240
UNIT TWO
Falls among the elderly are common and have many
causes (see
table 7.12
). The most common fractures, after
vertebral compression and hip fracture, are of the wrist, leg,
and pelvis. Aging-related increased risk of fracture usually
begins at about age ±
fty. Healing is slowed, so pain from a
broken bone may persist for months. To preserve skeletal
health, avoid falls, take calcium supplements, get enough
vitamin D, avoid carbonated beverages (phosphates deplete
bone), and get regular exercise.
PRACTICE
40
Why is bone lost faster with aging than it is replaced?
41
Which bones most commonly fracture in the elderly?
the third decade of life, bone matrix is removed faster than it
is laid down. By age thirty-± ve, we start to lose bone mass.
Trabecular bone, due to its spongy, less compact nature,
shows the changes of aging ±
rst, as it thins, increasing in
porosity and weakening the overall structure. The verte-
brae consist mostly of trabecular bone. It is also found in the
upper part of the femur, whereas the shaft is more compact
bone. That trabecular bone weakens sooner than compact
bone destabilizes the femur, which is why it is a commonly
broken bone among the elderly.
Compact bone loss begins at around age forty and con-
tinues at about half the rate of loss of trabecular bone. As
remodeling continues throughout life, older osteons dis-
appear as new ones are built next to them. With age, the
osteons may coalesce, further weakening the overall struc-
tures as gaps form.
Bone loss is slow and steady in men, but in women, it is
clearly linked to changing hormone levels. In the ±
rst decade
following menopause, 15% to 20% of trabecular bone is
lost, two to three times the rate of loss in men and premeno-
pausal women. During the same time, compact bone loss is
10% to 15%, three to four times the rate of loss in men and
premenopausal women. By about age seventy, both sexes
are losing bone at about the same rate. By very old age, a
woman may have only half the trabecular and compact bone
mass as she did in her twenties, whereas a very elderly man
may have one-third less bone mass.
TABLE
7.12
|
Possible Reasons for Falls
Among the Elderly
Overall frailty
Decreased muscle strength
Decreased coordination
Side eF
ects of medication
Slowed reaction time due to stiF
ening joints
Poor vision and/or hearing
Disease (cancer, infection, arthritis)
3. Microscopic structure
a. Compact bone contains osteons cemented together.
b. Central canals contain blood vessels that nourish
the cells of osteons.
c. Perforating canals connect central canals
transversely and communicate with the bone’s
surface and the medullary cavity.
d. Diffusion from the surface of thin bony plates
nourishes cells of spongy bones.
7.3
BONE DEVELOPMENT AND GROWTH
(PAGE 197)
1. Intramembranous bones
a. Certain fl
at bones of the skull are
intramembranous bones.
b. They develop from layers of connective tissues.
c. Osteoblasts within the membranous layers form
bone tissue.
d. Osteoblasts surrounded by extracellular matrix are
called osteocytes.
e. Relatively unspecialized connective tissue gives
rise to the periosteum.
CHAPTER SUMMARY
7.1
INTRODUCTION (PAGE 193)
Individual bones are the organs of the skeletal system. A
bone contains active tissues. Bones support and protect
soft tissues, provide attachment for muscles, house blood-
producing cells, and store inorganic salts.
7.2
BONE STRUCTURE (PAGE 193)
Bone structure refl
ects its function.
1. Bone classi±
cation
Bones are grouped according to their shapes—long,
short, fl
at, irregular, or round (sesamoid).
2. Parts of a long bone
a. Epiphyses at each end are covered with articular
cartilage and articulate with other bones.
b. The shaft of a bone is called the diaphysis.
c. Except for the articular cartilage, a bone is covered
by a periosteum.
d. Compact bone has a continuous extracellular
matrix with no gaps.
e. Spongy bone has irregular interconnecting spaces
between bony plates.
f. Both compact and spongy bone are strong and
resist bending.
g. The diaphysis contains a medullary cavity ±
lled
with marrow.
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