The human body has two types of glands, duct
glands. Duct glands (also known as exocrine
glands) are glands which have ducts (canals) which limit the area of
their secretions. Examples of duct glands are tear glands, sweat glands and
salivary glands. Ductless glands are also known as endocrine
glands. Endocrine glands release their secretions, called hormones,
into the blood stream to be carried to other locations where they take their
action. Examples of endocrine glands are: the pituitary, thyroid, parathyroids,
adrenals, pancreas, testes, and ovaries. The study of endocrine glands is called
The word hormone
was derived from the Greek word hormodezein
which means "to arouse." While many hormones do arouse to create
action in glands and organs, their primary function is to regulate glands and
The pituitary gland is called the "master
gland" because its various hormones regulate all other endocrine glands.
The pituitary gland is located in the brain near the top of the brain stem, and
is connected to the brain by a short stalk called the infundibulum.
The pituitary gland is about the size of a cherry and is divided into three
regions. Of these, the anterior (front part) lobe is the largest. The posterior
(back part) is only slightly smaller than the anterior lobe. Between the
anterior and posterior lobes is third region, the pars
intermedia. Each of these regions produces its own group of
The anterior lobe of the pituitary produces the somatotrophic
hormone, which in people is commonly called the human
growth hormone (HGH). If this hormone is produced in greater than
normal quantities, the bones grow very long. HGH acts to prevent the epiphyseal
junction from forming, thus making continued growth possible in these bones. The
result of this greater than normal production of HGH is pituitary
giantism, and they may grow to be 9 feet tall. Giantism is
accompanied by a corresponding increase in size of the internal organs. If there
is an increased secretion of HGH after the appearance of the epiphyseal line,
the long bones do not grow. However, there is growth in the bones of the face,
hands and feet. This condition is called acromegaly.
Deficiency of HGH causes pituitary dwarfism. If dwarfism is
recognized early in a child or adolescent, HGH produced through genetic
engineering can be administered causing the child to grow.
A second hormone produced by the anterior pituitary
In mammals, prolactin stimulates the production of milk in the mammary glands
which is used to nourish the young. It may also stimulate maternal behavior. A
third hormone secreted by the anterior pituitary is the thyroid
stimulating hormone. This hormone causes the thyroid gland to
function, and if this hormone is absent, the thyroid gland shuts down.
The anterior lobe of the pituitary also produces the adrenocorticotropic
hormone (ACTH). ACTH influences the amount of various corticoids produced by the cortex of the
adrenal glands. Corticoids help regulate the amount of minerals in our bodies,
as well as carbohydrate metabolism.
The anterior pituitary also produces the two gonadotrophic
hormones, the follicle-stimulating
hormone and the luteinizing
hormone. The follicle-stimulating hormone (FSH) causes both egg
cells and sperm cells to mature so that reproduction can occur. The luteinizing
hormone (LH) works with the follicle-stimulating hormone to prepare the female
body to nourish a developing child during pregnancy.
The posterior lobe of the pituitary gland secretes
two hormones, the antidiuretic
hormone (ADH) and the oxytocic
hormone. ADH controls the reabsorption of water from the kidneys
into the blood stream. If this hormone is deficient, the blood stream does not
reabsorb water from the kidneys and urine is formed in excess amounts. The
resulting disease, called diabetes
insipidus, may result in the excretion of as much as 10 gallons of
urine per day. ADH also increases blood pressure. Once it was believed that a
separate hormone, called vasopressin,
acted on the walls of arteries to produce an increase in blood pressure (hypertension);
but it was recently discovered that vasopressin is, in actuality, ADH. A
diuretic drug stimulates urination, usually by decreasing the action of ADH. By
doing this, diuretic drugs are useful in controlling high blood pressure.
The oxytocic hormone (oxytocin) causes the contractions which
lead to child-birth. The oxytocic hormone also increases blood pressure and
decreases the formation of urine during pregnancy.
The pars intermedia produces a hormone called intermedin.
Little is known of the function of this hormone in people. In fish it functions
to darken the scales.
gland is located in the approximate area of the throat, lying along
side of the larynx. It is shaped like the letter H. The thyroid gland uses iodine
and the amino acid tyrosine
to produce the hormones thyroxin
Both of these hormones function to regulate cellular metabolism. Metabolism
refers to all of the processes that make energy available to cells. As such,
these hormones regulate the conversion of glycogen (stored glucose) to glucose.
The deficiency of thyroxin results in a reduction in
the metabolism rate. This condition is called hypothyroidism. If hypothyroidism occurs
during infancy or childhood the result is called cretinism.
Cretinism is characterized by stunted physical growth and mental retardation. If
hypothyroidism occurs in an adult, it results in such symptoms as: reduced body
temperature, a decrease in blood pressure and heart rate, dryness of the hair
and skin, loss of energy, weight gain and depression. Hypothyroidism is treated
medically by administering thyroxin.
The opposite condition, hyperthyroidism, results from an
over-production of thyroxin. The symptoms of hyperthyroidism include: rapid
heart rate, increase in blood pressure, increase in metabolism (resulting in
weight-loss), oily skin, an increase in body temperature, excess sweating, and
nervousness. People suffering from hyperthyroidism may eat very large amounts of
food and still lose weight. Hyperthyroidism is treated by removing part of the
thyroid gland and by the use of drug therapies.
is an enlarged thyroid gland, which results in a swelling in the neck. A goiter
can result from either hyper or hypothyroidism, but it is more common in
hypothyroidism. A goiter is generally caused by a lack of iodine. The thyroid
stimulating hormone of the pituitary gland causes the thyroid gland to work. But
without iodine, no thyroxin is produced. The pituitary gland responds to this by
making the thyroid gland work harder and harder. Therefore, like a muscle that
you work with a barbell, the thyroid gland gets bigger. We get most of our
iodine from seafood and from vegetables grown in soil which contains iodine.
Iodine is often supplemented in the diet by including it in salt (iodized salt).
On the back side of the thyroid gland are four small
bodies known as the parathyroid
glands. These are the smallest endocrine glands. The parathyroid
glands produce the parathyroid
hormone which plays an important role in regulating calcium and
phosphate ions in blood. These two ions are important in nerve and muscle
function, and in maintaining bone structure. Vitamin
D is important to the parathyroid glands because it promotes
retention of calcium and phosphate. Without vitamin D bones cannot develop and
they become soft and bend. This is the disease called rickets.
glands look like caps sitting on top of each kidney. Each adrenal is
composed of two distinct regions: an outer area called the adrenal
cortex, and an inner part called the adrenal
The adrenal cortex produces hormones that belong to a
group of chemical compounds known as corticosteroids,
corticoids, or just steroids.
The adrenal cortex makes many different steroids. The exact number is not known,
but it is believed to be over 30. The adrenal cortex has three layers, and each
layer produces different corticosteroids. The steroids corresponding to the
three layers are: the mineralocorticoid
(outer layer), glucocorticoids
(middle layer) and the androgenic
steroids (inner layer).
Aldosterone is the main
mineralocorticoid. It functions to cause the kidneys to reabsorption sodium and
excrete potassium. This helps to keep these two ions in balance. Hydrocortisone is the principle
glucocorticoid. Hydrocortisone help regulate the metabolism of carbohydrates,
proteins and fats. It also helps us cope with stress. Glucocorticoids cause a
rapid destruction of certain white blood cells, thereby lowering our resistance
to disease. Because they depress the immune system, glucocorticoids are used to
treat many autoimmune diseases. The production of glucocorticoids is under the
control of the adrenocorticotropic
hormone (ACTH). ACTH is produced by action of the pituitary gland.
The third group of steroids is the androgenic
steroids. These hormones are called androgens
and are male sex hormones. Testosterone
is the main androgen. While the adrenals of males and females produce near equal
amounts of androgens, males have an additional supply of androgens produced by
If the adrenal cortex produces insufficient amounts
of glucocorticoids and mineralocorticoids the result is called Addison's
Disease. The symptoms of
The adrenal medulla produces epinephrine
often called adrenalin
Both of these hormones are involved in the stress reaction called the "fight
or flight response." When confronted with danger, these two
hormones prepare our body to fight or to run. These hormones constrict the blood
vessels of the kidneys and digestive system, dilate blood vessels in the heart
and brain, raise blood pressure, and increase respiration. They constrict the
blood vessels of the skin so that we will lose less blood should we be bitten,
cut or shot. They rapidly convert glycogen to glucose, so that we might have
extra energy. And these hormones cause more neurotransmitters to be available to
our nervous system, so that our nerves can activate more muscle cells making us
faster and stronger. All of these changes prepare us to respond to danger.
lies between the kidneys. Cells known as the islets
of Langerhans are scattered throughout the pancreas. The islets of
Langerhans have two types of cells: alpha
cells which produce a hormone called glucagon, and the beta cells which produce a hormone called insulin.
Insulin is the hormone which escorts glucose across the cell membrane. Without
insulin, glucose cannot enter the cell and, therefore, cannot be used to produce
energy. Glucagon functions to cause the liver to convert more glycogen to
glucose, thereby, raising the blood sugar level.
If the Islets of Langerhans stop or lessen their
production of insulin, the result is diabetes
mellitus. The symptoms of diabetes include: loss of weight,
excessive thirst, increase in urination, itching in the skin, and fatigue.
Because glucose cannot enter cells, the blood sugar level is high. This high
blood sugar level causes sugar to be excreted in urine. High volumes of water
are needed to remove the sugar from the kidneys. Since water is used for this
purpose, thirst occurs to replace this lost water.
Since glucose is not available for cells to produce
energy, protein is used instead. This produces weight-loss, as the protein is no
longer available to form protoplasm. When cells attempt to use fat to produce
energy, the fat is incompletely burned and forms ketone
bodies. Ketone bodies are highly toxic and damage many parts of the
body. They may also be at least partially responsible for diabetic
There are many causes for diabetes. Two common types
are juvenile diabetes
and adult-onset diabetes.
In juvenile diabetes, because of genetics, it is suspected that when the child
contracts a specific virus, the thymus gland makes a white blood cell to eat the
virus. However, this particular white blood cell thinks that beta cells do not
belong to the body and eats them, too. The result is no insulin producing cells
at all. Such diabetics require an injection of insulin before each meal.
In adult-onset diabetes there are beta cells which
still produce insulin. However, because of factors, such as being over-weight,
for example, there is not enough insulin to serve these large fat cells.
Adult-onset diabetes may be controlled by diet, by drug treatments or insulin
injections. Insulin must be injected as digestion destroys insulin.
For many years diabetics injected insulin acquired
from animals. However, sometimes insulin from a certain animal would cease to
control their disease, and they would have to switch to insulin obtained from
another animal. Today human insulin can be made by genetic engineering, so that
such sensitization does not occur.
The opposite of diabetes is hypoglycemia.
Hypoglycemia occurs when the pancreas produces too much insulin. Since insulin
escorts glucose across the cell membrane, there is much sugar inside of cells
and a low blood sugar level. This low blood sugar is read by the hypothalamus
which causes a perception of hunger. Therefore, hypoglycemics appear to be
hungry almost all of the time. For this reason hypoglycemics often eat
excessively and gain weight. Hypoglycemics often feel faint, weak and develop
the "shakes." Most hypoglycemia can be controlled by diet--eating six
small protein meals each day.
are sex glands and consist of the ovaries
in females and the testes
in males. Testes produce sperm and male sex hormones, and ovaries produce female
The effect of sex hormones usually becomes noticeable
between the ages of 12--15 years of age when most boys and girls reach puberty.
Puberty is the biological event which brings the child into adolescence. It
occurs about one to two years earlier in girls than in boys. Puberty begins when
the pituitary gland releases the gonadotropic
hormone. The gonadotrophic hormone acts on the gonads causing them
to become functionally mature. When this occurs, the person will soon become
reproductively mature, and the gonads will greatly increase their production of
These sex hormones produce the secondary
sex characteristics for the sexes. These are things such as facial
hair in males, the appearance of breasts in females, pubic and axillary hair
(hair in the arm pits), lower voice for both sexes, and the other
characteristics which describe men and women.
Three different groups of hormones are produced by
the various organs of the female reproductive system. These are called the estrogenic
hormones (commonly called estrogen).
The first group, composed primarily of the hormone beta-estradiol is responsible for
maintaining the uterine environment, and it also effects behavior. The second
group, composed primarily of progesterone,
makes the uterus favorable to the reception of a developing embryo. The third, chorionic
gonadotrophin, prevents ovulation during pregnancy.
The male sex hormones are called androgens.
The main androgen is the steroid hormone known as testosterone.
Testosterone causes males to have larger muscle mass, and to be more aggressive
The pineal body (gland), attached to the lower
surface of the brain, is sometimes considered an endocrine gland. The pineal
gland secretes two hormones: serotonin
Serotonin functions as a neurotransmitter, and has been proven to be involved in
some depression. The pineal gland is stimulated to produce serotonin by
sunlight. The lack of sunlight in winter can result in a type depression called Seasonal
Affective Disorder or SAD. SAD can usually be treated with
fluorescent lights, or with antidepressant drugs such as Prozac. Melatonin may
be a hormone which triggers sleep. Melatonin may also be useful to correct
"jet lag," as it can be used to alter our "biological