The endocrine system is a highly complex and diverse set of components present throughout the body of multi-cellular organisms. These are characterized by their role in the regulation of biological processes and behaviour by hormones. Hormones are specific chemical substances which travel throughout the body via the bloodstream, and are released into the bloodstream in response to specific events. Hormones come into contact with specialized receptors on or within cells, triggering events within these ‘target’ cells. This concept of chemical ‘signalling’ is associated with a wide array of biological processes.

Hormones are produced in endocrine glands, and there are several distinctive secretory organs specializing in the production and release of specific hormones. These are the hypothalamus, the pituitary gland, thyroid gland, pancreas, adrenal glands, pineal gland, ovaries, testes and the parathyroid gland. Smaller endocrine glands are also present throughout the body.