What are hormones?
Hormones are chemicals which are produced by endocrine glands and secreted into our blood stream. These are transported to various parts of our body by the circulatory system (along with blood) and are primarily responsible for regulating a number of physiological and behavioral functions. Some of the functions regulated by the hormones include growth and development, menstruation, hunger, sexual functions, etc. In the human body, we have a number of glands (including pituitary, thyroid, ovaries, testes, pancreas, hypothalamus, etc.) that together constitute the endocrine glands. In fact, there are over 50 known hormones secreted by our body. Slight changes in hormone content of our body can have strong effects. Many times we read reports of a sportsperson caught for being on hormones (for performance enhancement).
Hope this helps.