women s health issues
Menstrual Cycle
Introduction
Menstruation is the shedding of the lining of the uterus (endometrium) accompanied by bleeding. It occurs in approximately monthly cycles throughout a woman's reproductive life, except during pregnancy. Menstruation starts during Puberty in Girls (at menarche) and stops permanently at By definition, the menstrual cycle begins with the first day of bleeding, which is counted as day 1. The cycle ends just before the next menstrual period. Menstrual cycles normally range from about 24 to 38 days. Only 10 to 15% of women have cycles that are exactly 28 days. Also, in at least 20% of women, cycles are irregular. That is, they are longer or shorter than the normal range. Usually, the cycles vary the most and the intervals between periods are longest in the years immediately after menstruation starts (menarche) and before menopause. Normally, menstrual bleeding lasts 4 to 8 days. Blood loss during a cycle usually ranges from 1/5 to 2 1/2 ounces. A sanitary pad or tampon, depending on the type, can hold up to an ounce of blood. Menstrual blood, unlike blood resulting from an injury, usually does not clot unless the bleeding is very heavy. The menstrual cycle is regulated by hormones. Luteinizing hormone and follicle-stimulating hormone, which are produced by the pituitary gland, promote ovulation and stimulate the ovaries to produceestrogenandprogesterone.Estrogenandprogesteronestimulate the uterus and breasts to prepare for possible fertilization. The menstrual cycle has three phases: Follicular (before release of the egg) Ovulatory (egg release) Luteal (after egg release) The menstrual cycle is regulated by the complex interaction of hormones: luteinizing hormone, follicle-stimulating hormone, and the female sex hormonesestrogenandprogesterone. The menstrual cycle has three phases: Follicular (before release of the egg) Ovulatory (egg release) Luteal (after egg release) The menstrual cycle begins with menstrual bleeding (menstruation), which marks the first day of the follicular phase. When thefollicular phasebegins, levels ofestrogenandprogesteroneare low. As a result, the top layers of the thickened lining of the uterus (endometrium) break down and are shed, and menstrual bleeding occurs. About this time, the follicle-stimulating hormone level increases slightly, stimulating the development of several follicles in the ovaries. (Follicles are sacs filled with fluid.) Each follicle contains an egg. Later in this phase, as the follicle-stimulating hormone level decreases, usually only one follicle continues to develop. This follicle producesestrogen.Estrogenlevels increase steadily. Theovulatory phasebegins with a surge in luteinizing hormone and follicle-stimulating hormone levels. Luteinizing hormone stimulates egg release (ovulation), which usually occurs 16 to 32 hours after the surge begins. Theestrogenlevel decreases during the surge, and theprogesteronelevel starts to increase. During theluteal phase,luteinizing hormone and follicle-stimulating hormone levels decrease. The ruptured follicle closes after releasing the egg and forms a corpus luteum, which producesprogesterone. During most of this phase, theestrogenlevel is high.Progesteroneandestrogencause the lining of the uterus to thicken more, to prepare for possible fertilization. If the egg is not fertilized, the corpus luteum degenerates and no longer producesprogesterone, theestrogenlevel decreases, the top layers of the lining break down and are shed, and menstrual bleeding occurs (the start of a new menstrual cycle). If the egg is fertilized, the corpus luteum continues to function during early pregnancy. It helps maintain the pregnancy. 