Overview of the Endocrine SystemHelp maintain the internal environment of the body within normal rangesDuctless glands that secrete hormone into the circulationHormones regulate slow physiological processThree groupsOrgans that contain only endocrine cells, e.g. pituitary gland, thyroid gland, parathyroid gland, adrenal glandOrgans that contain a large proportion of endocrine cells but also function in another organ system, e.g. pancreas, thymus, hypothalamusOrgans that contain some endocrine cells, e.g. heart, kidney, digestive tract