An important change during adolescence for a female, is the beginning of a monthly cycle to prepare the uterus to receive and nourish a possible fertilized egg. This monthly cycle is called the menstrual cycle. Ap- proximately every ____ days, an egg is released from one of the ______ and begins to travel down the ___________ _____. The _______ alternate the release of eggs. One month, the left _____ releases an egg, and the next month, the right _______ takes its turn. The release of an egg from an ovary is referred to as ____________. During this time, the ______ has been undergoing changes. The walls of the _______ fill with _________ and become thicker. If the egg that travels through the __________ ____ becomes fertilized by a ______ ______, then the egg will implant itself in the lining of the _________ and begin the process of devel- opment, which can lead to new life. If the egg isn't __________, it will break down and leave the body with the used _______ and tissue that had collected in the ________ wall. The blood and tissue leave the body through the ________ over an average ___ -day period of time. This is called ___________.