Hormones are biologically active substances of an organic nature, produced in specialized cells of endocrine glands (endocrine glands) that enter the bloodstream, bind to receptors of target cells and have a regulatory effect on metabolism and physiological functions. Types of classifications of hormones. Modern science knows more than 100 hormones, their chemical nature and mechanism of action have been studied in sufficient detail. But, despite this, the general nomenclature of these biologically active substances has not yet appeared.