the growth years
an overproduction of
somatotropin causes giantism while the lack of
it causes dwarfism. An overproduction after the
growth years causes acromegaly, which is
characterized by the development of abnormally
large hands, feet, and jaw.
THYROTROPIN, or the thyroid-stimulating
hormone (TSH), influences the growth, develop-
ment, and secreting activities of the thyroid gland.
GONADOTROPIN influences the gonads
(ovaries or testes) and is essential for the normal
development and functioning of both male and
female reproductive systems.
The ADRENOCORTICOTROPIC hormone
(ACTH) acts primarily on the adrenal cortex,
stimulating its growth and its secretion of cor-
ticosteroids. Removal of the pituitary leads to
rapid atrophy of the adrenal cortex.
The posterior lobe of the pituitary produces
at least two hormones, vasopressin and oxytocin.
VASOPRESSIN acts as an antidiuretic hormone
(ADH), promoting the conservation of water by
the kidney. When ADH is not produced in ade-
quate amounts, the daily urine volume is between
10 and 15 liters instead of the normal 1.5 liters.
This condition is known as diabetes insipidus.
OXYTOCIN stimulates contraction of the
muscles of the uterus, particularly during preg-
nancy. It also plays an important role in the pro-
duction of milk in the mammary glands of nurs-
The thyroid, shaped like a butterfly, lies in the
anterior part of the neck, below the larynx. It con-
sists of two lobes, one on each side of the upper
trachea, connected by a strip of tissue called the
isthmus. The thyroid secretes the iodinecontain-
ing hormone THYROXIN, which controls the
rate of cell metabolism. Excessive secretion of
thyroxin raises the metabolic rate and causes
hyperthyroidism, a condition characterized by a
fast pulse rate, dizziness, increased basal
metabolism, profuse sweating, tremors, ner-
vousness, and a tremendous appetite yet a loss of
weight. The thyroid may become enlarged.
Iodine is essential for the formation of thy-
roxin. To prevent simple goiter, iodine-containing
foods, such as vegetables, iodized salt, and
seafood, are eaten.
Hypothyroidism, on the other hand, is caused
by an insufficient secretion of thyroxin. The pa-
tient 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 there may be an enlargement of the
gland, called a simple goiter. There may also be
personality changes characterized by slow,
lethargic mental functioning. Hypothyroidism in
an infant may result in cretinism with impaired
mental and physical development.
Parathyroid glands are four small round
bodies located just posterior to the thyroid gland.
Their hormone, PARATHORMONE, regulates
the calcium and phosphorus content of the blood
and bones. The amount of calcium is important
in certain tissue activities, such as bone forma-
tion, coagulation of blood, maintenance of nor-
mal 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, and in extreme cases
death may occur, preceded by strong contraction
of the muscles (tetany) and convulsions.
Hyperparathyroidism, an excess of parathy-
roid 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 frac-
tures. The excess calcium may be deposited as
stones in the kidneys.
The adrenal glands are located on the superior
surface of each kidney, fitting like a cap. 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 hor-
mones that are of vital importance.
MINERALOCORTICOIDS are regulators of
fluid and electrolyte balance. They are sometimes
called salt and water hormone because they
regulate the excretion and absorption of sodium,
chlorine, potassium, and water.
GLUCOCORTICOIDS are 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