Pituitary Gland
The pituitary gland is sometimes called the "master gland"
because of its great influence on the other body organs. Its
function is complex and important for overall well-being.
The pituitary gland is divided into two parts, front (anterior) and
back (posterior).
The anterior pituitary produces several types of hormones:
Prolactin or PRL - PRL stimulates milk production from
a woman's breasts after childbirth and can affect sex
hormone levels from the ovaries in women and the testes
in men.
Growth hormone or GH - GH stimulates growth in childhood and is important for
maintaining a healthy body composition. In adults it is also important for maintaining
muscle mass and bone mass. It can affect fat distribution in the body.
Adrenocorticotropin or ACTH - ACTH stimulates production of cortisol by the adrenal
glands. Cortisol, a so-called "stress hormone," is vital to survival. It helps maintain blood
pressure and blood glucose levels.
Thyroid-stimulating hormone or TSH - TSH stimulates the thyroid gland to make
thyroid hormones, which, in turn, control (regulate) the body's metabolism, energy,
growth and development, and nervous system activity.
Luteinizing hormone or LH - LH regulates testosterone in men and estrogen in women.
Follicle-stimulating hormone or FSH - FSH promotes sperm production in men and
stimulates the ovaries to release eggs (ovulate) in women. LH and FSH work together to
allow normal function of the ovaries or testes.
The posterior pituitary produces two hormones:
Oxytocin - Oxytocin causes milk letdown in nursing mothers and contractions during
childbirth.
Antidiuretic hormone or ADH - ADH, also called vasopressin, is stored in the back part
of the pituitary gland and regulates water balance. If this hormone is not secreted
properly, this can lead to problems of sodium (salt) and water balance, and could also
affect the kidneys so that they do not work as well.
In response to over- or underproduction of pituitary hormones, the target glands affected by these
hormones can produce too many or too few hormones of their own, leading to hormone
imbalance. For example, too much growth hormone can cause gigantism, or excessive growth
(referred to as acromegaly in adults), while too little GH may cause dwarfism, or very short
stature.
Hypothalamus
The hypothalamus is part of the brain that lies just above the pituitary gland. It releases hormones
that start and stop the release of pituitary hormones. The hypothalamus controls hormone
production in the pituitary gland through several "releasing" hormones. Some of these are growth
hormone-releasing hormone, or (controls GH release); thyrotropin-releasing hormone, or TRH
(controls TSH release); and corticoptropin-releasing hormone, or CRH (controls ACTH release).
Gonadotropin-releasing hormone (GnRH) tells the pituitary gland to make luteinizing hormone
(LH) and follicle-stimulating hormone (FSH), which are important for normal puberty.
Thymus
The thymus is a gland needed early in life for normal immune
function. It is very large just after a child is born and weighs its
greatest when a child reaches puberty. Then its tissue is replaced
by fat. The thymus gland secretes hormones called humoral
factors. These hormones help to develop the lymphoid system,
which is a system throughout the body that help it to reach a
mature immune response in cells to protect them from invading
bodies, like bacteria.
Pineal Gland
Scientists are still learning how the pineal gland works. They
have found one hormone so far that is produced by this gland:
melatonin. Melatonin may stop the action of (inhibit) the
hormones that produce gonadotropin, which causes the ovaries
and testes to develop and function. It may also help to control
sleep patterns.
Testes
Males have twin reproductive glands, called testes, that produce
the hormone testosterone. Testosterone helps a boy develop and
then maintain his sexual traits. During puberty, testosterone helps
to bring about the physical changes that turn a boy into an adult
male, such as growth of the penis and testes, growth of facial and
pubic hair, deepening of the voice, increase in muscle mass and
strength, and increase in height. Throughout adult life,
testosterone helps maintain sex drive, sperm production, male hair
patterns, muscle mass, and bone mass.
Testicular cancer, which is the most common form of cancer for
males between ages 15 and 35, may need to be treated by surgical
removal of one or both testicles. The resulting decrease or absence
of testosterone may cause decreased sexual drive, impotence,
altered body image, and other symptoms.
Ovaries
The two most important hormones of a woman's
twin reproductive glands, the ovaries, are estrogen
and progesterone. These hormones are responsible
for developing and maintaining female sexual
traits, as well as maintaining a pregnancy. Along
with the pituitary gonadotropins (luteinizing
hormone or LH and follicle-stimulating hormone
or FSH), they also control the menstrual cycle.
The ovaries also produce inhibin, a protein that
curbs (inhibits) the release of follicle-stimulating
hormone from the anterior pituitary and helps
control egg development.
The most common change in the ovarian hormones is caused by the start of menopause, part of
the normal aging process. It also can occur when ovaries are removed surgically. Loss of ovarian
function means loss of estrogen, which can lead to symptoms of menopause including hot
flashes, thinning vaginal tissue, lack of menstrual periods, mood changes and bone loss, or
osteoporosis.
A condition called polycystic ovary syndrome (PCOS) is caused by overproduction of male
hormones in females. PCOS can affect menstrual cycles, fertility, and hormone levels, as well as
cause acne, facial hair growth, and male pattern balding.
Thyroid
The thyroid is a small gland inside the neck, located in front of
your breathing airway (trachea) and below your Adam's apple.
The thyroid hormones control your metabolism, which is the
body's ability to break down food and store it as energy and the
ability to break down food into waste products with a release of
energy in the process. The thyroid produces two hormones, T3
(called tri-iodothyronine) and T4 (called thyroxine).
Thyroid disorders result from an underactive or overactive thyroid
producing, respectively, too little or too much thyroid hormone.
Symptoms of hypothyroidism (too little hormone) include
decreased energy, slow heart rate, dry skin, constipation, and
feeling cold all the time. In children, hypothyroidism most
commonly leads to slowed growth. Infants born with hypothyroidism can have delayed
development and mental retardation if not treated. In adults, this disorder often causes weight
gain. An enlarged thyroid, or goiter, may develop.
Hyperthyroidism (too much hormone) may impact normal thyroid size and result in exophthalmic
goiter, or Grave's disease. Symptoms of this thyroid disease include anxiety, fast heart rate,
diarrhea, and weight loss. An enlarged thyroid gland (goiter) and swelling behind the eyes that
causes the eyes to push forward, or bulge out, are common.
Adrenal Glands
Each adrenal gland is actually two endocrine
organs. The outer portion is called the adrenal
cortex. The inner portion is called the adrenal
medulla. The hormones of the adrenal cortex are
essential for life. The types of hormones secreted
by the adrenal medulla are not.
The adrenal cortex produces glucocorticoids (such
as cortisol) that help the body control blood sugar,
increase the burning of protein and fat, and
respond to stressors like fever, major illness, and
injury. The mineralcorticoids (such as
aldosterone) control blood volume and help to
regulate blood pressure by acting on the kidneys
to help them hold onto enough sodium and water.
The adrenal cortex also produces some sex hormones, which are important for some secondary
sex characteristics in both men and women.
Two important disorders caused by problems with the adrenal cortex are Cushing's syndrome and
Addison's disease. Cushing's syndrome is the result of too much cortisol, and Addison's disease
occurs when there is too little cortisol.
The adrenal medulla produces epinephrine (adrenaline), which is secreted by nerve endings and
increases the heart rate, opens airways to improve oxygen intake, and increases blood flow to
muscles, usually when a person is scared, excited, or under stress.
Norepinephrine also is made by the adrenal medulla, but this hormone is more related to
maintaining normal activities as opposed to emergency reactions. Too much norepinephrine can
cause high blood pressure.
Parathyroid
Located behind the thyroid gland are four tiny parathyroid glands.
These make hormones that help control calcium and phosphorous
levels in the body. The parathyroid glands are necessary for
proper bone development. In response to too little calcium in the
diet, the parathyroid glands make parathyroid hormone, or PTH,
that takes calcium from bones so that it will be available in the
blood for nerve conduction and muscle contraction.
If the parathyroids are removed during a thyroid operation, low
blood calcium will result in symptoms such as irregular heartbeat,
muscle spasms, tingling in the hands and feet, and possibly
difficulty breathing. A tumor or chronic illness can cause too much secretion of PTH and lead to
bone pain, kidney stones, increased urination, muscle weakness, and fatigue.
Pancreas
The pancreas is a large gland behind your stomach
that helps the body to maintain healthy blood
sugar (glucose) levels. The pancreas secretes
insulin, a hormone that helps glucose move from
the blood into the cells where it is used for energy.
The pancreas also secretes glucagon when the
blood sugar is low. Glucagon tells the liver to
release glucose, stored in the liver as glycogen,
into the bloodstream.
Diabetes, an imbalance of blood sugar levels, is the major disorder of the pancreas. There are two
types of diabetes. Type I, and Type II diabetes. Type I diabetes occurs when the pancreas does
not produce enough insulin. Type II diabetes occurs when the body is resistant to the insulin in
the blood). Without enough insulin to keep glucose moving through the metabolic process, the
blood glucose level rises too high.
In Type I diabetes, a patient must take insulin shots. In Type II diabetes, a patient may not
necessarily need insulin and can sometimes control blood sugar levels with exercise, diet and
other medications.
A condition called hyperinsulinism (HI) is caused by too much insulin and leads to hypoglycemia
(low blood sugar). The inherited form, called congenital HI, causes severe hypoglycemia in
infancy. Sometimes it can be treated with medication but often requires surgical removal of part
or all of the pancreas. An insulin-secreting tumor of the pancreas, or insulinoma, is a less
common cause of hypoglycemia. Symptoms of low blood sugar include anxiety, sweating,
increased heart rate, weakness, hunger, and light-headedness. Low blood sugar stimulates release
of epinephrine, glucagon and growth hormone, which help to return the blood sugar to normal.