For most women, the menstrual period occurs once a month and lasts from three to five days. The menstrual cycle provides the hormones estrogen and progesterone, which rise and fall during the month to control the cycle. The average menstrual cycle lasts 28 days. But in adults it can range anywhere from 21 to 35 days, and in teens can range from 21 to 45 days. Estrogen levels begin to rise in the first half of the cycle, which prompts the lining of the uterus to grow and thicken.
This lining nourishes the embryo if a pregnancy occurs. During this same time frame, an egg in one of the ovaries begins to mature. About half way through the menstrual cycle ovulation takes place. Ovulation is when the egg leaves the ovary. The egg will then begin traveling through the fallopian tube toward the uterus. During this time, hormone levels continue to rise and help prepare the wall of the uterus for pregnancy. Women are most likely to get pregnant during the three days prior to, or on the day of ovulation.
If the egg is not fertilized, hormone levels drop, which signals for the next menstrual cycle to begin and the egg will be shed with the uterine lining in the next period. The amount of blood, called the menstrual flow, could be light, moderate or heavy. The length of the period also varies in women, with most periods lasting between three and five days.
As a woman matures, her cycle tends to shorten and become more regular. In the United States, the average age a girl starts her period is 12, but it can start as early as 8 or as late as If a girl has not started her period by age 15 or two to three years since breast growth started, she should make an appointment with her healthcare provider. A woman usually has her periods until menopause, which occurs between the ages of 45 and During menopause a woman stops ovulating releasing eggs and can no longer get pregnant.
A woman is generally most likely to get pregnant fertile if she has sex a few days before, and during ovulation. Menstruation is one part of a woman's cycle when the lining of the uterus endometrium is shed. This occurs throughout a woman's reproductive life.
With each monthly cycle, the endometrium prepares itself to nourish a fetus. Increased levels of estrogen and progesterone help thicken its walls. If fertilization does not occur, the endometrium, along with blood and mucus from the vagina and cervix make up the menstrual flow that leaves the body through the vagina during the period.
On average, a young woman in the U. This is generally 2 to 3 years after her breasts start to grow. This is also soon after she notices pubic and underarm hair. Menstrual cycles normally range from about 25 to 36 days.
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. Menstrual bleeding lasts 3 to 7 days, averaging 5 days. 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 produce estrogen and progesterone.
Estrogen and progesterone stimulate the uterus and breasts to prepare for possible fertilization. The menstrual cycle is regulated by the complex interaction of hormones: luteinizing hormone, follicle-stimulating hormone, and the female sex hormones estrogen and progesterone. The menstrual cycle begins with menstrual bleeding menstruation , which marks the first day of the follicular phase.
When the follicular phase begins, levels of estrogen and progesterone are 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.
Each follicle contains an egg. Later in this phase, as the follicle-stimulating hormone level decreases, only one follicle continues to develop. This follicle produces estrogen. The ovulatory phase begins 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. The estrogen level decreases during the surge, and the progesterone level starts to increase. During the luteal phase, luteinizing hormone and follicle-stimulating hormone levels decrease. The ruptured follicle closes after releasing the egg and forms a corpus luteum, which produces progesterone.
During most of this phase, the estrogen level is high. Progesterone and estrogen cause 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 produces progesterone , the estrogen level 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. The follicular phase begins on the first day of menstrual bleeding day 1. But the main event in this phase is the development of follicles in the ovaries. At the beginning of the follicular phase, the lining of the uterus endometrium is thick with fluids and nutrients designed to nourish an embryo.
If no egg has been fertilized, estrogen and progesterone levels are low. As a result, the top layers of the endometrium are shed, and menstrual bleeding occurs. About this time, the pituitary gland slightly increases its production of follicle-stimulating hormone. This hormone then stimulates the growth of 3 to 30 follicles. Later in the phase, as the level of this hormone decreases, only one of these follicles called the dominant follicle continues to grow.
It soon begins to produce estrogen , and the other stimulated follicles begin to break down.
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