The endocrine system consists of glands or parts of glands which produce hormones that are released and distributed in the human body by means of the bloodstream. The major organs of the endocrine system are the hypothalamus, the pituitary gland, the thyroid gland, the parathyroid glands, the islets of the pancreas, the adrenal glands, the testes, and the ovaries.

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 that control a number of essential functions in the body, including growth and development.