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What is the average length of the menstrual cycle?
What is the average length of the menstrual cycle?
Which hormone is responsible for stimulating the pituitary gland to release gonadotropins?
Which hormone is responsible for stimulating the pituitary gland to release gonadotropins?
At what average age does menopause typically occur?
At what average age does menopause typically occur?
What triggers the first menstrual period, known as menarche, in females?
What triggers the first menstrual period, known as menarche, in females?
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Which hormone is released from the pituitary gland and is essential for the ovarian cycle?
Which hormone is released from the pituitary gland and is essential for the ovarian cycle?
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What is the term for menstruation that occurs before the age of 45?
What is the term for menstruation that occurs before the age of 45?
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What factors can influence the timing of menarche?
What factors can influence the timing of menarche?
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What are the primary hormones secreted by the ovaries during the menstrual cycle?
What are the primary hormones secreted by the ovaries during the menstrual cycle?
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What hormone surge triggers ovulation during the ovarian cycle?
What hormone surge triggers ovulation during the ovarian cycle?
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What happens to the corpus luteum if the released ovum is not fertilized?
What happens to the corpus luteum if the released ovum is not fertilized?
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During which phase of the cycle is the mature ovum released?
During which phase of the cycle is the mature ovum released?
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What role does human chorionic gonadotropins (HCG) play after fertilization?
What role does human chorionic gonadotropins (HCG) play after fertilization?
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What hormone is primarily responsible for stimulating the secretion of estrogen during the follicular phase?
What hormone is primarily responsible for stimulating the secretion of estrogen during the follicular phase?
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What is the primary function of the corpus luteum?
What is the primary function of the corpus luteum?
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What initiates the secretion of FSH during the feedback mechanism?
What initiates the secretion of FSH during the feedback mechanism?
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What occurs at mid-cycle around day 12 or 13 in relation to luteinizing hormone (LH)?
What occurs at mid-cycle around day 12 or 13 in relation to luteinizing hormone (LH)?
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During which phase of the ovarian cycle does a primordial follicle develop into a mature Graafian follicle?
During which phase of the ovarian cycle does a primordial follicle develop into a mature Graafian follicle?
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What occurs to an unfertilized ovum after being released?
What occurs to an unfertilized ovum after being released?
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What is the first phase of the uterine cycle called?
What is the first phase of the uterine cycle called?
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What role does prolactin possibly play in the menstrual cycle?
What role does prolactin possibly play in the menstrual cycle?
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What happens to the empty follicle after ovulation?
What happens to the empty follicle after ovulation?
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How long does the luteal phase last in the ovarian cycle?
How long does the luteal phase last in the ovarian cycle?
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Which hormone combination is crucial for the event of ovulation?
Which hormone combination is crucial for the event of ovulation?
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During which phase of the uterine cycle does the endometrium thicken in preparation for a possible pregnancy?
During which phase of the uterine cycle does the endometrium thicken in preparation for a possible pregnancy?
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What is the average duration of normal menstruation?
What is the average duration of normal menstruation?
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What hormone is primarily responsible for the proliferation of the endometrium during the proliferative phase?
What hormone is primarily responsible for the proliferation of the endometrium during the proliferative phase?
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During the secretory phase, which hormone does the corpus luteum produce?
During the secretory phase, which hormone does the corpus luteum produce?
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What does the presence of dark red color in menstrual flow indicate?
What does the presence of dark red color in menstrual flow indicate?
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What is the typical composition of menstrual flow?
What is the typical composition of menstrual flow?
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What happens to the endometrium shortly after menstruation ends?
What happens to the endometrium shortly after menstruation ends?
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What occurs in the endometrium just before ovulation?
What occurs in the endometrium just before ovulation?
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How does progesterone affect the uterus during the secretory phase?
How does progesterone affect the uterus during the secretory phase?
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Study Notes
Introduction
- The menstrual cycle is a monthly process involving the ripening and release of a mature egg and the preparation of the uterus for pregnancy.
- It occurs repeatedly between menarche (first menstrual period) and menopause (cessation of cycles).
- The average age of menarche is 12-13 years, with a normal range of 8-16 years.
- Factors like heredity, diet, and overall health can influence the age of menarche.
- The length of the menstrual cycle varies greatly, ranging from 21 to 35 days, with an average of 28 days.
- Menopause typically occurs around 52 years old, with a common range of 45-55 years. Menopause before 45 is considered premature.
Endocrine Control
- The hypothalamus releases gonadotropin-releasing hormone (GnRH) or luteinizing releasing hormone (LHRH).
- The pituitary gland produces follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
- The ovaries produce estrogen and progesterone.
Hypothalamic-Pituitary-Ovarian Axis
- The hypothalamus controls the secretion of pituitary hormones and is influenced by the central nervous system.
- GnRH from the hypothalamus stimulates the anterior pituitary to release gonadotropins (FSH and LH).
- The anterior pituitary controls ovarian function through cyclic secretion of gonadotropins.
Follicle-Stimulating Hormone (FSH)
- FSH levels rise in the late previous cycle and peak around day 5 of the new cycle, before rising again around day 12.
- FSH is responsible for:
- Ripening and maturation of ovarian Graafian follicles.
- Stimulating estrogen secretion by growing follicles.
- Contributing to ovulation alongside LH.
Luteinizing Hormone (LH)
- LH levels remain relatively constant except for a sudden peak around day 12 or 13 of the cycle.
- LH is responsible for:
- Promoting follicular ripening alongside FSH.
- Triggering ovulation (rupture of the mature Graafian follicle).
- Transformation of the ruptured follicle into the corpus luteum.
- Stimulating the corpus luteum to produce estrogen and progesterone.
Prolactin
- Prolactin release is inhibited by FSH and LH.
- Its role in ovulation control is not fully understood, but it may prevent further ovulation after fertilization.
Physiology of the Menstrual Cycle
- The cycle is divided into the ovarian cycle and the uterine cycle.
The Ovarian Cycle
- Consists of three phases:
- Follicular phase (day 1-13)
- Ovulatory phase (day 14)
- Luteal phase (day 15-28)
Follicular Phase (Day 1-13)
- FSH stimulates the development of a primordial follicle into a mature Graafian follicle.
- Multiple follicles may start maturing, but usually only one reaches full maturity and ovulates.
- The empty follicle (corpus luteum) eventually atrophies, becoming the corpus albicans.
- As the Graafian follicle matures, it increasingly produces estrogen, which inhibits FSH secretion (negative feedback).
Ovulatory Phase (Day 14)
- Ovulation is the release of a mature ovum from the Graafian follicle into the fallopian tube.
- The LH surge, starting around day 12 and lasting 48 hours, triggers ovulation.
- The mature ovum is about 20 mm in diameter.
- Once released, the ovum is swept into the fallopian tube by the fimbria.
- An unfertilized ovum disintegrates in the fallopian tube after about a day.
- Fertilization usually occurs in the ampulla of the fallopian tube.
- A fertilized ovum undergoes embryogenesis.
Luteal Phase (Day 15-28)
- The empty follicle (corpus luteum) produces estrogen and progesterone.
- If the ovum is not fertilized, the corpus luteum degenerates, estrogen and progesterone levels fall, and menstruation begins.
- If the ovum is fertilized, the developing embryo secretes human chorionic gonadotropin (HCG), which prevents the degeneration of the corpus luteum.
- The corpus luteum continues to produce estrogen and progesterone, preventing menstruation and indicating pregnancy.
Menstrual Cycle Feedback Mechanisms
- Decreased estrogen levels stimulate the hypothalamus to release GnRH at a higher rate (positive feedback).
- Increased GnRH stimulates the anterior pituitary to produce FSH (positive feedback).
- Increased estrogen levels inhibit GnRH release (negative feedback).
The Uterine Cycle
- Consists of three phases:
- Menstruation
- Proliferative phase
- Secretory phase
Menstruation
- The first phase of the uterine cycle, marking non-pregnancy.
- Involves periodic shedding of the endometrium with blood loss.
- Occurs due to the degeneration of the corpus luteum.
- Normal menstruation lasts 3-5 days, but 2-7 days is considered normal.
- Average blood loss is 50-80 ml.
- Menstrual flow is typically dark red and consists of red blood cells, cervical mucus, epithelial cells, and bacteria.
Proliferative Phase
- The second phase, where estrogen stimulates endometrial growth (proliferation).
- Maturing ovarian follicles secrete increasing amounts of estradiol.
- Estrogen initiates the formation of a new endometrial layer.
- It also stimulates cervical crypts to produce fertile cervical mucus.
Secretory Phase
- The final phase of the uterine cycle, where progesterone, produced by the corpus luteum, prepares the endometrium for implantation.
- Progesterone increases blood flow and uterine secretions, while reducing uterine muscle contractility.
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Description
Explore the phases of the menstrual cycle, from menarche to menopause, and understand the endocrine control involved. This quiz covers key hormonal interactions and factors affecting menstrual health, providing essential insights into a vital physiological process.
