Key Points Summary — Menstrual Cycle Phases and Hormones — Summary

The menstrual cycle averages 28 days; regulated by the hypothalamus-pituitary-ovarian axis.
Menstrual phase (days 1–5): Progesterone and estrogen fall (corpus luteum degenerates) → endometrial shedding.
Follicular/Proliferative phase (days 6–13): FSH rises → follicle grows → estrogen secreted → endometrium rebuilds/proliferates.
Ovulation (~day 14): LH surge (triggered by rising estrogen's positive feedback) → Graafian follicle ruptures → secondary oocyte released.
Luteal/Secretory phase (days 15–28): Ruptured follicle → corpus luteum → secretes progesterone (and estrogen) → endometrium becomes thick and glandular.
No fertilization: Corpus luteum degenerates at ~day 28 → progesterone falls → menstruation begins → new cycle.
Critical NEET points:
- LH surge (not FSH) = ovulation trigger
- Progesterone (from corpus luteum, not estrogen) = secretory endometrium
- Falling progesterone = menstruation trigger
- hCG (from trophoblast) = corpus luteum maintainer in pregnancy