Menstrual cycle hormones: identifying the missing one from graph patterns

Steps:

• Recall standard menstrual cycle: FSH rises early, LH surges mid-cycle for ovulation, oestrogen peaks just before LH surge, progesterone rises post-ovulation.
• Examine graph labels and peaks: two gonadotropins (FSH, LH) show early and mid-cycle surges.
• Identify post-ovulation plateau as progesterone.
• Note absence of pre-ovulation rising curve, which defines oestrogen.

Why C is correct:

• Oestrogen drives follicular development with a characteristic pre-ovulatory peak triggering LH surge, absent in the graph per standard endocrine physiology.

Why the others are wrong:

• A: FSH is shown with its follicular phase rise and minor mid-cycle peak.
• B: LH is shown with its prominent ovulatory surge.
• D: Progesterone is shown with its luteal phase elevation after ovulation.

Final answer: C