The menstrual cycle is typically counted from which day?
The day of ovulation
The first day of menstrual bleeding
The last day of menstruation
The day the LH surge begins
The Correct Answer is B
The menstrual cycle is a recurring sequence of hormonal and physiological events typically lasting 21–35 days, with an average of 28 days. It is counted from day 1, which is defined as the first day of menstrual bleeding—the visible onset of endometrial shedding. This marks the start of the follicular phase, during which FSH (normal range: 3–20 IU/L) rises to stimulate follicular development. Bleeding lasts about 3–7 days, and estrogen levels gradually increase to rebuild the endometrium. Ovulation generally occurs around day 14, followed by the luteal phase.
Rationale for correct answer
B. The first day of menstrual bleeding is considered day 1 of the cycle. It marks the beginning of the follicular phase and is used clinically to track ovulation, fertility windows, and menstrual regularity.
Rationale for incorrect answers
A. Ovulation typically occurs around day 14 of a 28-day cycle, not at the beginning. It is a mid-cycle event and not used as the starting point for cycle calculation.
C. The last day of menstruation varies among individuals and does not consistently mark the start of a new hormonal cycle, making it an unreliable reference point.
D. The LH surge precedes ovulation by 24–36 hours and occurs around day 13–14, mid-cycle. It is not the beginning of the menstrual cycle and occurs much later than day 1.
Take home points
- Day 1 of the menstrual cycle is the first day of menstrual bleeding.
- This marks the start of the follicular phase and FSH rise.
- Ovulation and the LH surge occur mid-cycle, not at the beginning.
- Accurate cycle tracking begins with the first day of menstruation.
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Correct Answer is D
Explanation
The menstrual cycle is divided into the menstrual, follicular, ovulatory, and luteal phases, regulated by hormonal fluctuations of estrogen, progesterone, FSH, and LH. The menstrual phase begins on day 1 of the cycle and lasts about 3–7 days, during which the functional layer of the endometrium is shed due to a sudden drop in progesterone (from normal mid-luteal values of 5–20 ng/mL to <1 ng/mL) after corpus luteum regression. FSH (normal: 3–20 IU/L) begins to rise to recruit new follicles. Blood loss ranges from 30–80 mL, and prostaglandins contribute to uterine contractions and cramping.
Rationale for correct answer
D. The menstrual phase involves the shedding of the functional layer of the endometrium due to the withdrawal of progesterone and estrogen. It marks the beginning of a new cycle.
Rationale for incorrect answers
A. The follicular phase follows menstruation and involves regeneration of the endometrium under the influence of rising estrogen levels from developing follicles.
B. Ovulation is the release of an ovum due to the LH surge, around day 14. The endometrium is not shed during this phase; it continues to thicken in preparation for implantation.
C. The luteal phase occurs after ovulation and is marked by progesterone secretion from the corpus luteum to maintain the endometrium. Shedding occurs only if implantation does not happen.
Take home points
- The menstrual phase is when endometrial shedding occurs due to hormonal withdrawal.
- Estrogen and progesterone drop sharply, triggering menstruation.
- The follicular phase is for endometrial regeneration, not shedding.
- Luteal phase maintains the endometrium; shedding starts only if it ends.
Correct Answer is C
Explanation
Estrogen function in the menstrual cycle
Estrogen is a key steroid hormone secreted primarily by the granulosa cells of the developing follicle. It plays a central role in the follicular phase of the menstrual cycle by stimulating endometrial proliferation, enhancing FSH receptor expression in follicles, and exerting negative feedback on FSH and positive feedback on LH as ovulation approaches. Normal estradiol (E2) levels range from 30–400 pg/mL, peaking around 200–300 pg/mL just before ovulation. Estrogen also supports cervical mucus thinning to facilitate sperm transport and primes the endometrium for possible implantation.
Rationale for correct answer
C. Estrogen stimulates mitotic activity and proliferation of the endometrial functional layer during the follicular phase. This prepares the uterine lining for potential implantation post-ovulation.
Rationale for incorrect answers
A. Ovulation is triggered by a surge in LH, not directly by estrogen. Estrogen contributes indirectly by reaching a threshold that induces the LH surge, but it does not trigger ovulation by itself.
B. Maintenance of the corpus luteum is supported by LH and, if pregnancy occurs, human chorionic gonadotropin (hCG). Estrogen does not sustain corpus luteum function.
D. Estrogen initially inhibits FSH secretion via negative feedback, but this is not its primary role. Its main function is endometrial proliferation and preparing the body for ovulation.
Take home points
- Estrogen stimulates the endometrial lining to proliferate during the follicular phase.
- LH, not estrogen, is the primary trigger for ovulation.
- Corpus luteum maintenance depends on LH or hCG, not estrogen.
- Estrogen has a dual feedback effect on FSH depending on its concentration and timing.
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