Next to the nervous system the endocrine system is the system that controls the body.  However, the endocrine system uses hormones to stimulate the metabolic activities of the cells.  These hormones are released into the blood stream.  Tissue response to hormones usually occur after a lag time of seconds or days.  Once started the responses tend to be much more prolonged  than those that are induced by the nervous system.

     The organs of the endocrine system are small and unimpressive.  The endocrine glands of the body include the pituitary, thyroid, parathyroid, adrenal, pineal, and thymus.

     Hormones are chemical compounds that regulate metabolic function of cells in the body.  There are two types of hormones: amino acid-based hormones and steroids.  Most hormones are amino acid-based.  Steroid hormones are synthesized from cholesterol.  Only the gonadal hormones and adrenocortical hormones are steroids.