The endocrine system is a network of glands and cells that secrete hormones directly into the bloodstream to regulate distant target organs and tissues. Major glands include the pituitary, thyroid, adrenals, pancreas, and gonads. Hormones act as chemical messengers to control vital processes such as metabolism, growth and development, mood, reproduction, and homeostasis. It works in a closely integrated manner with the nervous system to coordinate bodily functions.