The Female Menstrual Cycle There are 4 parts to the female menstrual cycle:
Part 1- Flow phase • Marks the beginning of the cycle • Characterized by the shedding of the endometrium. • This phase usually lasts about 4 days
Part 2- Follicular phase • Development of a follicle within the ovary • The follicle cells produce estrogen which promotes the thickening of the endometrium. Estrogen also triggers development of the secondary sexual characteristics. • Usually only one follicle matures during each cycle • Usually lasts about 10 days
Part 3- Ovulation • The oocyte bursts from follicle • The remaining follicle cells become the corpus luteum • This occurs on about day 14.
Part 4- Luteal phase • The development and maturation of corpus luteum occurs during this phase • The concentration of estrogen declines briefly because the follicle is gone • The corpus luteum begins secreting progesterone. Progesterone • maintains the endometrium • strengthens the uterus • inhibits further ovulation • prevents uterine contractions • If pregnancy does not occur, the concentration of progesterone declines which triggers uterine contractions and the endometrium is shed.