A hormone is not an organ. Hormones are chemical substances that are produced in the endocrine glands in the body. Hormones act as special messengers by controlling almost all bodily functions such as hunger, reproduction, emotions and mood. Examples of hormones and their major function are insulin (metabolic hormone), estrogen (sex hormone), adrenalin (stress hormone), ghrelin (hunger hormone), leptin (satiety hormone), melatonin (sleep hormone), testosterone (sex hormone) and thyroid (growth hormone).
