The endocrine system uses hormones released into the bloodstream to stimulate the metabolic activities of the cells. 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 endocrine glands in 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.