The endocrine system consists of glands, tissues, and individual cells that secrete molecular messengers, called hormones.
Hormones travel through the body by means of the blood vessels.
When a hormone is released to the bloodstream, it will eventually interact with a specific cell membrane or cytoplasmic receptor of one or more classes of target cells. Endocrine glands regulate body metabolism, reproductive function, blood electrolytes, growth, blood pressure, uterine contractions, skin pigmentation, water retention, and blood nutrient levels, as well as many other functions. There are usually feedback regulation mechanisms between hormones and their target cell products and even other hormones. Some endocrine glands, such as the pituitary and adrenal glands, are closely linked to the nervous system. The endocrine glands include the pituitary, adrenals, thyroid, parathyroids, pancreas, ovaries, testes, and thymus.