909
CHAPTER TWENTY-THREE
Reproductive System
PRACTICE
44
How does the body change during adolescence?
45
Def
ne
adulthood
.
46
What changes occur during adulthood?
47
What changes accompany senescence?
48
What are the signs oF preactive and active dying?
23.5
AGING
The aging process is difF
cult to analyze because of the intri-
cate interactions of the body’s organ systems. Breakdown of
one structure ultimately affects the functioning of others. The
medical F eld of gerontology examines the biological changes
of aging at the molecular, cellular, organismal, and popula-
tion levels. Aging is both passive and active.
Passive Aging
Aging as a passive process is a breakdown of structures and
slowing of functions. At the molecular level, passive aging is
seen in the degeneration of the elastin and collagen proteins
of connective tissues, causing skin to sag and muscle to lose
its F
rmness.
During a long lifetime, biochemical abnormalities accu-
mulate. Mistakes occur throughout life when DNA replicates
in dividing cells. Usually, repair enzymes correct this dam-
age immediately. But over many years, exposure to chemi-
cals, viruses, and radiation disrupts DNA repair mechanisms
so that the error burden becomes too great to be F
xed. The
cell may die as a result of faulty genetic instructions.
Another sign of passive aging at the biochemical level
is the breakdown of lipids. As aging membranes leak dur-
ing lipid degeneration, a fatty, brown pigment called lipo-
fuscin accumulates. Mitochondria also begin to break down
in older cells, decreasing the supply of chemical energy to
power the cell’s functions.
The cellular degradation associated with aging may be
set into action by highly reactive chemicals called
free radi-
cals.
A molecule that is a free radical has an unpaired elec-
tron in its outermost valence shell. This causes the molecule
to grab electrons from other molecules, destabilizing them,
and a chain reaction of chemical instability begins that could
kill the cell. ±ree radicals are a by-product of normal metabo-
lism and also form by exposure to radiation or toxic chemi-
cals. The bile pigment bilirubin protects against free radicals.
Enzymes that usually inactivate free radicals diminish in
number and activity in the later years. One such enzyme is
superoxide dismutase
(SOD).
Active Aging
Aging also entails new activities or the appearance of new
substances. Lipofuscin granules, for example, may be con-
sidered an active sign of aging, but they result from the
passive breakdown of lipids. Another example of active
Active dying presents a distinct set of signs, which might
appear only on the day before death, or might begin up to
two weeks earlier. During this phase the person sleeps often,
but can easily be awakened. Even if sleep is deep, the per-
son can hear—this is the last sense to fade. He or she may
confuse time, place, and identities. A nurse might be mis-
taken for a relative, or an adult child might not be recog-
nized. An actively dying person may go back in time, talking
to a deceased spouse, for example. Signs of agitation appear,
such as picking lint on the blanket or thrashing the arms
about. Appetite may be nil.
In active dying, the organ systems slowly shut down.
Cardiovascular signs include falling blood pressure (systolic
below 70, diastolic below 50). The pulse may race or slow, or
alternate. Poor circulation, which redirects the blood supply
to the body’s core, ushers in peripheral changes. The limbs
feel cool to the touch, and the person may note numbness.
The extremities become pale, then take on a bluish tinge. Skin
areas under pressure, such as the undersides of the limbs,
become mottled. Sensitivity to touch and pain declines.
The slowing circulation affects muscles. Poor ability to
cough and swallow causes secretions to build up in the lungs.
Secretions aren’t suctioned, because this increases their rate of
accumulation. The person can be repositioned to provide some
relief. Congestion is intermittent. One day it may be so severe
that eating is impossible; the next day breathing may ease.
Cheyne-Stokes breathing—shallow mouth-breathing inter-
spersed with increasingly long periods of apnea—is common.
The normal rate of 16 to 20 breaths per minute may speed to
more than 50, slow precipitously, perhaps pausing for 10 to
30 seconds, and then the person gasps and breathes rapidly
again. As the throat muscles relax, exhalation over the vocal
cords causes a passive moaning sound—this does not indicate
that the person is in pain. A day or two before death, breathing
may become loud—a sound called the “death rattle.”
Body temperature control changes, and the person
may have elevated body temperature or feel cold. The skin
may be alternately fl
ushed, then blue with an internal chill.
Sweating is common, and as death nears, the skin takes on a
yellowish pallor.
In the day or two before death, the signs intensify,
although a last burst of energy may occur. A bedridden person
may suddenly wish to be propped up in the living room and
see people, or, after weeks of barely eating, suddenly request
an ice cream sundae. Meanwhile, respiration and circula-
tion are slowing, and decreased oxygen delivery may cause
restlessness and agitation. The pulse becomes thready. Often
right before death the person loses control of the bladder or
bowels. Breathing becomes more irregular, with longer peri-
ods between breaths, and the lung rattling becomes louder.
Consciousness seems to fade in and out—often the eyes do not
focus and appear glassy, or may be only partially open. The
eyes may tear frequently. ±inally, the person can no longer
respond. After one, two, or three long, last breaths, the eyes
become F xed and open, the pupils dilate, the jaw relaxes, and
the mouth may slightly open. The journey of life has ended.
previous page 939 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 941 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off