This article waslast modified on 10 July 2017.
Chemical produced and secreted by endocrine (ductless) glands that travels through the bloodstream and controls or regulates the activity of another organ or group of cells - its target organ. (For example, growth hormone released by the pituitary gland controls the growth of long bones of the body.) There are two main types of hormones - steroidal (e.g., oestrogen, testosterone, aldosterone, cortisol) and non-steroidal. Secretion of hormones is regulated by feedback mechanisms and neurotransmitters.