The endocrine system is a complex network of glands, hormones and receptors that all work together in the body to regulate and maintain homeostasis. The endocrine system controls many body functions, such as metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood. The endocrine system is composed of a range of different glands that produce and secrete hormones into the bloodstream. The most important endocrine glands are the hypothalamus, pituitary, thyroid, parathyroid, adrenal, and reproductive glands. Each gland has its own set of hormones, which are secreted into the bloodstream and travel to other parts of the body to regulate various body functions. The hypothalamus is the most important endocrine gland and is responsible for regulating many other endocrine glands. It produces hormones that stimulate the pituitary gland to produce other hormones. The pituitary gland then produces and secretes hormones that act on other endocrine glands, such as the thyroid, parathyroid, and adrenal glands, to regulate their activities. The thyroid gland is responsible for releasing hormones that control metabolism, growth and development, and tissue function. The parathyroid gland produces hormones that regulate calcium levels in the blood.