272
UNIT 2
Covering, Support, and Movement of the Body
8
because estrogens increase the rate of its excretion). Because gout
seems to run in families, genetic factors are definitely implicated.
Untreated gout can be very destructive; the articulating bone
ends fuse and immobilize the joint. Fortunately, several drugs (col-
chicine, nonsteroidal anti-inflammatory drugs, glucocorticoids,
and others) that terminate or prevent gout attacks are available. Pa-
tients are advised to drink plenty of water and to avoid alcohol ex-
cess (which promotes uric acid overproduction), and foods high in
purine-containing nucleic acids, such as liver, kidneys, and sardines.
Lyme Disease
Lyme disease
is an inflammatory disease caused by spirochete bacte-
ria transmitted by the bite of ticks that live on mice and deer. It o±en
results in joint pain and arthritis, especially in the knees, and is char-
acterized by a skin rash, flu-like symptoms, and foggy thinking. If
untreated, neurological disorders and irregular heartbeat may ensue.
Because symptoms vary from person to person, the disease is
hard to diagnose. Antibiotic therapy is the usual treatment, but
it takes a long time to kill the infecting bacteria.
Check Your Understanding
12.
What does the term “arthritis” mean?
13.
How would you determine by looking at someone suffering
from arthritis if he or she has OA or RA?
14.
What is the cause of Lyme disease?
For answers, see Appendix H.
Developmental Aspects
of Joints
Discuss factors that promote or disturb joint homeostasis.
As bones form from mesenchyme in the embryo, the joints de-
velop in parallel. By week 8, the synovial joints resemble adult
joints in form and arrangement, and synovial fluid is being se-
creted. During childhood, a joint’s size, shape, and flexibility are
modified by use. Active joints have thicker capsules and liga-
ments, and larger bony supports.
Injuries aside, relatively few interferences with joint func-
tion occur until late middle age. Eventually advancing years take
their toll and ligaments and tendons shorten and weaken. Te
intervertebral discs become more likely to herniate, and oste-
oarthritis rears its ugly head. Many people have osteoarthritis
by the time they are in their 70s. Te middle years also see an
increased incidence of rheumatoid arthritis.
Exercise that coaxes joints through their full range of motion,
such as regular stretching and aerobics, is the key to postponing the
immobilizing effects of aging on ligaments and tendons, to keeping
cartilages well nourished, and to strengthening the muscles that sta-
bilize the joints. Te key word for exercising is “prudently,” because
excessive or abusive use of the joints guarantees early onset of os-
teoarthritis. Te buoyancy of water relieves much of the stress on
weight-bearing joints, and people who swim or exercise in a pool
o±en retain good joint function as long as they live. As with so many
medical problems, it is easier to prevent joint problems than to cure
or correct them.
that destroy body tissues when released inappropriately in large
amounts as in RA. Synovial fluid accumulates, causing joint
swelling, and in time, the inflamed synovial membrane thick-
ens into a
pannus
(“rag”), an abnormal tissue that clings to the
articular cartilages. Te pannus erodes the cartilage (and some-
times the underlying bone) and eventually scar tissue forms and
connects the bone ends. Later this scar tissue ossifies and the
bone ends fuse together, immobilizing the joint. Tis end condi-
tion, called ankylosis (ang
0
kĭ-lo
9
sis; “stiff condition”), o±en pro-
duces bent, deformed fingers
(Figure 8.15)
. Not all cases of RA
progress to the severely crippling ankylosis stage, but all cases do
involve restriction of joint movement and extreme pain.
A wonder drug for RA sufferers is still undiscovered. Te goal
of current RA treatment is to go beyond simply alleviating the
symptoms and instead to disrupt the relentless destruction of
the joints by the autoimmune processes. Steroidal and nonster-
oidal anti-inflammatory drugs decrease pain and inflammation,
increasing joint mobility. More powerful immune suppressants
(such as methotrexate) act to slow the autoimmune reaction.
Several biologic agents are available to block the action of in-
flammatory chemicals. An important target of many of these
agents is an inflammatory chemical called
tumor necrosis factor
,
an important contributor to destruction of cartilage. ²ogether,
these drugs can dramatically slow the course of RA. As a last
resort, replacing the joint with a joint prosthesis (artificial joint),
may be an option to restore function (see
A Closer Look
, p. 271).
Indeed, some RA sufferers have over a dozen artificial joints.
Gouty Arthritis
Uric acid, a normal waste product of nucleic
acid metabolism, is ordinarily excreted in urine without any
problems. However, when blood levels of uric acid rise exces-
sively (due to its excessive production or slow excretion), it may
be deposited as needle-shaped urate crystals in the so± tissues
of joints. An inflammatory response follows, leading to an ago-
nizingly painful attack of
gouty arthritis
(gow
9
te), or
gout
. Te
initial attack typically affects one joint, o±en at the base of the
great toe.
Gout is far more common in men than in women because
men naturally have higher blood levels of uric acid (perhaps
Figure 8.15
A hand deformed by rheumatoid arthritis.
Inflammation has enlarged the synovial joints.
previous page 306 Human Anatomy and Physiology (9th ed ) 2012 read online next page 308 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off