Hormones are chemical messengers produced by a gland and transported in the bloodstream throughout the body, transferring information and instructions between cells. Most of our hormones are synthesized and secreted by the endocrine system. Each gland of the endocrine system produces its own unique hormones and each of those hormones serves as a chemical messenger to deliver very specific information to specific cells or organs in the body.
Hormones have the ability to regulate growth, metabolism, reproduction, and behavior. The specific tissue acted on by each hormone is the target tissue. Once a hormone binds to a receptor on or in a target cell, it affects cell activities, regulating the manufacture of proteins, changing the permeability of the cell membrane, or affecting metabolic reactions.