GCSE · Biology · Edexcel · Spec 1BI0
Hormone interactions in menstrual cycle
Four chemical messages, one repeating loop, and no boss. The cleverest bit is how it ends, because the ending restarts everything. Can you rebuild it?
Where it all happens
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Tap a part to see what it makes or what acts on it.
Two glands and one target: the pituitary gland, the ovary with its follicle, and the uterus lining.
Tap a part to see what it makes or what acts on it. Switch the view to add the messages.
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
Four hormones, one loop, and no hormone in charge.
What you need to know
- Four hormones run the cycle: FSH, oestrogen, LH and progesterone, and each one switches the next on or off.
- FSH is secreted by the pituitary gland and causes a follicle in the ovary to mature.
- As the follicle matures, it secretes oestrogen.
Have a goMaya swears that FSH is made in the ovary and oestrogen comes from the pituitary. She sounds very sure. Is she right?
No. The pituitary secretes FSH, and the maturing follicle in the ovary secretes oestrogen.
FSH is the message sent out from the pituitary; oestrogen is secreted by the follicle once FSH has made it mature.
- Oestrogen thickens the uterus lining, triggers the secretion of LH and inhibits FSH.
- LH causes ovulation, which is the release of an egg from the mature follicle.
Have a goOestrogen or LH: which one is secreted first in the loop? Decide before you look.
Oestrogen.
Oestrogen triggers the secretion of LH, so LH is the result of that trigger and cannot start the chain.
- After ovulation the follicle breaks down and secretes progesterone.
- Progesterone maintains the uterus lining and inhibits FSH and LH.
Have a goOestrogen and progesterone both act on the uterus lining. What does each one do to it?
Oestrogen thickens the lining; progesterone maintains it.
They share a target but not a job: one makes the lining thicker, the other keeps it in place.
- When progesterone falls, the lining breaks down. That is menstruation, and the cycle begins again.
- The 28-day cycle is a model, and real cycles differ between people.
The big picture
Four hormones run the menstrual cycle by switching each other on and off. FSH matures a follicle, oestrogen thickens the uterus lining and triggers LH, LH causes ovulation, and progesterone maintains the lining. When progesterone falls, menstruation happens and the cycle begins again.
Key points
Worked example
Problem
Explain why menstruation starts. Build the answer one link at a time.
⚠ Watch out
Mixing up ovulation and menstruation. Ovulation is the release of an egg from the mature follicle, and LH causes it. Menstruation is the uterus lining breaking down after progesterone falls. FSH does not release the egg: it matures the follicle.
Memory hook
Pituitary sends, ovary replies. FSH and LH are the pituitary's messages; oestrogen and progesterone are the ovary's replies. And progesterone is the lining's protector: when the protector falls, the lining falls.
Check yourself
Cover the page and say it aloud: which hormone must fall for the next cycle to begin, what does that do to the lining, and which hormone is then free again?
Flashcards
(12)Which gland secretes FSH and LH?
What does FSH do?
What does the maturing follicle secrete?
Name the three things oestrogen does in the cycle.
What does LH cause?
What happens to the follicle after ovulation?
What does progesterone do to the lining, and to FSH and LH?
Which hormone must fall before menstruation can start?
What is menstruation?
Which hormone is the only one in this loop that causes ovulation?
Which two hormones are made in the pituitary, and which two in the ovary?
How should you read the 28 days in the textbook 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.
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