2.   What is a hormone?

A hormone is a chemical produced and secreted by endocrine (ductless) glands that travels through the bloodstream and controls and regulates the activity of another organs or groups of cells - its target organ. For instance, growth hormone released by the pituitary body controls the growth of long bones in the body.

The hormones perform three basic functions:

• hormones enable and promote physical, sexual and mental development;
  
  
• hormones enable and promote the adjustment of performance level; the ability of organs and organ systems to modify their activity to meet the demands made upon them is lost in the absence of certain hormones;
  
  
• hormones are necessary to keep certain physiological parameters constant (e.g., osmotic pressure and the blood glucose level). These hormones have a homeostatic function.
  

For more detiled information on hormones, go the "endocrine primer" section.