The endocrine system1 is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems.
In humans, the major are the , , , , and , and the (male) and (female) . The , , and also function as endocrine glands, among other functions. (The hypothalamus and pituitary glands are organs of the . One of the most important functions of the hypothalamus—it is located in the adjacent to the pituitary gland—is to link the endocrine system to the via the pituitary gland.) Other organs, such as the , also have roles within the endocrine system by secreting certain hormones. The study of the endocrine system and its disorders is known as . The secretes , the secretes , the secretes , the testis secretes , and the secrete and .