The process of hormone signal transduction begins with endocrine cells or glands producing and secreting hormones into the circulatory system. These hormones travel through the bloodstream to reach target organs or cells far from their site of origin. Hormones bind to specific receptors on the surface of target cells or cross the cell membrane to bind with intracellular receptors, triggering a series of signal transduction events. These events typically involve the generation of second messengers such as cyclic adenosine monophosphate (cAMP) and calcium ions, as well as the activation of protein kinases, ultimately leading to changes in cell function and the production of physiological effects.