Iodine is essential for the formation of thyroxin.
Simple goiter, a diffuse and painless enlargement of
the thyroid gland, was once common in areas of the
United States where the iodine content of the soil and
water was inadequate. In simple goiter, the gland
enlarges to compensate for the lack of iodine. To
prevent formation of a simple goiter, iodine-
containing foods, such as vegetables, iodized salt, and
seafood, should be eaten.
A condition known as hypothyroidism is caused
by an insufficient secretion of thyroxin. The patient
exhibits a decrease in basal metabolism, and sweating
is almost absent. There may be a weight gain and
constant fatigue. The heart rate may be slow, and a
simple goiter may form. There may also be personality
changes characterized by slow, lethargic mental
functioning. Hypothyroidism during childhood can
lead to the development of cretinism. Cretinism is a
condition characterized by retarded mental and
Parathyroid glands are four small round bodies
located just posterior to the thyroid gland (fig. 1-47).
Their hormone, parathormone (PTH), regulates the
calcium and phosphorus content of the blood and
bones. The amount of calcium is important in certain
tissue activities, such as bone formation, coagulation
of blood, maintenance of normal muscular excitability,
and milk production in the nursing mother. Diminished
function or removal of the parathyroid glands results in
a low calcium level in the blood. In extreme cases
death may occur, preceded by strong contraction of the
muscles (tetany) and convulsions.
Hyperparathyroidism, an excess of parathyroid
hormone in the blood, causes calcium levels in the
blood to become elevated by the withdrawal of
calcium from the bones, leaving the skeleton
demineralized and subject to spontaneous fractures.
The excess calcium may be deposited as stones in the
The adrenal glands are located on the superior
surface of each kidney, fitting like a cap (fig. 1-47).
They consist of an outer portion, the cortex, and an
inner portion, the medulla.
Specialized cells in the outer layer of the adrenal
cortex produce three types of steroid hormones that are
of vital importance.
ticoids are regulators of fluid and electrolyte balance.
They are sometimes called salt and water hormones
because they regulate the excretion and absorption of
sodium, chlorine, potassium, and water.
essential to metabolism. They increase certain liver
functions and have an anti-inflammatory effect.
Clinically, they are used to suppress inflammatory
reactions, to promote healing, and to treat rheumatoid
ANDROGENS AND ESTROGENS.The
adrenal cortex also produces sex hormones, some with
male characteristics (androgens), others with female
characteristics (estrogens). These hormones appear in
different concentrations in both men and women.
The adrenal medulla secretes epinephrine
(adrenalin) in the presence of emotional crises,
hypoglycemia (low blood sugar), or low blood
pressure. Epinephrine causes powerful contractions of
many arterioles (especially in the skin, mucous
membranes, and kidneys), but it dilates other arterioles
(such as those of the coronary system, skeletal
muscles, and lungs). Heart rate, respiration rate and
depth, blood pressure, blood sugar levels, and
metabolism are all increased by epinephrine. It also
stimulates the production of other adrenal cortical
Norepinephrine is also produced in the adrenal
medulla. It is a chemical precursor to epinephrine. Its
effects are similar to those of epinephrine, but its action
Despite these marked influences, the medullary
tissue of the adrenal gland is not essential to life,
because its various functions can be assumed by other
The pancreas contains two types of secretory
tissues. The first secretory tissue secretes digestive
juice through a duct to the small intestine, while the
other tissue releases hormones into body fluids. The