Stress is the body’s method of reacting to a condition such as a threat, challenge or physical and psychological barrier. Stimuli that alter an organism’s environment are responded to by multiple systems in the body. The autonomic nervous system and hypothalamic-pituitary-adrenal (HPA) axis are two major systems that respond to stress

stress can alter memory functions, reward, immune function, metabolism and susceptibility to diseases. Definitions of stress differ. One system suggests there are five types of stress labeled “acute time-limited stressors”, “stressful event sequences”, “chronic stressors”, and “distant stressors”.