Learn more about the endocrine system: http://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/biology-of-the-endocrine-system/endocrine-glands The endocrine system involves hormones, chemical messengers that affect various body functions. The hypothalamus, part of the brain, controls the pituitary gland, which itself releases hormones that control other organs in the endocrine system, such as the thyroid and adrenal glands. Growth hormone controls functions such as the body’s growth. Thyroid hormone controls the rate of the body’s metabolism (for example, its heart rate and how rapidly chemical reactions are processed. The pancreas produces insulin, which helps blood sugar enter cells; when there is too little insulin, diabetes develops. The adrenal glands, one on each kidney, make adrenaline (epinephrine), aldosterone, and cortisol, which help the body adapt to stress and maintain heart rate and blood pressure. The testes make testosterone, the male sex hormone, and sperm. The ovaries make estrogen, the female sex hormone, and contain eggs. About The Merck Manuals: First published in 1899 as a small reference book for physicians and pharmacists, The Merck Manual grew in size and scope to become one of the world’s most widely used comprehensive medical resources for professionals and consumers. As The Manual evolved, it continually expanded the reach and depth of its offerings to reflect the mission of providing the best medical information to a wide cross-section of users, including medical professionals and students, veterinarians and veterinary students, and consumers. • Merck Manual Consumer Version: http://www.MerckManuals.com/Home • Facebook for Consumers: http://www.Facebook.com/MerckManualHomeUS • Twitter for Consumers: http://www.Twitter.com/MerckManualHome