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 (at menarche) and stops permanently at menopause. (Menopause is defined as 1 year after the last menstrual cycle.)
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 produce estrogen and progesterone. Estrogen and progesterone stimulate the uterus and breasts to prepare for possible fertilization.
Hormones play a crucial role in regulating the menstrual cycle, which is a complex series of events that occur in the female reproductive system, typically lasting about 28 days. The key hormones involved in the menstrual cycle are:
1. **Follicle-Stimulating Hormone (FSH):** Secreted by the pituitary gland, FSH stimulates the growth and development of follicles (small sacs containing immature eggs) in the ovaries.
2. **Luteinizing Hormone (LH):** Also produced by the pituitary gland, LH triggers the release of a mature egg from a follicle in a process known as ovulation.
3. **Estrogen:** Produced mainly by the ovaries, estrogen levels rise during the follicular phase of the menstrual cycle. Estrogen stimulates the thickening of the uterine lining (endometrium) in preparation for a potential pregnancy.
4. **Progesterone:** After ovulation, the ruptured follicle transforms into a structure called the corpus luteum, which produces progesterone. Progesterone helps maintain the thickened endometrium, making it more receptive to a fertilized egg. If fertilization occurs, progesterone continues to support early pregnancy.
The menstrual cycle can be divided into several phases:
- **Menstruation:** The cycle begins with the shedding of the uterine lining if no pregnancy occurred during the previous cycle.
- **Follicular Phase:** FSH stimulates the development of follicles, and rising estrogen levels prepare the uterus for a potential pregnancy.
- **Ovulation:** LH surge triggers the release of an egg from a mature follicle.
- **Luteal Phase:** The corpus luteum forms after ovulation, producing progesterone. If fertilization doesn't occur, the corpus luteum degenerates, leading to a decline in progesterone and triggering the start of menstruation.
Hormones coordinate these events, ensuring the proper development and release of eggs, preparation of the uterine lining, and support for a potential pregnancy. If fertilization doesn't occur, hormonal changes initiate the shedding of the uterine lining, starting a new menstrual cycle.
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Answer:
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 (at menarche) and stops permanently at menopause. (Menopause is defined as 1 year after the last menstrual cycle.)
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 produce estrogen and progesterone. Estrogen and progesterone stimulate the uterus and breasts to prepare for possible fertilization.
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Answer:
Hormones play a crucial role in regulating the menstrual cycle, which is a complex series of events that occur in the female reproductive system, typically lasting about 28 days. The key hormones involved in the menstrual cycle are:
1. **Follicle-Stimulating Hormone (FSH):** Secreted by the pituitary gland, FSH stimulates the growth and development of follicles (small sacs containing immature eggs) in the ovaries.
2. **Luteinizing Hormone (LH):** Also produced by the pituitary gland, LH triggers the release of a mature egg from a follicle in a process known as ovulation.
3. **Estrogen:** Produced mainly by the ovaries, estrogen levels rise during the follicular phase of the menstrual cycle. Estrogen stimulates the thickening of the uterine lining (endometrium) in preparation for a potential pregnancy.
4. **Progesterone:** After ovulation, the ruptured follicle transforms into a structure called the corpus luteum, which produces progesterone. Progesterone helps maintain the thickened endometrium, making it more receptive to a fertilized egg. If fertilization occurs, progesterone continues to support early pregnancy.
The menstrual cycle can be divided into several phases:
- **Menstruation:** The cycle begins with the shedding of the uterine lining if no pregnancy occurred during the previous cycle.
- **Follicular Phase:** FSH stimulates the development of follicles, and rising estrogen levels prepare the uterus for a potential pregnancy.
- **Ovulation:** LH surge triggers the release of an egg from a mature follicle.
- **Luteal Phase:** The corpus luteum forms after ovulation, producing progesterone. If fertilization doesn't occur, the corpus luteum degenerates, leading to a decline in progesterone and triggering the start of menstruation.
Hormones coordinate these events, ensuring the proper development and release of eggs, preparation of the uterine lining, and support for a potential pregnancy. If fertilization doesn't occur, hormonal changes initiate the shedding of the uterine lining, starting a new menstrual cycle.