This document discusses endocrinology and the endocrine system. It describes how endocrinology deals with hormones, their synthesis, secretion and action. Hormones are chemical messengers that coordinate activities between different cells and allow specialized tissues to function in an integrated manner through the nervous and endocrine systems. The endocrine system relies on hormones being released into circulation to act at distant sites, unlike the nervous system which uses electrochemical signals along neuronal pathways. Endocrine disorders can involve hormonal excess or deficiency and are classified accordingly.