 The term "hormone" is sometimes extended to include chemicals produced by cells that affect the same cell (autocrine or intracrine signaling) or nearby cells (paracrine signalling).Hormones serve to communicate between organs and tissues for physiological regulation and behavioral activities such as digestion, metabolism, respiration, tissue function, sensory perception, sleep, excretion, lactation, stress induction, growth and development, movement, reproduction, and mood manipulation.Hormones affect distant cells by binding to specific receptor proteins in the target cell, resulting in a change in cell function.