Reproductive System
The sixty-year-old may experience minor memory losses.
A few million of the person’s billions of brain cells have been
lost over his or her lifetime, but for the most part, intellect
remains sharp. By age seventy, height decreases a full inch
(2.5 centimeters). Sagging skin and loss of connective tis-
sue, combined with continued growth of cartilage, make the
nose, ears, and eyes more prominent.
ens) is the process of growing old. It is
a continuation of the degenerative changes that begin dur-
ing adulthood. The body becomes less able to cope with the
demands placed on it by the individual and by the environ-
Senescence is a result of the normal wear-and-tear of
body parts over many years. For example, the cartilage cov-
ering the ends of bones at joints may wear away, leaving
the joints stiff and painful. Other degenerative changes are
caused by disease processes that interfere with vital func-
tions, such as gas exchanges or blood circulation. Metabolic
rate and distribution of body fl
uids may change. The rate of
division of certain cell types declines, and immune responses
weaken. The person becomes less able to repair damaged tis-
sue and more susceptible to disease.
Decreasing efficiency of the central nervous system
accompanies senescence. The person may lose some intel-
lectual functions. Also, the physiological coordinating capac-
ity of the nervous system may decrease, and homeostatic
mechanisms may fail to operate effectively. Sensory func-
tions decline with age also.
Death usually results, not from these degenerative
changes, but from mechanical disturbances in the cardio-
vascular system, failure of the immune system, or disease
processes that affect vital organs.
Table 23.9
summarizes the
major phases of postnatal life and their characteristics, and
table 23.10
lists some aging-related changes.
From 65% to 80% of all deaths in the United States take place in hos-
pitals, often with painful and sometimes unwanted interventions to
prolong life. One study found that about half of conscious patients
suffer severe pain prior to death. In Oregon, which has pioneered
education on caring for the dying patient and allows assisted suicide,
a greater percentage of patients live out their last days at home; in
nursing homes; or in hospices, facilities dedicated to providing com-
fort and support for the dying. The medical community is trying to
remedy shortcomings in the treatment of the dying. Medical training
is increasing emphasis on providing palliative care for the terminally
ill. Such care seeks to make a patient comfortable, even if the treat-
ment does not cure the disease or extend life.
The End of Life
Nearing the end of life is a personal process, infl
uenced by
belief as well as circumstance. However, if the person has
remain thin. In addition to energy sources, foods must pro-
vide ample amounts of proteins, vitamins, and minerals
to support growth of new tissues. Adolescence also brings
increasing levels of motor skills, intellectual ability, and
emotional maturity.
(maturity) extends from adolescence to old age.
As we age, we become gradually aware of certain declining
functions—yet other abilities remain adequate throughout
life. The “Life-Span Changes” sections in previous chapters
have chronicled the effects of aging on particular organ sys-
tems. It is interesting to note the peaks of particular struc-
tures or functions throughout an average human life.
By age eighteen, the human male is producing the most
testosterone that he will ever have, and as a result his sex
drive is strong. In the twenties, muscle strength peaks in
both sexes. Hair is at its fullest, each hair its thickest. By the
end of the third decade of life, obvious signs of aging may
± rst appear as a loss in the elasticity of facial skin, producing
small wrinkles around the mouth and eyes. Height is already
starting to decrease, but not yet at a detectable level.
The age of thirty seems to be a developmental turning
point. After this, hearing often becomes less acute. Heart
muscle begins to thicken. The elasticity of the ligaments
between the small bones in the back lessens, setting the
stage for the slumping posture that becomes apparent in later
years. Some researchers estimate that beginning roughly at
age thirty, the human body becomes functionally less ef± -
cient by about 0.8% every year.
During their forties, many people weigh 10 to 20 pounds
(4.5 to 9 kilograms) more than they did at the age of twenty,
thanks to a slowing of metabolism and decrease in activ-
ity level. They may be 1/8 inch (0.3 centimeter) shorter,
too. Hair may be graying as melanin-producing biochemical
pathways lose ef± ciency, and some hair may fall out. Vision
may become farsighted. The immune system is less ef± cient,
making the body more prone to infection and cancer. Skeletal
muscles lose strength as connective tissue appears within
them; the cardiovascular system is strained as the lumens of
arterioles and arteries narrow with fatty deposits; skin loosens
and wrinkles as elastic ± bers in the dermis break down.
The early fifties bring further declines. Nail growth
slows, taste buds die, and the skin continues to lose elastic-
ity. For most people, the ability to see close objects becomes
impaired, but for the nearsighted, vision improves. Women
stop menstruating, although interest in sex continues (see
chapter 22, pp. 860–861). Delayed or reduced insulin release
by the pancreas, in response to a glucose load, may lead to
diabetes. By the decade’s end, muscle mass and weight begin
to decrease. A male produces less semen but is still sexu-
ally active. His voice may become higher as his vocal cords
degenerate. A man has half the strength in his upper limb
muscles and half the lung function as he did at age twenty-
± ve. He is about 3/4 inch (2 centimeters) shorter.
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