English: An important negative feedback mechanism in human beings is the ability to maintain body temperature. When the body temperature is too high or too low, the blood vessels will change size accordingly to bring the body’s temperature back to normal. In this diagram, the tube-shaped objects represent blood vessels and the red and blue objects represent thermometers. The middle blood vessel is sized for a blood vessel at normal body temperature. When the body temperature increases above normal temperature, a signal is sent to the hypothalamus of the brain which then sends an impulse into the body that indicates for the blood vessels to expand. When the blood vessels expand, heat is released out of the body and the body’s temperature lowers back to normal. This allows the blood vessels return to normal size. Similarly, when the body temperature decreases below normal temperature, a signal is sent to the hypothalamus of the brain which then sends an impulse into the body that indicates for the blood vessels to constrict. When the blood vessels constrict, heat is kept within the blood vessels, so less heat is lost to the environment through the skin and the body temperature can increase back to normal temperature and the blood vessels can expand back to their normal size.