These are both hormones, or chemical messengers that travel in the bloodstream to a target organ, where an effect will occur. They are part of the endocrine system. Epinephrine, also called adrenaline, is released from the adrenal glands, located on top of each kidney. It is both a hormone and a neurotransmitter. In emergency situations, it helps with the fight or flight response of the sympathetic nervous system. Its release triggers increased heart rate, the muscles will tense, more air moves into the lungs and blood flows more rapidly. This will ensure that a person has a chance to fight back or flee from an emergency. The major trigger of adrenaline is usually some type of stress. This could be a threat, excitement, noise, etc. Norepinephrine, or noradrenaline is a hormone and a neurotransmitter. When it is released from sympathetic neurons, it will increase the rate of heart contractions. As a stress hormone, it affects parts of the brain where attention and responses are controlled. It also contributes to the fight or flight response by increasing heart rate, releasing glucose for energy and increasing blood flow to where its needed. These are necessary chemicals that enable the body to cope because of the activation of the flight or fight response.