Definition: Hormones are produced in the endocrine glands, where they are excreted into the bloodstream. They perform a wide range of roles in the various organs including the regulation of metabolic pathways and the regulation of membrane transport processes.

Hormones may be grouped into three structural classes:

 The steroids are one class of such hormones. They perform a variety of functions, but they are all made from cholesterol.
 Simple amines or amino acids.
 peptides or proteins.

See also

 endocrine system

• endocrine glands

 endocrine pathology