Hormones in the Menstrual Cycle and Fertility
Four hormones run the monthly cycle: FSH and LH from the pituitary, oestrogen and progesterone from the ovaries. The same loop explains how hormonal contraception and fertility treatment work.
What a learner can do afterwards
- Places each of the four hormones on a cycle diagram and states what it triggers.
- Explains how keeping oestrogen high stops an egg being released.
- Explains what fertility treatment adds and why it can lead to more than one embryo.
1 · Read
Just as insulin and glucagon answered drifts in blood glucose, four hormones run the monthly cycle from two control rooms. The pituitary in the brain releases FSH and LH. The ovaries release oestrogen and progesterone. FSH grows the follicle. Oestrogen builds the lining. LH releases the egg. Progesterone keeps the lining ready. Cycle diagrams show one common pattern. Real cycle lengths vary, so treat days on a diagram as an example, not a rule.
Follow one common 28-day example in order. FSH grows the follicle holding the egg, and the growing follicle makes oestrogen. Rising oestrogen builds the uterus lining. Near the middle a high preovulatory rise can flip the loop and trigger a surge of LH, and that surge releases the egg. The leftover follicle then makes progesterone.
Combined hormonal contraception uses oestrogen plus progestin to steady the loop. Steady levels stop an LH surge from building, so no egg is released. This differs from the natural mid-cycle rise, which can trigger the surge. No doses or schedules here. Method choice stays between a person and their clinician.
Fertility stimulation can push the ovaries to mature more than one follicle at once. More follicles can release more eggs. Each embryo still needs fertilisation, and treatments vary from person to person. That is why twins are more likely, never automatic. Steady levels of oestrogen plus progestin do the opposite at the other end of the same loop, blocking release instead of growing follicles.
After ovulation progesterone from the leftover follicle keeps the lining ready. With no pregnancy, progesterone and oestrogen fall and the lining breaks down as a period. Then FSH rises again and a new cycle starts. Gaps between periods differ between people.
FSH grows, oestrogen builds, a preovulatory rise can trigger LH release, and progesterone keeps the lining ready.
Original readings written for this topic. Videos from Cognito and TED-Ed; terms unknown.
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