1.  What is the endocrine system?

Humans have two systems of internal communication: the nervous system and the endocrine system. The endocrine system controls the delivery of messages through the release of chemicals known as hormones. Hormones are secreted directly into the blood by endocrine glands.

Endocrine glands are found throughout the body and are responsible for releasing more than 50 hormones. Endocrine glands include the pituitary, hypothalamus, thyroid and parathyroid, pancreas, adrenal, and the gonads (ovaries and testes). In pregnant women the placenta also functions as an endocrine gland becoming the principle site of steroid production during pregnancy. The hormones produced by endocrine glands may be either proteins or steroids such as the sex steroids: estrogen, progesterone and testosterone.

For more detailed information on the endocrine system, go to the "science and issues" section.

For a more graphical and animated illustration of the endocrine system, go the "endocrine primer" section.