What is the endocrine system?
The endocrine system is a collection of
glands that produce hormones, which regulate the body's growth,
metabolism, and sexual development and function. The hormones
are released into the bloodstream and transported to other
tissues and organs throughout the body.
The endocrine system is made up of three parts:
- Endocrine glands
- Hormones produced by the endocrine glands
- Tissues in the body
that respond to the hormones
released by the endocrine glands
Endocrine glands are specialized organs that produce, store,
and secrete (release) chemical messengers into the blood stream. These
chemical messengers are called hormones. The endocrine system includes
the following glands: pituitary, thyroid, parathyroid, adrenal, ovary,
testes, part of the pancreas, and, during pregnancy, the placenta.
The endocrine glands release more than 20 different hormones that influence
the functions of all of the body's tissues and organ systems.
Hormones, as the chemical messengers of the body, transfer information
and instructions from one part of the body to
another. Hormones regulate
- Growth and development
- Responses to surroundings, stress, and injury
and body energy levels
- Sexual function and reproductive
- Function of tissues in various organs
Hormones circulate throughout the bloodstream, but each kind
of hormone affects only certain cells, known as target cells.
When the hormone reaches its target cell, it locks onto specific receptors
on the cell. These hormone-receptor combinations then transmit chemical instructions
to the inner workings of the cell. This causes various changes within the
cell that affects the cell’s functioning.
Connection Between the Nervous System and the Endocrine System
The endocrine system is directly connected to the nervous system
through the hypothalamus. The hypothalamus is part of the brain that
lies just above the pituitary gland. Nerve cells located in the hypothalamus
control the pituitary gland by producing chemicals that either speed
up or slow down the release of hormones from the pituitary gland. The
hypothalamus directly controls the pituitary gland, which in turn controls
the functions of many of the other glands in the body.
How the Body Gives Feedback to the Endocrine System
To function properly, the body requires that hormone levels are not too high
or too low. For example, if growth hormone levels are too low, a child may
not grow and will be abnormally short. If growth hormone levels are too high,
a child may develop acromegaly, which typically involves overgrowth of bone
and internal organs like the heart and liver.
Too much or too little hormone can be harmful to the body. To prevent this,
the body has a feedback mechanism to regulate the levels of hormones in the
blood and tissues. This feedback mechanism works something like a home thermostat
that regulates heat. When the temperature in a house falls, the thermostat
responds by switching on the furnace. When the temperature is too warm, the
thermostat switches the furnace off.
The feedback mechanism can be fairly simple, or very complicated and involve
several glands. For example:
- Insulin controls the level of sugar
in the blood—when the blood
sugar goes up, the pancreas produces
more insulin, which lets more
sugar go into the cells. When the level of sugar in the blood drops,
releases less insulin, until
the sugar goes back up.
- The hypothalamus
secretes Thyrotropin Releasing
Hormone (TRH), which causes the pituitary gland to release
Thyroid Stimulating Hormone
(TSH). This then causes the thyroid gland to secrete thyroid
hormone, which regulates
the way the body uses energy. When there is enough thyroid hormone
in the blood, the body "feeds back" this information to the hypothalamus.
The hypothalamus decreases the secretion of TRH, which then causes
a decrease in secretion of TSH from the pituitary gland.
Learn More About the Endocrine Glands
To learn more about the endocrine glands and conditions due to problems with
hormones, select from the following list: