The menstrual cycle begins on the first day of menstruation (a periodic discharge of bloody fluid from the uterus) and ends the day before the following menstruation, which is roughly 28 days, although this may vary from woman to woman. The period between the first menstruation or menarche and menopause is a woman’s fertile period. This goes from puberty (around age 12) to about age 55, give or take.
The ovarian menstrual cycle is ruled by the action of hormones, which prepare a few structures for the possible arrival of a fertilized embryo. Follicle stimulating hormone (FSH) and luteinizing hormone (LH) play an important role in the development of the ovum within the ovary and in preparing the walls of the uterus to receive the embryo. The first days of the cycle, around 20 or so follicles start to mature and progressively secrete estrogens, causing the blood vessels of the endometrium to elongate.
Over the next 10 to 14 days, the follicles will contain a mature ovum, and estrogen levels start to decline. The pituitary gland starts secreting LH, which acts on follicles, until one of them releases the ovum towards the fallopian tube, thus producing ovulation.
