Hormone is a chemical substance produced in the body that controls and regulates the activity of certain cells or organs. Many hormones are secreted by specialized glands such as the thyroid gland. Hormones are essential for every activity of daily living, including the processes of digestion, metabolism, growth, reproduction, and mood control. Many hormones, such as the neurotransmitters, are active in more than one physical process. Examples of hormones include aldosterone, antidiuretic hormone(ADH), cortisol, erythropoietin, estrogen, human chorionic gonadotropin (hCG), parathormone, progesterone, and testosterone.