Hormones are chemical substances that are created by specific glands at certain locations in the body, then dumped into the blood stream where they influence and cause specific reactions from cells in other parts of the body. They do this as a result of hormone specific receptors that are located either on the cell membrane, or within the cell's cytoplasm itself. A good example of a short loop response is epinephrine, or adrenaline, that is manufactured by the adrenal glands. This hormone produces the "fight or flight" response, where the heart rate accelerates, the respiratory rate quickens, the pupils dilate, and the body generally prepares to fight the fight of its life, or run the race of its life. A long loop feedback would be the cessation of production of adrenalin, causing the vital signs to slow down and return to normal. Hormones perform vital functions for the body, without which, life would not occur.