Hormone
An example of positive feedback is the hormone that causes childbirth (when babies are born.) The hormone that causes this is oxytocin. This hormone is made by the pituitary gland. When the baby starts coming out, it stretches the muscle in the cervix (the bottom of the uterus). Nerves in the cervix send a message to the pituitary. This message makes the pituitary release more oxytocin. The oxytocin then causes the muscles of the uterus to contract, or squeeze. This causes more stretching in the cervix. This stretching then tells the pituitary to make even more oxytocin. So levels of oxytocin keep rising until the squeezing or contractions of the uterus force the baby out.