Hormones are chemicals that are secreted in small amounts in one part of the body (endocrine gland) and then they travel through the bloodstream to control the activity of some other part of the body (target cell). The glands that produce hormones are principally controlled by the brain. Hormones speed up or slow down or alter the activity of those organs. There are more than 50 different hormones secreted in the human body. Some of the commonly known hormones are: insulin, thyroxine, growth hormone, etc.