 |
| Credit: www.isteroids.com |
Atrophy is
the partial or complete wasting away of a part of the body. Causes of atrophy
include mutations (which can destroy the gene to build up the organ), poor
nourishment, poor circulation, loss of hormonal support, loss of nerve supply
to the target organ, excessive amount of apoptosis of cells, and disuse or lack
of exercise or disease intrinsic to the tissue itself. In medical practice,
hormonal and nerve inputs that maintain an organ or body part are said to have
trophic effects. A diminished muscular trophic condition is designated as
atrophy.
Atrophy is
the general physiological process of reabsorption and breakdown of tissues,
involving apoptosis. When it occurs as a result of disease or loss of trophic
support due to other disease, it is termed pathological atrophy, although it
can be a part of normal body development and homeostasis as well.
Normal development
Examples of
atrophy as part of normal development include shrinking and the involution of
the thymus
in early childhood, and the tonsils in adolescence. In old age, effects include, but
are not limited to, loss of teeth, hair, thinning of skin that creates
wrinkles, weakening of muscles, loss of weight in organs and sluggish mental
activity.
Muscle atrophies
Disuse
atrophy of muscles and bones, with loss of mass and strength, can occur
after prolonged immobility, such as extended bedrest, or
having a body part in a cast (living in darkness for the eye, bedridden for the
legs etc.). This type of atrophy can usually be reversed with exercise unless
severe. Astronauts in microgravity must exercise regularly to minimize atrophy
of their limb muscles.
There are
many diseases and conditions which cause atrophy of muscle mass. For example,
diseases such as cancer and AIDS induce a body wasting syndrome called "cachexia",
which is notable for the severe muscle atrophy seen. Other syndromes or
conditions which can induce skeletal muscle atrophy are congestive heart failure and liver
disease.
During
aging, there is a gradual decrease in the ability to maintain skeletal muscle
function and mass. This condition is called "sarcopenia",
and may be distinct from atrophy in its pathophysiology. While the exact cause
of sarcopenia is unknown, it may be induced by a combination of a gradual
failure in the "satellite cells" which help to regenerate
skeletal muscle fibers, and a decrease in sensitivity to or the availability of
critical secreted growth factors which are necessary to maintain muscle mass
and satellite cell survival.
Dystrophies,
myositis, and motor neuron conditions
Pathologic
atrophy of muscles can occur with diseases of the motor nerves, or diseases of
the muscle tissue itself. Examples of atrophying nerve diseases include Charcot-Marie-Tooth disease, poliomyelitis, amyotrophic lateral sclerosis (ALS
or Lou Gehrig's disease), and Guillain-Barré syndrome. Examples of
atrophying muscle diseases include muscular dystrophy, myotonia congenita, and myotonic dystrophy.
Changes in
Na+ channel isoform expression and spontaneous activity in muscle called
fibrillation can also result in muscle atrophy.
Gland
atrophy
The adrenal
glands atrophy during prolonged use of exogenous glucocorticoids like prednisone.
Atrophy of the breasts can occur with prolonged estrogen reduction,
as with anorexia nervosa or menopause. Testicular atrophy with prolonged use of
enough exogenous sex steroid (either androgen or estrogen) to
reduce gonadotropin secretion.
Vaginal
atrophy
In
post-menopausal women, the walls of the vagina become thinner (atrophic vaginitis). The mechanism for the
age-related condition is not yet clear, though there are theories that the
effect is caused by decreases in estrogen levels. This
atrophy, and that of the breasts concurrently, is consistent with the
homeostatic (normal development) role of atrophy in general, as after menopause
the body has no further functional biological need to maintain the reproductive
system which it has permanently shut down.
Research
One drug in
test seemed to prevent the type of muscle loss that occurs in immobile,
bedridden patients. Testing
on mice showed that it blocked the activity of a protein present in the muscle
that is involved in muscle atrophy. However,
the drug's long-term effect on the heart precludes its routine use in humans,
and other drugs are being sought.
No comments:
Post a Comment