THYROID, ANTITHYROID, AND PARATHYROID PREPARATIONS
Section I. OVERVIEW
The thyroid gland is a very important endocrine gland. This gland is located in
the neck just below the larynx. This gland secretes the hormone thyroxin. Proper
functioning of the thyroid gland is essential to normal functioning of the body. Either
increased or decreased thyroid activity can present real problems to the patient. This
lesson will focus attention on the thyroid gland and present some of the drugs available
to treat both hypoactivity and hyperactivity of this important endocrine gland.
THE NATURAL THYROID HORMONES
Two hormones are responsible for the major functions of the thyroid. These
hormones are thyroxine (T4) and triiodothyronine (T3). The notation T4 reflects that the
thyroxine nucleus has four iodine atoms attached to it. The notation T3 means that
three iodine atoms are attached to the thyroxine nucleus. Approximately, 10 times as
much T4 is secreted from the thyroid than T3. As the T4 circulates, some of it has iodine
removed from the molecule. Hence, in terms of availability to body tissues, only about
three times as much T4 is available than T3. Basically, because of differences in serum
concentration and activity, the effects produced by these two hormones are identical for
practical purposes. In order for these hormones to be synthesized in the body, sources
of iodine must be present. When sufficient iodine is lacking in the diet, endemic goiters
(enlarged thyroid) result. Such enlargement is due to hypersecretion of thyroid
stimulating hormone (TSH) in an attempt by the body to obtain the required level of
thyroid hormone secretion.
FUNCTION OF THE THYROID HORMONES
The hormones produced by the thyroid gland exert effects on most of the tissues
of the body. Basically, the thyroid hormones maintain normal metabolic rate, allow the
body to more rapidly use carbohydrates for energy, and promote the growth of tissues
in the body.
Hypothyroidism occurs when there is not enough thyroxin being secreted into the
bloodstream. Depending on the age of the individual affected, various problems can
result because of hypothyroidism.