalent among the elderly. Physical forces on the skin, such as friction
and uneven distribution of weight, also contribute to the formation of
bedsores.
Once a bedsore has formed, it may
become deeper and penetrate through the dermis and the subcutaneous layer.
Bedsores heal very slowly if at all. Those that heal are likely to recur.
Bedsores often become infected because
the barrier against microbes has been broken. The reduced blood flow also
leaves the skin with weak defense mechanisms. Finally, bedsores can be quite
painful and can be repugnant for care givers and others.
With proper preventive measures,
bedsores can be largely avoided. Frequent changes in position, the use of soft
supporting materials that distribute body weight evenly, and good hygiene can
greatly reduce the occurrence of these undesirable skin afflictions.
Sometimes the production of new
cells in the skin gets out of control. Instead of producing the number of cells
needed and then stopping, cell production continues unabated. This condition is
called a neoplasm. If the extra cells stay tightly together in one
place, the mass is called a benign neoplasm (Fig.
3.5 ).
This type of neoplasm is usually not very harmful. However, if the cells begin
to spread out or move to other parts of the body, they constitute a malignant
neoplasm or cancer (Fig.
3.5 ).
Cancer is much more likely to cause serious problems because it disrupts the
structure and functioning of any body part it invades.
In the skin, both types of neoplasm
occur considerably more frequently as people get older. Furthermore, the
elderly have more cases of cancer of the skin than
cases of all other forms of cancer combined.
There are many reasons for the high
incidence of skin neoplasms among the elderly, and they correlate with other
age‑related changes in the skin. These changes include age changes such
as (1) increased irregularity in the cells produced, (2) reduced number of
Langerhans cells, (3) decreased amounts of melanin, (4) a decreased
inflammatory response, which can warn of the presence of noxious carcinogens,
and (5) slower removal of materials such as carcinogens. Note that all these
changes are amplified by exposure to sunlight and that sunlight itself causes
neoplasms. Therefore, protecting the skin from long‑term exposure to
sunlight can significantly reduce the risk of developing skin neoplasms.
Benign
Skin Neoplasms Common
benign neoplasms of the elderly include basal cell papilloma,
also called actinic keratosis, keratoses, senile warts, and seborrheic warts,
appearing as round somewhat elevated flattened darker spots; squamous
papilloma and clear cell acanthoma, appearing as small
round elevations. Other benign neoplasms of the skin usually appear as small
protrusions of the epidermis. These neoplasms are usually only of cosmetic
importance and can be easily removed with simple surgical procedures. Removal
may be desirable for cosmetic reasons and to avoid possible injury to the
protruding skin, which could lead to discomfort and infection. Finally, removal of benign
neoplasms is often recommended because they may become malignant.
Malignant Skin Neoplasms
Common malignant skin neoplasms include basal cell carcinoma
and squamous cell carcinoma. The first type is the most common.
It appears as a slow growing light-colored spot, which develops into a sore
that will not heal. Squamous cell carcinoma appears as thickened areas with
irregular surfaces. Both types develop from keratinocytes. Because their cells
are not well attached to each other, these malignant neoplasms can weaken the
skin, greatly increasing the risk of injury and infection. As they spread, they
affect larger areas of the skin. Fortunately, they are easily detected while
still in the early stages of growth and can then be removed by means of simple
surgery.
Malignant melanoma is a third type of skin cancer. It
is usually caused by exposure to sunlight. Malignant melanoma derives from the
melanocytes, and often appears as dark irregular mottled spots that enlarge.
Though less common than the other two skin cancers, it is a very serious and
often life‑threatening cancer. It grows very rapidly and spreads quickly
to many other organs. Wherever it is found, it displaces the normal cells in
the area, causing that part of the body to stop functioning normally. It also
weakens body parts so that there is an increased risk of infection. Malignant
melanoma can be cured if it is removed before it enlarges and spreads.
Melanoma causes more deaths from
skin cancer than all other types of skin cancer combined. The number and rates
of death from melanoma have increased several fold
over the passed 50 years, including among the
elderly. Still, the elderly have a greater age-related
increase in deaths from non-melanoma skin cancers and a greater total mortality
from non-melanoma skin cancers than from malignant melanoma. This trend may
result from earlier deaths of those most susceptible to melanoma.
Since skin cancers can become
dangerous quickly, early detection and treatment are essential. Knowing the
warning signs of skin cancer and noticing them when they appear can help. The
signs include any unusual lump or thickening, any sore or wound that does not
heal quickly, the appearance of dark spots, and any change in the shape or size
of a wart, mole, or other dark spot. Any dark spot that develops a rough
texture or an irregular outline is especially noteworthy. All suspicious areas
should be reported immediately to a physician for further diagnosis and
appropriate treatment.
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Copyright 2020: Augustine G. DiGiovanna, Ph.D.,
Salisbury University, Maryland
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