Questions and Answers
What is the duration of the luteal phase in the menstrual cycle?
What hormone triggers ovulation during the menstrual cycle?
Which phase of the menstrual cycle occurs between days 1 to 14?
What role do granulosa cells play in the follicular phase?
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What happens to the follicle after ovulation?
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What does the hypothalamus release to initiate the menstrual cycle?
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What is the main role of progesterone during the luteal phase?
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Which structure is primarily responsible for hormone production in the menstrual cycle?
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What occurs around day 14 of the menstrual cycle?
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What is the purpose of the cervix in the menstrual cycle?
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What hormone is produced by the embryo to preserve the corpus luteum if fertilization occurs?
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What causes the onset of menstruation if fertilization does not occur?
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During menstruation, which layers of the endometrium are shed?
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At what points does Follicle Stimulating Hormone (FSH) peak during the menstrual cycle?
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What happens to progesterone levels during the luteal phase?
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What occurs when estrogen and progesterone levels drop after the corpus luteum degenerates?
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What is the main physiological change in the body during the menstruation phase of the cycle?
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How do estrogen levels behave during the follicular phase?
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What is the role of Luteinizing Hormone (LH) before ovulation?
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Study Notes
Menstrual Cycle Overview
- Typical menstrual cycle lasts about 28 days, divided into two phases: follicular and luteal.
- Follicular phase occurs from day 1 to 14; luteal phase spans from day 15 to 28.
- Cycle lengths may vary between 21 to 35 days while luteal phase consistently lasts 14 days.
Key Hormones
- Follicle Stimulating Hormone (FSH): Stimulates follicle development in ovaries.
- Luteinizing Hormone (LH): Triggers ovulation.
- Estrogen: Secretes from developing follicles; responsible for female secondary sexual characteristics and endometrial growth.
- Progesterone: Produced by corpus luteum post-ovulation; maintains endometrial lining.
Key Structures
- Hypothalamus: Initiates hormonal regulation by releasing gonadotropin-releasing hormone (GnRH).
- Pituitary Gland: Divided into anterior (produces FSH and LH) and posterior sections.
- Ovaries: Site of egg maturation and hormone production.
- Uterus: Houses the endometrium, where a fertilized egg implants and grows.
- Cervix: Regulates passage of sperm and menstrual fluid.
Cycle Initiation
- Day 1 marks the start of menstruation; hypothalamus releases GnRH.
- GnRH stimulates anterior pituitary to secrete FSH and LH, commencing follicle growth.
Follicular Phase
- FSH promotes development of 15-20 primordial follicles, each containing an immature egg.
- Granulosa cells in developing follicles secrete estrogen; rising levels lead to breast tissue development and endometrium thickening.
- Estrogen has a negative feedback effect on FSH and LH until the lead follicle prepares for ovulation.
Ovulation
- Occurs around day 14; marked by a spike in LH, causing the release of the ovum from the dominant follicle.
- Follicle collapses, forming the corpus luteum.
Luteal Phase
- Corpus luteum secretes high levels of progesterone and some estrogen to support endometrial maintenance.
- If fertilization occurs, the embryo produces human chorionic gonadotropin (HCG) to preserve the corpus luteum.
- If no fertilization, corpus luteum degenerates, causing drops in estrogen and progesterone, which leads to the breakdown of endometrial lining and onset of menstruation.
Menstruation
- Menstruation involves the shedding of the endometrium's superficial and middle layers, lasting between 1 to 8 days.
- Blood and fluid are expelled through the cervix and vagina, marking the cycle's restart.
Hormonal Levels Throughout the Cycle
- FSH: Peaks at the start and just before ovulation.
- Estrogen: Rises during follicular phase, dips slightly before ovulation, then spikes then falls.
- LH: Remains low until a spike right before ovulation.
- Progesterone: Low in the follicular phase, increases during the luteal phase.
- Following degeneration of the corpus luteum, estrogen and progesterone levels drop, leading to menstruation.
Conclusion
- Understanding the menstrual cycle involves knowing hormone interactions, phases, and physiological changes in the body that prepare for potential pregnancy.
Menstrual Cycle Overview
- Typical menstrual cycle lasts approximately 28 days, divided into two main phases: follicular and luteal.
- Follicular phase spans from day 1 to 14, while the luteal phase runs from day 15 to 28.
- Cycle lengths can vary from 21 to 35 days, but the luteal phase consistently lasts around 14 days.
Key Hormones
- Follicle Stimulating Hormone (FSH): Vital for stimulating the development of ovarian follicles.
- Luteinizing Hormone (LH): Key player in triggering ovulation.
- Estrogen: Secreted from developing follicles; crucial for the development of female secondary sexual characteristics and stimulating endometrial growth.
- Progesterone: Produced by the corpus luteum after ovulation; essential for maintaining the endometrial lining.
Key Structures
- Hypothalamus: Initiates hormonal regulation by releasing gonadotropin-releasing hormone (GnRH).
- Pituitary Gland: Composed of anterior (produces FSH and LH) and posterior sections.
- Ovaries: Responsible for egg maturation and hormone production.
- Uterus: Contains the endometrium; the site for fertilized egg implantation and growth.
- Cervix: Regulates the passage of sperm and menstrual fluid.
Cycle Initiation
- Day 1 of the cycle marks the onset of menstruation; hypothalamus releases GnRH.
- GnRH stimulates the anterior pituitary to secrete FSH and LH, initiating follicle growth.
Follicular Phase
- FSH encourages the development of 15-20 primordial follicles, each containing an immature egg.
- Granulosa cells in the developing follicles produce estrogen, which promotes breast tissue growth and thickening of the endometrium.
- Rising estrogen levels exert negative feedback on FSH and LH, modulating their release until the lead follicle is ready for ovulation.
Ovulation
- Occurs around day 14, highlighted by an LH spike that triggers the release of the ovum from the dominant follicle.
- Following ovulation, the follicle collapses and transforms into the corpus luteum.
Luteal Phase
- The corpus luteum secretes high levels of progesterone and some estrogen, crucial for endometrial maintenance.
- If fertilization occurs, the embryo produces human chorionic gonadotropin (HCG) to sustain the corpus luteum.
- In absence of fertilization, the corpus luteum degenerates, leading to decreased estrogen and progesterone levels, which triggers the breakdown of the endometrial lining and the onset of menstruation.
Menstruation
- Menstruation involves the shedding of the endometrium's superficial and middle layers, lasting between 1 to 8 days.
- Blood and fluid are expelled through the cervix and vagina, signaling the reboot of the menstrual cycle.
Hormonal Levels Throughout the Cycle
- FSH: Peaks at the onset of menstruation and just before ovulation.
- Estrogen: Increases during the follicular phase, dips slightly before ovulation, then spikes and subsequently falls.
- LH: Generally remains low until a significant spike occurs just prior to ovulation.
- Progesterone: Levels are low during the follicular phase, rise during the luteal phase, and fall following the degeneration of the corpus luteum, resulting in menstruation.
Conclusion
- Understanding the menstrual cycle is essential for recognizing the interactions between hormones, the phases involved, and the physiological changes that prepare the body for potential pregnancy.
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Description
Explore the intricacies of the menstrual cycle, which typically lasts about 28 days and consists of the follicular and luteal phases. Discover key hormones involved, such as FSH, LH, estrogen, and progesterone, as well as the important structures like the ovaries and uterus that play crucial roles in this process.
