The adrenal glands, which are located at the top of each kidney regulate the fight or flight response. They secrete the hormones adrenaline, noradrenaline and cortisol. During stressful or emergency situations, a stress response is activated. This results in the secretion of adrenaline into the bloodstream. It affects the muscles aiding in the ability to have the strength to fight back, or to flee. It may affect mood or behavior--increased aggression in the fighting response, or withdrawal or running away, for the flight response. During this event, digestion system slows down as does the reproductive system. Prolonged stress can negatively affect the immune system and the circulatory system. Noradrenaline increases heart rate, triggering release of glucose from energy storage to obtain the energy needed during fight or flight response. It affects how much oxygen the brain receives and increases blood pressure. Cortisol, a steroid hormone, is released by the zona fasciculata part of the adrenals. It is released when there is stress and its function is to increase blood sugar, suppress the immune system and aid in the release of energy stores in the body. It also decreases bone formation.The hypothalmus part of the brain triggers the release of cortisol by the adrenals. Cortisol activates anti-stress and anti-inflammation pathways in the body.