The four main phases of the menstrual cycle are: Menstrual phase. Follicular phase. Ovulation phase. Luteal phase. Menstruation phase Menstruation is the passage of the thickened lining of the uterus (endometrium) out of the body through the vagina. Menstrual fluid contains blood, cells from the lining of the uterus (endometrial cells), and mucus. The average length of a period is from three days to a week. Follicular phase The follicular phase begins on the first day of the menstrual period and ends with ovulation. Driven by the hypothalamus, the pituitary gland secretes follicle-stimulating hormone (FSH). This hormone stimulates the ovaries to produce about 5 to 20 follicles (nodules or follicles), the seeds on the surface. Each follicle contains an immature egg. Usually, only one follicle matures into an egg, while the others die. This can happen around day 10 of a 28-day cycle. The growth of cysts stimulates the lining of the uterus to thicken in preparation for pregnancy. Ovulation phase Ovulation is the release of a mature egg from the surface of the ovary. This usually happens mid-cycle, about two weeks or so before menstruation begins. Within two days, ovulation is triggered by high LH levels. Eggs are carried into the fallopian tubes and toward the uterus in tiny hair-like ejections. The lifespan of a typical egg is only about 24 hours. Unless it encounters sperm during this time, it will die. The luteal phase During ovulation, the egg breaks out of the follicle, but the ruptured follicle remains on the surface of the ovary. Over the next two weeks or so, the follicle transforms into a structure known as the corpus luteum. This structure initiates the release of progesterone, along with a small amount of estrogen. The combination of these hormones will keep the lining of the uterus thickened, waiting for a fertilized egg to implant (implant). If the fertilized egg implants in the lining of the uterus, it produces the hormones needed to maintain the corpus luteum. If there is no pregnancy, the corpus luteum will wither and die, usually around day 22 of a 28-day cycle. A drop in progesterone levels causes the lining of the uterus to shed. This is called menstruation. Then the cycle repeats. (betterhealth.vic.gov.au)