racing biker feels that he needs an edge so that
he can get a better time on each leg of the Tour
de France. A baseball player wants to hit more home
runs. A championship track star wants to break a world
record. In many instances, athletes such as these have
turned to performance-enhancing drugs to achieve
their goals.
Many performance-enhancing drugs are actu-
ally natural chemicals called hormones. For example,
erythropoietin is a hormone that signals the bone mar-
row to make more red blood cells, which increases the
ability of the blood to carry oxygen to working muscles.
Because it increases oxygen-carrying capacity, it en-
hances an athlete's endurance. Human growth hormone
and steroid hormones, such as testosterone, increase
the growth of skeletal muscles. Increased muscle mass
enables athletes to run faster and become stronger.
Unfortunately, these performance-enhancing drugs
can have harmful side effects, not to mention the unfair
competitive advantage they may give athletes. Many
athletic agencies such as the International Olympic
Committee, National Baseball League, and National
Football League forbid players from using these sub-
stances. Furthermore, athletes must submit blood and
urine samples periodically to be tested for banned sub-
stances. The consequences for using these substances
can be severe. In some cases, athletes even face crimi-
nal charges for using and distributing these substances.
In addition to the hormones that enhance perfor-
mance, the body produces many hormones
that are necessary for normal functions. Let's look at
the various hormones that the body produces, how
the endocrine system uses them, and their
physiological functions.
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