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Endocrine Disruption
Contact Us


WHAT IS THE ENDOCRINE SYSTEM?

Endocrine systems, also referred to as hormone systems, are found in all
mammals, birds, fish, and many other types of living organisms. They are made up
of:

 * Glands located throughout the body;
 * Hormones that are made by the glands and released into the bloodstream or the
   fluid surrounding cells; and
 * Receptors in various organs and tissues that recognize and respond to the
   hormones.

Learn more about endocrine systems:

 * Why are hormones important?
 * Where are endocrine glands located in the human body?
 * How can chemicals affect endocrine systems?

--------------------------------------------------------------------------------


WHY ARE HORMONES IMPORTANT?

Hormones act as chemical messengers that are released into the blood stream to
act on an organ in another part of the body. Although hormones reach all parts
of the body, only target cells with compatible receptors are equipped to
respond. Over 50 hormones have been identified in humans and other vertebrates.

Hormones control or regulate many biological processes and are often produced in
exceptionally low amounts within the body. Examples of such processes include:

 * blood sugar control (insulin);
 * differentiation, growth, and function of reproductive organs (testosterone
   (T) and estradiol); and
 * body growth and energy production (growth hormone and thyroid hormone).

Much like a lock and key, many hormones act by binding to receptors that are
produced within cells. When a hormone binds to a receptor, the receptor carries
out the hormone's instructions, either by altering the cell's existing proteins
or turning on genes that will build a new protein. The hormone-receptor complex
switches on or switches off specific biological processes in cells, tissues, and
organs.

Some examples of hormones include:

 * Estrogens are the group of hormones responsible for female sexual
   development. They are produced primarily by the ovaries and in small amounts
   by the adrenal glands.
 * Androgens are responsible for male sex characteristics. Testosterone, the sex
   hormone produced by the testicles, is an androgen.
 * The thyroid gland secretes two main hormones, thyroxine and triiodothyronine,
   into the bloodstream. These thyroid hormones stimulate all the cells in the
   body and control biological processes such as growth, reproduction,
   development, and metabolism.

The endocrine system, made up of all the body's different hormones, regulates
all biological processes in the body from conception through adulthood and into
old age, including the development of the brain and nervous system, the growth
and function of the reproductive system, as well as the metabolism and blood
sugar levels. The female ovaries, male testes, and pituitary, thyroid, and
adrenal glands are major constituents of the endocrine system.


WHERE ARE ENDOCRINE GLANDS LOCATED IN THE HUMAN BODY?



Hypothalamus - The hypothalamus links our endocrine and nervous systems
together. The hypothalamus drives the endocrine system.

Pituitary gland - The pituitary gland receives signals from the hypothalamus.
This gland has two lobes, the posterior and anterior lobes. The posterior lobe
secretes hormones that are made by the hypothalamus. The anterior lobe produces
its own hormones, several of which act on other endocrine glands.

Thyroid gland - The thyroid gland is critical to the healthy development and
maturation of vertebrates and regulates metabolism.

Adrenal glands - The adrenal gland is made up of two glands: the cortex and
medulla. These glands produce hormones in response to stress and regulate blood
pressure, glucose metabolism, and the body's salt and water balance.

Pancreas - The pancreas is responsible for producing glucagon and insulin. Both
hormones help regulate the concentration of glucose (sugar) in the blood.

Gonads - The male reproductive gonads, or testes, and female reproductive
gonads, or ovaries, produce steroids that affect growth and development and also
regulate reproductive cycles and behaviors. The major categories of gonadal
steroids are androgens, estrogens, and progestins, all of which are found in
both males and females but at different levels.


HOW CAN CHEMICALS AFFECT THE ENDOCRINE SYSTEM?

Scientific research on human epidemiology, laboratory animals, and fish and
wildlife suggests that environmental contaminants can disrupt the endocrine
system leading to adverse-health consequences. It is important to gain a better
understanding of what concentrations of chemicals found in the environment may
cause an adverse effect. Various types of scientific studies (epidemiology,
mammalian toxicology, and ecological toxicology) are necessary to resolve many
of the scientific questions and uncertainty surrounding the endocrine disruptor
issue. Many such studies are currently underway by government agencies,
industry, and academia.

Learn more with EDSP about concerns and examples of endocrine disruption.

 * Endocrine Disruption Home
 * Learn About Endocrine Disruption
 * Program Overview
 * Research
 * Regulatory Resources
 * Chemical Screening and Testing Progress

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Last updated on March 7, 2022