How do environmental hazards, developmental
processes, and genetic tendencies
contribute to the aging process? Most scientists
agree that aging is probably caused by a combination
of environmental, developmental, and
genetic factors, but they disagree on which factors
may be most important. Two theories, the wear
and tear theory and the somatic mutation theory,
emphasize the role of the environment. The wear
and tear theory, which is based on the idea that
the body is like a machine that simply wears out,
is now largely discounted. The somatic mutation
theory holds that environmental insults cause genetic
damage, which hastens aging.
Several other theories highlight the role of developmental
processes and genetic programming.
The immune function theory of aging
emphasizes the gradual breakdown of the immune
system as the central cause of aging. Another
theory, the cross-linkage theory of aging, is
based on the idea that the gradual accumulation
of cross-linked collagen causes a number of bodily
changes associated with aging, such as hardening
of the arteries and stiffness of joints. A
third theory emphasizes the role of free radicals,
unstable molecules that are implicated in a number
of diseases. Finally, according to genetic
control theory, our life span is programmed into
our genes.
What is the difference between normal
aging and pathological aging? Biological aging
refers to the structural and functional changes
that occur in an organism over time, beginning at
maturity and lasting until death. This normal
process of aging is rarely lethal on its own. Instead,
aging-dependent diseases, including cancer,
diabetes, heart disease, osteoporosis, and
Alzheimer's disease, increase a person's vulnerability
to stress and the probability of death. This
increased vulnerability is called senescence. While
disability rates increase as people age, most people
spend most of their lives free of disability.
How does aging change a person's physical
appearance and mental functioning? As we
age, a number of changes occur in the skin.
Some, such as wrinkles, sagging chins, and age
spots, have no health consequences. The risk of
skin cancer also increases with age, because of
the cumulative effects of a lifetime of exposure to
the sun. Age-related changes in the nervous system,
which coordinates all other body systems,
can affect walking, sleep patterns, learning, and
memory. As people age, they spend more time in
the lighter stages of sleep and awaken more often
during the night. Because of changing sleep patterns,
older people are more prone to chronic insomnia.
They are also more likely to fall.
How does aging affect a person's sensory
organs? As people age, they lose sensitivity to
perceptual experiences associated with vision,
hearing, taste and smell, and touch. Older people
need more light to see clearly and may have
trouble seeing in the dark. They also may have
presbyopia, which refers to an inability to focus
on near objects. Two visual disorders that become
increasingly common with advancing
years are cataracts and glaucoma. Both can be
prevented or cured with proper medical treatment.
As people age, their ability to receive and
interpret sound declines. The loss of hearing
can lead an otherwise healthy individual to become
socially isolated from family and friends.
Taste and smell being closely related, as people
lose their ability to smell distinct odors, their
sense of taste also suffers. A loss of taste in turn
affects eating habits. People who can't taste
their food may eat less and become malnourished.
Finally, the sense of touch, especially in
the fingertips, diminishes with age as does the
ability of the body to regulate heating and cooling.
As a result, older people are more affected
by heat waves or cold spells. Since most of these
changes occur gradually, most older people adjust
to them by making incremental changes in
their lifestyles.
What effects does aging have on the bones,
joints, and muscles? Bone depletion is a natural
part of aging that begins as young as age 30. One of the more serious consequences of bone
loss is osteoporosis. Those at greatest risk of osteoporosis
are small-boned postmenopausal women.
New treatments for osteoporosis promise to increase
bone density and improve the quality of life
for older women.
In both women and men, the most common
cause of disability in later life is arthritis, a disease
of the joints. Mild arthritis causes pain and
discomfort; severe forms, like rheumatoid arthritis,
can be crippling. The development of artificial
joints has restored freedom of movement to
severely arthritic persons.
Finally, as people age, their muscles atrophy
and their strength declines. Studies show that
strength training and other forms of exercise can
dramatically reduce the loss of muscle strength
in the aged.
How does aging change a person's sexual
capacity? Menopause signals the end of a
woman's fertility. The physical changes associated
with menopause include hot flashes and the
loss of natural vaginal lubrication. Hormone replacement
therapy can relieve these menopausal
symptoms, but is associated with a slightly increased
risk of breast cancer.
There is no male equivalent to menopause,
although male hormone levels do decline with
age. One problem some older men experience is
erectile dysfunction, or impotence. While some
cases of erectile dysfunction have a physical
cause, more often the cause is psychological.
What effects does aging have on the heart
and blood vessels? High blood pressure, or
hypertension, occurs when a person's arteries
become less pliable with age or are blocked by
accumulations of plaque. If the coronary artery
becomes blocked, a heart attack will ensue. A
number of medical procedures can reduce the
risk of heart attacks. Balloon angioplasty is a
technique that is used to open blocked arteries.
In coronary bypass surgery, blocked arteries are
replaced with blood vessels taken from other
parts of the body. Finally, artificial pacemakers
can be inserted in the chest to steady an irregular
heartbeat.
