Menstrual cycle sim
Drag the day slider through a 28-day cycle and watch the follicle, ovulation and corpus luteum on a model ovary, the uterus lining build up and shed, and oestrogen, progesterone, FSH and LH rise and fall on a live graph; then see what changes when the egg is fertilised or the combined pill is taken.
Reproduction in humans: the menstrual cycle and its hormones · covers the O-Level, IGCSE, GCSE topic
What the sim shows
The menstrual cycle: a model. Drag the slider along the 28-day track (day 1 is the first day of the period). The model ovary shows the follicle growing (days 1 to 13), ovulation on day 14 and the corpus luteum (days 15 to 28), at real size. The model block of the uterus wall shows the lining, drawn 3 times its real thickness: it is shed in the period, repaired and thickened by oestrogen from the follicle, then kept thick by progesterone from the corpus luteum. If no egg is fertilised, the corpus luteum breaks down, progesterone falls and the lining is shed again. If the egg is fertilised, the embryo implants (about day 21) and a hormone from it keeps progesterone high, so there is no period. FSH makes a follicle mature and LH causes ovulation (IGCSE Supplement and GCSE; switch them off for oestrogen and progesterone only). The combined pill's man-made oestrogen and progesterone stop FSH and LH being released, so no egg matures and none is released (O-Level: they stop eggs maturing) (the pill set-up: O-Level and GCSE; not on the current Cambridge IGCSE syllabus). The feedback links (oestrogen slows FSH and triggers the LH surge; progesterone stops FSH and LH) are GCSE Higher. Simplified on purpose: one ideal 28-day cycle with ovulation on day 14 (real cycles vary in length, and ovulation is about 14 days before the next period); the hormone levels are typical daily values (illustrative, ≈), and the tubes and graph show each as a % of its own peak in a normal cycle, so the four lines are not on the same scale; the fertile window uses about 5 days for sperm and about 1 day for the egg (some books give days 11 to 17: use the range your teacher gives); the pill set-up counts days of the pill pack, with a withdrawal bleed on days 24 to 27; the tube colours are a key (the hormones are colourless).
- Lit pointer: the day you have chosen
- Close-up: the hormone graph for the whole cycle, with the lining under it
- Dashed line: ovulation
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
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