ells. The result is the production an egg that ruptures from the ovary and passes into the oviduct. This process of the egg rupturing through the ovary wall and moving into the oviduct is called ovulation. Fertilization occurs in the oviduct if the egg and sperm unite. All the activities of the human female reproductive system are part of a cycle. Once the egg has been released, the remaining part of the follicle develops into a structure called the corpus luteum. The corpus luteum secretes the steroid hormone, progesterone. Progesterone causes changes to occur in the lining of the uterus, which prepare it for receiving a fertilized egg. The series of changes in the female reproductive system that include producing an egg and preparing the uterus for receiving it is known as the menstrual cycle.Menstrual CycleMenstrual cycles vary from between 15 and 31 days. The first day of the cycle is the first day of blood flow (day 0) known as menstruation. During menstruation the uterine lining is broken down and shed as menstrual flow. FSH and LH are secreted on day 0, beginning both the menstrual cycle and the ovarian cycle. Both FSH and LH stimulate the maturation of a single follicle in one of the ovaries and the secretion of estrogen. Rising levels of estrogen in the blood trigger secretion of LH, which stimulates follicle maturation and ovulation (day 14, or midcycle). LH stimulates the remaining follicle cells to form the corpus luteum, which produces both estrogen and progesterone.Estrogen and progesterone stimulate the development of the endometrium and preparation of the uterine inner lining for implantation of a zygote. If pregnancy does not occur, the drop in FSH and LH cause the corpus luteum to disintegrate. The drop in hormones also causes the sloughing off of the inner lining of the uterus by a series of muscle contractions of the uterus.Human DevelopmentFertilization, the fusion of the sperm and egg, usually occurs i...
