Ever dozed through chemistry class and wondered what chemistry
had to do with you? A lot! Your body produces its own chemicals and
uses them to control certain functions, and the main system that
coordinates these chemicals is called the
endocrine system
.
What Is the Endocrine System?
Although we rarely think about the endocrine system, it
influences almost every cell, organ, and function of our bodies.
The endocrine system is instrumental in regulating mood, growth and
development, tissue function, metabolism, and sexual function and
reproductive processes.
In general, the endocrine system is in charge of body processes
that happen slowly, such as cell growth. Faster processes like
breathing and body movement are controlled by the nervous system.
But even though the nervous system and endocrine system are
separate systems, they often work together to help the body
function properly.
The foundations of the endocrine system are the hormones and
glands. As the body's chemical messengers,
hormones
(pronounced:
hor
-moanz) transfer information and instructions from one set of cells
to another. Many different hormones move through the bloodstream,
but each type of hormone is designed to affect only certain
cells.
A
gland
is a group of cells that produces and secretes, or gives off,
chemicals. A gland selects and removes materials from the blood,
processes them, and secretes the finished chemical product for use
somewhere in the body. Some types of glands release their
secretions in specific areas. For instance,
exocrine
(pronounced:
ek
-suh-krin)
glands
, such as the sweat and salivary glands, release secretions in the
skin or inside the mouth.
Endocrine glands
, on the other hand, release more than 20 major hormones directly
into the bloodstream where they can be transported to cells in
other parts of the body.
The major glands that make up the human endocrine system include
the:
- hypothalamus
- pituitary gland
- thyroid
- parathyroids
- adrenal glands
- pineal body
- reproductive glands (which include the ovaries and
testes)
Hypothalamus
The
hypothalamus
(pronounced: hi-po-
tha
-luh-mus), a collection of specialized cells that is located in the
lower central part of the brain, is the main link between the
endocrine and nervous systems. Nerve cells in the hypothalamus
control the pituitary gland by producing chemicals that either
stimulate or suppress hormone secretions from the pituitary.
Pituitary
Although it is no bigger than a pea, the
pituitary
(pronounced: puh-
too
-uh-ter-ee)
gland
, located at the base of the brain just beneath the hypothalamus,
is considered the most important part of the endocrine system.
It's often called the "master gland" because it makes
hormones that control several other endocrine glands. The
production and secretion of pituitary hormones can be influenced by
factors such as emotions and changes in the seasons. To accomplish
this, the hypothalamus provides information sensed by the brain
(such as environmental temperature, light exposure patterns, and
feelings) to the pituitary.
The tiny pituitary is divided into two parts: the anterior lobe
and the posterior lobe. The
anterior lobe
regulates the activity of the thyroid, adrenals, and reproductive
glands. The anterior lobe produces hormones such as:
-
growth hormone
, which stimulates the growth of bone and other body tissues and
plays a role in the body's handling of nutrients and
minerals
-
prolactin
(pronounced: pro-
lak
-tin), which activates milk production in women who are
breastfeeding
-
thyrotropin
(pronounced: thy-ruh-
tro
-pin), which stimulates the thyroid gland to produce thyroid
hormones
-
corticotropin
(pronounced: kor-tih-ko-
tro
-pin), which stimulates the adrenal gland to produce certain
hormones
The pituitary also secretes
endorphins
(pronounced: en-
dor
-fins), chemicals that act on the nervous system and reduce
feelings of pain. In addition, the pituitary secretes hormones that
signal the reproductive organs to make sex hormones. The pituitary
gland also controls ovulation and the menstrual cycle in women.
The
posterior lobe
of the pituitary releases
antidiuretic
(pronounced: an-ty-dy-uh-
reh
-tik)
hormone
, which helps control the balance of water in the body. The
posterior lobe also produces
oxytocin
(pronounced: ahk-see-
toe
-sin), which triggers the contractions of the uterus in a woman
having a baby.
Thyroid
The
thyroid
(pronounced:
thy
-royd), located in the front part of the lower neck, is shaped like
a bow tie or butterfly and produces the thyroid hormones
thyroxine
(pronounced: thy-
rahk
-sin) and
triiodothyronine
(pronounced: try-eye-oh-doe-
thy
-ruh-neen). These hormones control the rate at which cells burn
fuels from food to produce energy. The production and release of
thyroid hormones is controlled by
thyrotropin
(pronounced: thigh-ruh-
tro
-pin), which is secreted by the pituitary gland. The more thyroid
hormone there is in a person's bloodstream, the faster chemical
reactions occur in the body.
Why are thyroid hormones so important? There are several reasons
- for example, they help kids' and teens' bones grow and
develop, and they also play a role in the development of the brain
and nervous system in kids.
Parathyroids
Attached to the thyroid are four tiny glands that function
together called the
parathyroids
(pronounced: par-uh-
thy
-roydz). They release
parathyroid hormone
, which regulates the level of calcium in the blood with the help
of
calcitonin
(pronounced: kal-suh-
toe
-nin), which is produced in the thyroid.
Adrenal Glands
The body also has two triangular
adrenal
(pronounced: uh-
dree
-nul)
glands
, one on top of each kidney. The adrenal glands have two parts,
each of which produces a set of hormones and has a different
function. The outer part, the
adrenal cortex
, produces hormones called
corticosteroids
(pronounced: kor-tih-ko-
ster
-oydz) that influence or regulate salt and water balance in the
body, the body's response to stress, metabolism, the immune
system, and sexual development and function. The inner part, the
adrenal medulla
(pronounced: muh-
duh
-luh), produces
catecholamines
(pronounced: kah-tuh-
ko
-luh-meenz), such as
epinephrine
(pronounced: eh-puh-
neh
-frun). Also called adrenaline, epinephrine increases blood
pressure and heart rate when the body experiences stress.
Pineal
The
pineal
(pronounced: pih-
nee
-ul)
body
, also called the pineal gland, is located in the middle of the
brain. It secretes
melatonin
(pronounced: meh-luh-
toe
-nin), a hormone that may help regulate when you sleep at night and
when you wake in the morning.
Reproductive Glands
The
gonads
are the main source of sex hormones. Most people don't realize
it, but both guys and girls have gonads. In guys the male gonads,
or
testes
(pronounced:
tes
-teez), are located in the scrotum. They secrete hormones called
androgens
(pronounced:
an
-druh-junz), the most important of which is
testosterone
(pronounced: teh-
stass
-tuh-rone). These hormones tell a guy's body when it's time
to make the changes associated with
puberty
, like penis and height growth, deepening voice, and growth in
facial and pubic hair. Working with hormones from the pituitary
gland, testosterone also tells a guy's body when it's time
to produce sperm in the testes.
A girl's gonads, the
ovaries
(pronounced:
oh
-vuh-reez), are located in her pelvis. They produce eggs and
secrete the female hormones
estrogen
(pronounced:
es
-truh-jen) and
progesterone
(pronounced: pro-
jes
-tuh-rone). Estrogen is involved when a girl begins to go through
puberty. During puberty, a girl will experience breast growth, will
begin to accumulate body fat around the hips and thighs, and will
have a growth spurt. Estrogen and progesterone are also involved in
the regulation of a girl's menstrual cycle. These hormones also
play a role in pregnancy.
Although the endocrine glands are the body's main hormone
producers, some other organs not in the endocrine system - such as
the brain, heart, lungs, kidneys, liver, and skin - also produce
and release hormones. The
pancreas
(pronounced:
pan
-kree-us) is also part of the body's hormone-secreting system,
even though it is also associated with the digestive system because
it produces and secretes digestive enzymes. The
pancreas
produces (in addition to others) two important hormones,
insulin
(pronounced:
in
-suh-lin) and
glucagon
(pronounced:
gloo
-kuh-gawn). They work together to maintain a steady level of
glucose, or sugar, in the blood and to keep the body supplied with
fuel to produce and maintain stores of energy.
What Does the Endocrine System Do?
Once a hormone is secreted, it travels from the endocrine gland
that produced it through the bloodstream to the cells designed to
receive its message. These cells are called target cells. Along the
way to the target cells, special proteins bind to some of the
hormones. These proteins act as carriers that control the amount of
hormone that is available for the cells to use. The target cells
have receptors that latch onto only specific hormones, and each
hormone has its own receptor, so that each hormone will communicate
only with specific target cells that have receptors for that
hormone. When the hormone reaches its target cell, it locks onto
the cell's specific receptors and these hormone-receptor
combinations transmit chemical instructions to the inner workings
of the cell.
When hormone levels reach a certain normal amount, the endocrine
system helps the body to keep that level of hormone in the blood.
For example, if the thyroid gland has secreted the right amount of
thyroid hormones into the blood, the pituitary gland senses the
normal levels of thyroid hormone in the bloodstream. Then the
pituitary gland adjusts its release of thyrotropin, the hormone
that stimulates the thyroid gland to produce thyroid hormones.
Another example of this process is parathyroid hormone.
Parathyroid hormone increases the level of calcium in the blood.
When the blood calcium level rises, the parathyroid glands sense
the change and reduce their secretion of parathyroid hormone. This
turnoff process is called a negative feedback system.
Things That Can Go Wrong With the Endocrine System
Too much or too little of any hormone can be harmful to your
body. For example, if the pituitary gland produces too much growth
hormone, a teen may grow excessively tall. If it produces too
little, a teen may be unusually short. Doctors can often treat
problems with the endocrine system by controlling the production of
hormones or replacing certain hormones with medication. Some
endocrine problems that affect teens include:
Adrenal insufficiency.
This condition occurs when the adrenal glands don't produce
enough corticosteroids. The symptoms of adrenal insufficiency may
include weakness, fatigue, abdominal pain, nausea, dehydration, and
skin changes. Doctors treat adrenal insufficiency with medications
to replace corticosteroid hormones.
Type 1
diabetes
.
When the pancreas fails to produce enough insulin, type 1 diabetes
(pronounced: dy-uh-
be
-teez and previously known as juvenile diabetes) occurs. In kids
and teens, type 1 diabetes is usually an autoimmune disorder, which
means that some parts of the body's immune system attack and
destroy the cells of the pancreas that produce insulin. To control
their blood sugar levels and reduce the risk of developing diabetes
problems, kids and teens with this condition need regular
injections of insulin.
Type 2 diabetes.
Unlike type 1 diabetes, in which the body can't produce normal
amounts of insulin, in type 2 diabetes the body can't respond
to insulin normally. Kids and teens with the condition tend to be
overweight. Some kids and teens can control their blood sugar level
with dietary changes, exercise, and oral medications, but many will
need to take insulin injections like people with type 1
diabetes.
Growth hormone problems.
Too much growth hormone in kids and teens who are still growing
will make their bones and other body parts grow excessively. This
rare condition (sometimes called gigantism) is usually caused by a
pituitary tumor and can be treated by removing the tumor. The
opposite can happen when a kid or teen has a pituitary glad that
doesn't produce enough growth hormone. Doctors may treat these
growth problems with medication.
Hyperthyroidism
.
Hyperthyroidism (pronounced: hi-per-
thy
-roy-dih-zum) is a condition in which the levels of thyroid
hormones in the blood are very high. In kids and teens, the
condition is usually caused by Graves' disease, an immune
system problem that causes the thyroid gland to become very active.
Doctors may treat hyperthyroidism with medications, surgery, or
radiation treatments.
Hypothyroidism
. Hypothyroidism (pronounced: hi-po-
thy
-roy-dih-zum) is a condition in which the levels of thyroid
hormones in the blood are very low. Thyroid hormone deficiency
slows body processes and may lead to fatigue, a slow heart rate,
dry skin, weight gain, constipation. Kids and teens with this
condition may also grow more slowly and reach puberty at a later
age. Hashimoto's thyroiditis is an immune system problem that
often causes problems with the thyroid and blocks the production of
thyroid hormone. Doctors often treat this problem with
medication.
Precocious puberty.
If the pituitary glands release hormones that stimulate the gonads
to produce sex hormones too early, some kids may begin to go
through puberty at a very young age. This condition is called
precocious puberty. Kids and teens who are affected by precocious
puberty can be treated with medication that will help them develop
at a normal rate.
Updated and reviewed by:
Steven Dowshen, MD
Date reviewed: July 2007
Note: All information is for educational purposes only. For specific medical advice,
diagnoses, and treatment, consult your doctor.
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