The menstrual cycle is a monthly loop between the brain, the ovaries and the uterus that prepares the body for pregnancy. A typical cycle lasts about 28 days, with a normal range of about 21 to 35 days.
Follicular phase
From day 1 of bleeding, FSH from the pituitary makes ovarian follicles grow. The leading follicle releases rising estrogen, which rebuilds the endometrium.
Ovulation
High estrogen triggers a surge of LH, and the egg is released about a day later, around day 14 of a 28-day cycle. Some people feel brief one-sided pelvic pain at this time.
Luteal phase
The empty follicle becomes the corpus luteum, which makes progesterone to keep the lining ready. This phase is fairly fixed at about 14 days.
Menstruation
If no pregnancy occurs, the corpus luteum fades, progesterone falls and the lining sheds. Bleeding usually lasts 2 to 7 days.
| Phase | Main hormones | Uterine lining |
|---|---|---|
| Follicular (days 1 to 13) | FSH, rising estrogen | Sheds, then rebuilds |
| Ovulation (about day 14) | LH surge | Thick |
| Luteal (days 15 to 28) | Progesterone | Secretory, ready for implantation |
At the bedside
Always ask the first day of the last menstrual period; it dates a pregnancy and flags a late period. Any missed period in someone who could be pregnant needs a pregnancy test.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).