There are other disturbances that occur in the internal environment that can act as a stimulus to a feedback mechanism, one of which is the rise or fall of our body temperature. In our body, when our body temperature decreases, we experience shivering as our brain sends a message to the muscles to shiver since shivering produces heat. Hence, our body temperature would be regulated since shivering would cause our body temperature to rise up. In the same way, when our body temperature increases, our brain would send a signal to the sweat glands to produce sweat in order to cool down our body and regulate the temperature. Another example would be the menstrual cycle. The menstruation cycle happens when ovulation occurs, which is after the release of follicle-stimulating hormone. The process starts when the estrogen is released, which will send a signal to the brain to release gonadotrophin-releasing hormone and luteinizing hormone, which is released by the pituitary gland. These hormones influence the ovaries to release more estrogen until the levels of these hormones reach high enough to signal the release of follicle-stimulating hormone - the start of ovulation.