Atrophy is a decrease in size or functional activity of
a part of the body (or of the entire body) due to
disease or other factors. Atrophy is usually used to
mean that a part of the body is wasting away.
Tissues, such as muscles and organs, can
experience atrophy. Muscles atrophy can be caused
by decreased use. A good example is when muscles
decrease in size as a result of wearing a cast due to
a broken bone. Muscle atrophy can also occur as a
result of decreased use from nerve damage, which
makes it difficult or impossible to move a body part.
A brain with Alzheimer's disease
shows less tissue (atrophy).
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Serious illness can also result in atrophy of muscles because the body needs to use up
the reserves of proteins in the muscles for energy. Atrophy can also be caused by
decreased blood flow to a particular area, lack of exercise, decreased overall
functioning, poor nutrition (often caused by poor blood flow) of cells that make up these
structures, and/or death of cells which then get reabsorbed in the body.

Decreased growth and reproduction of cells can lead to atrophy as can decreased cell
volume. Cell volume is the amount of space occupied by a cell. Lack of hormones can
also lead to atrophy. Hormones are natural chemicals produced by the body and
released into the blood that have a specific effect on tissues in the body. Hormones
commonly stimulate the growth of organs which is why a lack of hormones can causes
the reverse effect.
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Lack of enzymes can lead to atrophy. Enzymes are types of proteins
that help produce chemical reactions in the body, some of which lead
to growth. Another example of atrophy would be a decrease in size
of the brain or spine. Atrophy of the brain and spine occurs normally
from old age to a certain degree. However, too much atrophy of the
brain (particularly at an earlier age) indicates that a significant
problem is present.

Atrophic means pertaining to atrophy. Atrophy is also known as
atrophia. Atrophy comes from the Greek word "a" meaning "without"
and the Greek word "trophe" meaning "nourishment." Put the words
together and you have "without nourishment."