Hormones are chemical messengers secreted by glands.  They are responsible for specific regulatory effects on target cells, within organs.  The target cell is distinguished by specific protein receptors within its plasma membrane.  Hormones arouse target cells by increasing or decreasing the normal homeostatic level of activity. For this to happen one of the following changes must occur; stimulation of mitosis, activation of enzymes, changes in the permeability of the plasma membrane, or the production of proteins within the cell.

  Hormone functions can be categorized into the areas of, growth and development, reproduction, mobilization of bodily defenses, water and nutrient balance, maintenance of electrolyte, and the regulation of cellular metabolism.

A large amount of hormones can be identified as amino acid based molecules.

There are over 50 hormones in the human body, and they can be grouped together by their chemical structure. For example Steroids are produced from cholesterol,. and Peptides are chains of amino acids