KS3 · Biology
The human menstrual cycle
Imagine making up a spare room every month for a guest who might never come, then clearing it and starting again. Odd? That's roughly what the uterus does.
Where it all happens
Layers
Explore
tap a part ↓
Journey 2: when the lining breaks down, it leaves the uterus and passes out of the body through the vagina.
The whole cycle happens inside these five parts. Tap a part to see its job, and switch each journey on or off.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
Every month, the uterus gets ready for a guest who may never arrive. Then it clears up and starts again.
What you need to know
- The menstrual cycle happens in the adult female reproductive system: the ovaries, fallopian tubes, uterus, cervix and vagina.
- Its purpose: the uterus lining thickens to create the conditions a fertilised egg cell needs to develop and grow.
- Ovulation is the release of an egg cell from an ovary into a fallopian tube. Egg cells travel along the fallopian tubes towards the uterus, and fertilisation can take place in a fallopian tube.
- Menstruation (a period) is when the uterus lining breaks down and passes out of the body through the vagina, with the egg cell, if the egg cell has not been fertilised.
- In an average cycle: days 0 to 5, menstruation; days 6 to 14, the lining builds up again; around day 14, ovulation; the lining keeps thickening as the egg cell travels; days 20 to 28, the lining is maintained in case the egg cell has been fertilised.
- The average cycle is 28 days, but the length of the cycle and of its stages varies from person to person, and can vary for the same person.
- Hormones, which are chemical messengers, control the cycle. Their levels go up and down as it runs.
- The cycle begins at puberty (for most girls between 8 and 14), stops during pregnancy so the pregnancy can be maintained, and stops completely at the menopause (around age 50).
The big picture
The menstrual cycle is a monthly loop that prepares the uterus for a possible pregnancy. The uterus lining thickens so a fertilised egg cell could develop and grow. Around day 14 of an average 28-day cycle, an ovary releases an egg cell (ovulation), which travels along a fallopian tube, where it can be fertilised. If it is not, the lining breaks down and leaves through the vagina as a period (menstruation), and the loop starts again. Hormones control the cycle, its length varies, and it runs from puberty to the menopause, pausing in pregnancy.
Key points
Worked example
Problem
Jess's period starts on 1 March. If her cycle follows the average 28-day pattern, roughly when would you expect her to ovulate, and when would her next period be due? Why might the real dates be different?
⚠ Watch out
Mixing up ovulation and menstruation. Ovulation is an egg cell being released from an ovary; menstruation is the uterus lining breaking down and leaving the body through the vagina.
Memory hook
Shed, build, release, hold, and round again. The uterus is a room made ready for a guest who might not come: if nobody arrives, the room is cleared and set up again.
Check yourself
Close the page and sketch the cycle as a loop. Mark where ovulation sits, say what the lining is doing at each stage, and explain what changes if the egg cell is fertilised.
Flashcards
(14)Name the five parts of the adult female reproductive system where the menstrual cycle takes place.
What is ovulation?
What is menstruation?
Why does the uterus lining thicken each cycle?
What happens to the lining if the egg cell is not fertilised?
How long is the average menstrual cycle?
What controls the menstrual cycle?
In an average cycle, when does ovulation happen?
What happens to the uterus lining during days 6 to 14?
What happens to the uterus lining during days 20 to 28?
Where can an egg cell be fertilised?
When does the menstrual cycle begin?
What happens to the menstrual cycle during pregnancy, and why?
When does the menstrual cycle stop completely?
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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How this lesson was checked. This KS3 Biologylesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 1 October 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.