Introduction
Complex interactions among hormones control the start of menstruation during puberty, the rhythms and duration of menstrual cycles during the reproductive years, and the end of menstruation at menopause. Hormonal control of menstruation begins in the hypothalamus (the part of the brain that coordinates and controls hormonal activity). The hypothalamus releases gonadotropin-releasing hormone in pulses. This hormone stimulates the pituitary gland to produce two hormones called gonadotropins: luteinizing hormone and follicle-stimulating hormone. These hormones stimulate the ovaries. The ovaries produce the female hormones estrogen and progesterone (see Section 22, Chapter 241), which ultimately control menstruation. Hormones produced by other glands, such as the adrenal glands and the thyroid gland, can also affect the functioning of the ovaries and menstruation.
Menstrual disorders include premenstrual syndrome, dysmenorrhea, and amenorrhea. Vaginal bleeding may be abnormal during the reproductive years when menstrual periods are too heavy or too light, last too long, occur too often, or are irregular. Any vaginal bleeding that occurs before puberty or after menopause is abnormal until proven otherwise.
 See the table Deciphering Medical Terms for Menstrual Disorders.
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