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The
endocrine system is a complex network of glands that acts in concert
with the nervous system to control and coordinate the myriad chemical
reactions associated with storage and release of energy, growth,
maturation, reproduction, and behavior. The sheer complexity of this
system makes it vulnerable to breakdown, a fact that is reflected in
numerous and varied endocrine disorders. The endocrine system's
influence on bodily functions is so profound that many body systems
may be affected when any of these glands fails to operate
properly.
How Does the Endocrine System Work?
The endocrine system includes the pituitary,
thyroid, parathyroid, adrenals, testes, ovaries, pineal, and thymus
glands and the islet cells of the pancreas. The endocrine glands
function by releasing hormones (or chemical messengers) into the
bloodstream. These hormones trigger reactions in specific
tissues.
This network of glands is regulated by the
hypothalamus -- the area at the base of the brain where the endocrine
system meets the nervous system -- and by the pituitary gland.
Together, they generate chemical messages that stimulate the other
glands to further activity. When endocrine disorders develop, they
usually consist of either hypofunction (underactivity) or
hyperfunction (overactivity) of one or more glands. Occasionally,
inflammation or development of tumors in a gland leads to trouble as
well.
Endocrine hyperfunction and hypofunction may
have their source in the hypothalamus, the pituitary, or the target
gland itself. Chronic disorders are more common, and generally lead
to hypofunction; however, inflammation can cause acute episodic
malfunctions. Tumors more commonly occur in the glands themselves,
but can appear in other areas of the body, such as the lungs or
stomach, where they produce hormones that cause endocrine
dysfunction.
Pituitary Disorders
Hypopituitarism is characterized by
growth retardation in children, sexual immaturity, and metabolic
dysfunction. Hypopituitarism results from a deficiency of the
hormones secreted by the anterior pituitary gland. Panhypopituitarism
involves a partial or total failure of all this gland's hormones.
These two conditions can be caused by tumors; but they may also
result from certain chemicals, congenital defects, irradiation, and
changes in blood flow.
Symptoms usually develop gradually and may
include impotence, the absence of menstrual periods, infertility,
decreased sexual drive, and diabetes insipidus (a state of high
urinary output unrelated to the more common diabetes mellitus). Other
symptoms are hypothyroidism and adrenal insufficiency (Addison's
disease). Treatment consists of replacement hormones.
Hyperpituitarism results in the extreme
overgrowth of the skeleton and is often caused by a tumor. When
hyperpituitarism occurs before puberty, the entire body becomes
abnormally large. This condition is called gigantism. Post-pubertal
hyperpituitarism is called acromegaly and produces bone thickening;
this rare condition usually strikes between the ages of 30 and
50.
Other symptoms of hyperpituitarism include oily
skin, severe headaches, blurred vision, profuse sweating, a loss of
peripheral vision, nervous system impairment, and a rapid metabolism.
The head and facial features become enlarged and distorted in
hyperpituitarism, and the individual may show symptoms of
irritability, hostility, and other psychological
disturbances. Treatment consists of removing the tumor, followed by
hormone replacement if necessary.
The Major Endocrine Glands and Their Functions
- The pituitary gland, located at
the base of the brain, produces several hormones,
including antidiuretic hormone (ADH),
adrenocorticotrophic hormone (ACTH), thyroid-stimulating
hormone (TSH), growth hormone (GH), follicle-stimulating
hormones (FSH), luteinizing hormone (LH), and prolactin.
The pituitary has been called the master gland because so
many of the hormones it produces control the functions of
other glands.
- The thyroid gland, situated at the
front of the throat, secretes thyroxine (T4) and
triiodothyronine (T3), which are essential for growth and
development. These two hormones stimulate metabolism and
protein synthesis in most of the body's
tissues.
- The four parathyroid glands are
located next to the thyroid glands. The parathyroid
glands secrete parathyroid hormone (PTH), which controls
phosphorous and calcium metabolism and plays a central
role in bone development.
- The pancreas lies transversely in
the abdomen, just behind the stomach. The pancreas
secretes digestive juices into the stomach, and two
hormones -- insulin and glucagon -- into the bloodstream.
The hormones regulate glucose metabolism. Insulin
promotes use of glucose by the body's cells. Glucagon
regulates release of stored glucose into the
bloodstream.
- The adrenal glands sit atop the
kidneys and are composed of two separate parts -- the
outer cortex and the inner medulla. The adrenal cortex,
which accounts for 90 percent of the adrenals, secretes
aldosterone, which causes the kidneys to excrete
potassium and retain sodium; and cortisol,
corticosterone, and cortisone, which together help the
body resist stress; inhibit the immune response; promote
normal metabolism of proteins, fats, and carbohydrates;
and inhibit inflammation. The adrenal cortex also
secretes sex hormones. The adrenal medulla secretes
epinephrine and norepinephrine, which produce the body's
fight-or-flight response to stress.
- Men have two testes, which are
located in the scrotum outside the abdominal cavity. The
testes produce sperm and male hormones -- most notably
testosterone, which controls the development of the male
sex organs.
- Women have two ovaries, which are
situated on either side of the uterus. The ovaries
release eggs and secrete female sex hormones. Ovarian
hormones include estrogen, which mediates the development
of female sex organs and characteristics; and
progesterone, which prepares the uterus for pregnancy and
readies the breasts for lactation.
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Thyroid Disorders
Hypothyroidism occurs more frequently in
women than in men and is diagnosed most often between the ages of 40
and 50. Hypothyroidism, essentially an underproduction of thyroid
hormone, can be caused by an insufficiency of the hypothalamus, the
pituitary, or the thyroid gland itself.
An underactive thyroid gland may be the result
of surgery, inflammation, autoimmune conditions, or insufficient
iodine in the diet. Congenital defects may also cause hypothyroidism,
and the condition can be a side effect of certain drugs.
The early symptoms of hypothyroidism tend to be
vague. They include short-term memory loss, fatigue, lethargy,
unexplained weight gain, intolerance to cold, poor wound healing, and
constipation. Later signs of hypothyroidism include increased mental
instability; puffiness in the face and extremities; thin, dry hair;
loss of libido; loss of appetite; hand tremors; and abdominal
bloating. If left untreated, hypothyroidism may eventually lead to
onset of a life-threatening coma.
Hypothyroidism is treated by replacing the
thyroid hormones.
Hyperthyroidism is caused by
overproduction of thyroid hormone. In Graves' disease, the most
common form of hyperthyroidism, patients are likely to have an
enlarged thyroid, heat sensitivity, nervousness, difficulty in
concentrating, prematurely gray hair, weight loss, increased
appetite, diarrhea, palpitations, tremors, sweating, and, in some
cases, bulging eyes. Graves' disease is thought to result from an
immune-system malfunction that overstimulates the thyroid. The
disease may not become apparent until it is triggered by trauma or by
a benign tumor of the thyroid gland.
Hyperthyroidism is treated with antithyroid
drugs, surgery, and radioactive iodine. The drugs used to treat
hyperthyroidism include methimazole (Tapazole) and propylthiouracil
(PTU), which reduce thyroid activity. Surgery and radioactive iodine
are both aimed at destroying enough thyroid tissue to reduce hormone
secretion to more normal levels.
Other thyroid disorders include thyroiditis, an
inflammation of the thyroid gland, and goiter, an enlargement of the
thyroid gland.
Hypoparathyroidism results from
diseased, injured, or congenitally defective parathyroid glands.
Injury to the glands most often occurs during surgery involving
nearby tissue. Hypoparathyroidism may also be caused by the
prolonged, severe magnesium deficiency associated with
alcoholism.
Hypoparathyroidism leads to low blood
concentrations of calcium, which may cause neuromuscular
excitability, including spasms and twitching of the face, hands, and
feet; abdominal pain; hair loss; dry skin; and cataracts.
Treatment with vitamin D will usually reverse
hypoparathyroidism, although calcium supplementation is sometimes
required.
Hyperparathyroidism, usually caused by a
benign tumor, can lead to kidney problems, bone abnormalities,
brittle bones, and chronic low-back pain. People with
hyperparathyroidism also show such signs of gastrointestinal
discomfort as pain and ulcers, as well as muscle weakness,
constipation, depression, psychosis, stupor, and, sometimes, coma.
Treatment consists of surgery to remove the tumor or drugs to correct
any abnormalities the condition has caused. In some cases, no
specific therapy is required.
Disorders of the Adrenal Glands
Addison's disease (or adrenal
insufficiency) usually results from an autoimmune response that
destroys the adrenal glands. The symptoms of Addison's disease are
loss of appetite, weight loss, fatigue, weakness, vomiting, nausea,
and diarrhea. Other signs include a suntanned appearance, intolerance
for stress, and a craving for salty food. The treatment of Addison's
disease entails lifelong replacement of the steroid hormones produced
by the adrenals, usually with hydrocortisone or cortisone. Because
serious illness or injury may dramatically increase the body's need
for adrenal hormones, patients with Addison's disease should wear an
identification bracelet in case of emergency.
Cushing's syndrome results from the
over-secretion of adrenal hormones, especially cortisol, or from
taking synthetic ACTH or steroids. Excessive cortisol production is,
in turn, usually brought on by an oversupply of ACTH, possibly due to
a tumor that produces ACTH in another organ.
Common symptoms of Cushing's syndrome include
fatty deposits on the face, neck, and trunk, and purple streaking on
the skin. This syndrome also produces muscle and bone weakness, poor
wound healing, peptic ulcer, irritability, mood swings, difficulty
sleeping, high blood pressure, suppressed immune response, diabetes,
and changes in the reproductive system.
Treatment for Cushing's syndrome may include
radiation, drugs, or surgery. Metyrapone (Metopirone) and
aminoglutethimide (Cytadren) are among the medications used to reduce
cortisol production.
Source: From the PDR® Family Guide to Prescription Drugs™
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