Menstrual Cycle PhasesPhase 1: Menstruation
Days 1-7: The surface of the endometrium breaks down into a bloody fluid. It flows from the uterus through the cervix and leaves the body through the vagina. A normal period lasts three to seven days. Phase 2: Egg prepares to leave the ovary
Days 6-12 (or more): The pituitary gland signals the ovaries to release estrogen and progesterone, the hormones responsible for the menstrual cycle. The hormone estrogen causes the endometrium to thicken and get ready for feeding and protecting the embryo. The hormone progesterone maintains this lining until the female is pregnant and throughout pregnancy, or until menstruation begins. Phase 3: Ovulation
Days 13-15 (before next period): The pituitary gland signals the release of follicle stimulating hormone (FSH) and luteinizing hormone (LH). FSH causes eggs to develop in the ovary. LH causes the release of one (or more) mature egg(s), which then enters the fallopian tube. Phase 4: Lining continues to thicken
After ovulation: The egg travels down the fallopian tube toward the uterus. If the egg is not fertilized by a sperm cell or does not implant, the surface of the endometrium is no longer needed and is then ready to be shed. The cycle is complete and menstruation will begin again. For more info on menstruation, check out Menstrual Cycle Facts. Last revised: April 21, 2008 | 
