Skeletal Structure Changes with Aging
the effects of aging on bones.
what happens as joints age.
one constantly remodels itself. At any given
time, the amount of bone mass in your body is
related to the rates at which your osteoblasts
make bone and your osteoclasts resorb bone.
Bone Mass Decreases As You Get Older
From birth through adolescence, you make more bone
than you lose. Young adults make as much bone as they
lose. From middle age onward, you begin to lose more bone
than you replace; this is especially true for women due to
the loss of sex hormones such as
estrogen after menopause. These
changes in the balance of bone
creation and resorption result in
two major effects of aging on bone:
Bones become more brittle—Rates ofprotein synthesis
and production of collagen fibers decrease, probably
due to diminished growth hormone production. (Recall
that protein fibers give bone its flexibility.)
Bones lose mass—Increased osteoclast activity with
age causes bones to lose minerals, mostly calcium. The
mineral extracellular matrix gives bone its strength.
This usually begins around age 30, increases around age
45, and continues throughout the rest of life. By age 70,
as much as 30% of bone mass is lost.
Age-related demineralization of bone affects 60 million
people in the United States each year, mostly middle-aged
and elderly women. In the condition known as osteoporosis
(os'-te-o-po-RO-sis), so much mineral has been removed
from the bone matrix that the bones become porous
(Figure 5.17). This loss of minerals makes the bones weak
and susceptible to fractures. Weight-bearing bones such as
the spine, hip, and femur are especially prone to injury.
A diagnosis of osteoporosis is usually made based on
a combination of factors: family history of the condition,
small skeletal stature, and a bone mineral density (BMD)
test indicating a decreased mineral composition of the
bone. Treatment includes diets high in calcium and vita-
min D, exercise, and medications.
pawz) The termination
of the menstrual or
O ste o p o ro sis • Figure 5.17
Comparing spongy bone tissue from a normal young adult (
) with that of a person
with osteoporotic bone (
) shows how the bone tissue has lost minerals and become
porous. Osteoporosis affects both spongy bone tissue and compact bone tissue.
144 CHAPTER 5
The Skeletal System