GCSE · Biology · Edexcel · Spec 1BI0

Stages of the menstrual cycle

Picture laying the table for a guest who may not come, clearing it away, then laying it again. The menstrual cycle does exactly that with the uterus lining.

Biology · The menstrual cycle

Rebuild the cycle, then break it

2 stages are missing. Use the rest of the loop to work out which goes where.

Stage 2: The lining regrows
The uterus lining thickens again.
Stage 4: Egg not fertilised
No embryo implants, so the thick lining isn't needed — and the loop heads back to stage 1.

…and stage 4 leads back to stage 1.

Exam line: Menstruation is the uterus lining breaking down. Ovulation is an egg being released from an ovary. Two different stages — never swap them.

Two hormones, one lining

OestrogenvsProgesterone

Both hormones act on the same thing — the uterus lining. The difference is what they do to it.

Focus

What it does to the uterus lining

Oestrogen

Makes it thicken — it builds the lining up

Progesterone

Maintains it — it keeps the lining ready

The insight

Build versus keep. If you remember one difference between these two hormones, make it this one.

What it is getting the lining ready for

Oestrogen

Ovulation: the lining has regrown by the time an egg is released

Progesterone

Implantation: a fertilised egg embedding in the lining

The change in the cycle it is linked to

Oestrogen

The lining regrowing after menstruation

Progesterone

Menstruation — when progesterone falls, the lining breaks down

How hormones get the message through

Reason it through

How can a hormone made in one part of the body change the uterus somewhere else?

Link 1 of 4

First link · your turn

Where are the hormones that control the cycle made?

Locked — reveal the link above first

Biology · The cycle across a lifetime

Running, paused or not running?

What is each person's menstrual cycle doing right now?

Still to sort

Running (0)

The loop is going round, roughly every 28 days.

Paused (0)

On hold: no ovulation and no breakdown of the lining.

Where the line is: Paused, not stopped — it is hormone changes during pregnancy that put the cycle on hold.

Not running (0)

It hasn't started yet, or it has stopped at the menopause.

Where the line is: Not running is about the start and end of the cycle in a lifetime: puberty and the menopause.

4 of 4 still to sort.

The loop doesn't run from birth to old age. Sort each person by what their cycle is doing right now.

Watch out: Paused and not running are different. A pause happens during pregnancy; not running means the cycle hasn't started yet or has stopped at the menopause.

Check your thinking

Only one of these is right. Which?

Sam's revision notes on the menstrual cycle have four lines in them. Three of them hide a mistake.

Which line would you sign off as correct?

Menstruation is when the egg is released.Every menstrual cycle is exactly 28 days long.Hormones in the blood affect every organ they reach.Ovulation is when an egg is released from an ovary.

How sure are you?

I'm sureI think soI'm guessing

Menstruation is when the egg is released.

This is a common misconception

This is the classic mix-up. Menstruation is the uterus lining breaking down and leaving the body. The egg is released at ovulation — a separate stage that comes after the lining has regrown.

Every menstrual cycle is exactly 28 days long.

This is a common misconception

28 days is the number used to model the cycle, and it is about right. But it is approximate: cycle length differs between people. Treat 28 as the model, not a rule.

Hormones in the blood affect every organ they reach.

This is a common misconception

Half right. The blood does carry hormones to every organ. But only target organs respond, because only their cells have receptors complementary in shape to the hormone.

Ovulation is when an egg is released from an ovary.

This matches the evidence

Correct. Notice that it is a different event from menstruation, which is the lining breaking down. Open the other three lines too — each one is a mistake worth knowing.

Menstruation is the lining; ovulation is the egg. 28 days is a model, not a rule. And a hormone only acts where the matching receptors are.

Put it in writing

Write it, then mark it

During the menstrual cycle, the uterus lining thickens, is kept ready, and then breaks down. Explain how oestrogen and progesterone cause these changes. [4 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Oestrogen causes the uterus lining to thicken. (1 mark)
Progesterone maintains the lining (keeps it ready). (1 mark)
The lining is kept ready for a fertilised egg to implant. (1 mark)
A fall in progesterone causes the lining to break down (menstruation). (1 mark)

Model answer

Oestrogen, which is secreted by the ovaries, makes the uterus lining thicken. Progesterone maintains the lining, keeping it ready in case a fertilised egg implants. When the level of progesterone falls, the lining breaks down and leaves the body — this is menstruation.

Name the hormone AND what it does, every time: oestrogen thickens, progesterone maintains, and a fall in progesterone brings the lining down.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

A loop that goes round about every 28 days — and the one event that stops it.

What you need to know

The menstrual cycle is a repeating cycle that prepares the body for pregnancy. It is about 28 days long, but the length differs between people.
Menstruation is the breakdown of the uterus lining, which leaves the body. Ovulation is the release of an egg from an ovary.
Oestrogen makes the uterus lining thicken; progesterone maintains it for implantation, and a fall in progesterone causes menstruation.
If the egg is not fertilised, the lining breaks down and the cycle repeats. If an embryo implants in the lining, the cycle stops.

The big picture

The menstrual cycle is a loop of about 28 days that prepares the body for pregnancy. The uterus lining breaks down (menstruation), regrows, and an egg is released (ovulation). If the egg is not fertilised, the lining breaks down again and the loop repeats; if an embryo implants, the cycle stops. Oestrogen thickens the lining, progesterone maintains it, and a fall in progesterone causes menstruation.

Key points

1Order of stages: menstruation → the lining regrows → ovulation → (egg not fertilised) → menstruation again.

2An egg is fertilised in a fallopian tube; it can become a zygote, then an embryo that implants in the uterus lining.

3The cycle is controlled by sex hormones from the pituitary gland and the ovaries. They travel in the blood and act only on target cells with complementary receptors.

4The cycle begins at puberty, is paused during pregnancy, and stops at the menopause (around age 50) when sex hormone levels decrease.

.we-_R_18slubsnpfiv5ubrb_ [data-we-step]{display:flex !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-solution]{display:block !important}.we-_R_18slubsnpfiv5ubrb_ [data-we-reveal]{display:none !important}

Worked example

Problem

A woman is pregnant. Explain why she does not ovulate or menstruate while she is pregnant.

⚠ Watch out

Mixing up menstruation and ovulation. Menstruation is the uterus lining breaking down and leaving the body; ovulation is an egg being released from an ovary. They are two different stages of the cycle, not the same event.

🧠

Memory hook

Oestrogen builds, progesterone holds — and when progesterone drops, the lining drops.

✓

Check yourself

From memory, sketch the cycle as a four-stage loop. Mark where the egg is released, where the lining breaks down, and the one point where the loop can stop.

Flashcards

(14)

What is menstruation?

The breakdown of the uterus lining, which then leaves the body.

What is ovulation?

The release of an egg from an ovary.

About how long is one menstrual cycle?

About 28 days. It is often modelled as 28, but the length differs between people.

What does the menstrual cycle prepare the body for?

Pregnancy.

Which two parts of the body produce the hormones that control the cycle?

The pituitary gland and the ovaries.

What does oestrogen do to the uterus lining?

It makes the lining thicken. Oestrogen is secreted by the ovaries.

What does progesterone do to the uterus lining?

It maintains the lining, keeping it ready for a fertilised egg to implant.

What does a fall in progesterone cause?

Menstruation — the uterus lining breaks down.

How do hormones reach their target organs?

They are secreted into the blood and carried around the body.

Why does a hormone affect only its target organs?

Only cells with receptors complementary in shape to the hormone respond to it.

Where is an egg fertilised?

In a fallopian tube.

What happens to the cycle if an embryo implants in the uterus lining?

The cycle stops — the lining is not broken down.

When does the menstrual cycle start and stop in a lifetime?

It starts at puberty and stops at the menopause (around age 50, earlier or later for some), when sex hormone levels decrease.

What happens to ovulation and the breakdown of the lining during pregnancy?

Both stop: hormone changes during pregnancy pause the cycle.

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.

Learning with Lightbulb is opening soon

You can use this lesson now. Join the waitlist and we'll let you know when the full Lightbulb experience is ready.

Keep me posted

Rebuild the cycle, then break it

Running, paused or not running?

Only one of these is right. Which?

Write it, then mark it

More Edexcel GCSE Biology topics