AGENESIS
A
who are too small and who may sub-
sequently have problems as a result of
their low birthweight.
In children, bone age (the degree of
bone maturity as seen on an
X-ray)
can
be a useful measure of physical devel-
opment because all healthy individuals
reach the same adult level of skeletal
maturity and each bone passes through
the same sequence of growth. Assess-
ment of bone age is useful in the
investigation of delayed
puberty
or
short
stature
in children. A prediction of the
final adult height can be made if the
chronological age, bone age, and cur-
rent height are known.
Dental age, which is another measure
of physical maturity, can be assessed
by the number of teeth that have erup-
ted (see
eruption of teeth)
or by the
amount of dental calcification (see
calci-
fication, dental),
as seen on an X-ray,
compared with standard values.
In adults, physical age is difficult to
assess other than by physical appear-
ance. It can be estimated after death by
the state of certain organs, particularly
by
the
amount
of atheroma
(fatty
deposits) lining the arteries.
MENTAL AND DEVELOPMENTAL AGE
Mental age can be assessed by the com-
parison of scores achieved in
intelligence
tests
with standard scores for different
chronological ages. A young child’s age
can be expressed in terms of his or her
level of developmental skills, manual
dexterity,
social skills,
and language
when compared to those of other chil-
dren. Patterns of development in these
fields have been described for children
up to the age of five. (See also
child
development.)
agenesis
The complete absence, at birth, of an
organ or a component of the body. Age-
nesis is caused by developmental failure
in the embryo.
agent
Any substance or force capable of bring-
ing about a biological, chemical,
or
physical change. (See also
reagent.)
Agent Orange
A herbicide and defoliant of which the
major constituent (5 0 per cent by vol-
ume) is the phenoxy acid herbicide
2,4,5 T. The highly toxic contaminant
TCDD, commonly known as dioxin,
may be added to this substance during
manufacture (see
defoliant poisoning).
age spots
Blemishes that appear on the skin with
increasing age. The most common type
are brown or yellow slightly raised
spots
called
seborrhoeic
keratoses,
which can occur at any site. Also com-
mon in elderly people are freckles, solar
keratoses
(small scaly patches,
often
appearing on the backs of the hands,
that are a result of overexposure to the
sun), and
De Morgan’s spots,
which are
red, pinpoint blemishes on the trunk.
THE PRACTICAL EFFECTS OF AGING
In the body, aging is associated with loss of elasticity in the skin, blood vessels,
and tendons. There is also progressive decline in the functioning of organs such
as the lungs, kidneys, and liver. Mechanical wear and tear causes cumulative
damage to certain organ systems. Brain cells, specialized kidney units, and many
other body structures are never replaced after they have reached maturity.
Hip joint in a
young person
The X-ray shows
the rounded head
of the thigh-bone
(femur) separated
by cartilage from
the surrounding
hip socket.
Hip joint in an
elderly person
This X-ray of an
osteoarthritic
hip shows
almost complete
degeneration and
disappearance
of the cartilage
in the joint.
EFFECTS OFAGING
Organ or tissue
Natural effects
Accelerated by
Skin
Loss of elastic tissue causes skin to sag
and wrinkle. Weakened blood capillaries
cause skin to bruise more easily.
Exposure to sun;
smoking.
Brain and
nervous
system
Loss of nerve cells leads to reduction in
ability to memorize or to learn new
skills. Reaction time of nerves increases,
making responses slower.
Excessive consumption
of alcohol and other
drugs; repeated head
trauma (for example
from boxing).
Senses
Some loss of acuity in all senses, mainly
due to loss of nerve cells.
Loud noise (hearing);
smoking (smell/taste).
Lungs
Loss of elasticity with age, so that
breathing is less efficient.
Air pollution; smoking;
lackofexercise.
Heart
Becomes less efficient at pumping,
causing reduced tolerance to exercise.
Excessive use of
alcohol and cigarettes;
a fatty diet.
Circulation
Arteries harden, causing poor blood
circulation and higher blood pressure.
Lackofexercise;
smoking; poor diet.
Joints
Pressure on intervertebral discs causes
height loss; wear on hip and knee joints
reduces mobility.
Athletic injuries; being
overweight.
Muscles
Loss of muscle bulk and strength
Lackofexercise;
starvation.
Liver
Becomes less efficient in processing
toxic substances in the blood
Damage from alcohol
consumption and virus
infections
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