1. A substance that is manufactured and secreted in very small quantities into the bloodstream by an endocrine gland or a specialized nerve cell (see neurohormone) and regulates the growth or functioning of a specific tissue or organ in a distant part of the body. For example, the hormone insulin controls the rate and manner in which glucose is used by the body. Other hormones include the sex hormones, corticosteroids, adrenaline, thyroxine, and growth hormone.