BiologyISC Class 12 · Human Reproduction

Menstrual Cycle and Its Hormonal Control: ISC Class 12 Biology

Updated 15 October 2026 · Fact-checked

The menstrual cycle is the roughly 28/29-day reproductive cycle of female primates. It has menstrual, follicular, ovulatory and luteal phases. FSH and LH from the pituitary grow the follicle, the LH surge causes ovulation, oestrogen rebuilds the endometrium and progesterone from the corpus luteum maintains it.

Understand Menstrual Cycle and Hormonal Control

What it is. The reproductive cycle of female primates (monkeys, apes, humans) is the menstrual cycle. The first menstruation at puberty is menarche; cycles stop at about 50 years at menopause. In humans menstruation recurs on average every 28/29 days, and one ovum is released in the middle of each cycle. Regular cycles indicate a normal reproductive phase between menarche and menopause.

Two organs change in step: the ovary (follicle → corpus luteum) and the uterus (endometrium breaks down → regenerates → becomes secretory). Hormones from the anterior pituitary (FSH, LH) and the ovary (oestrogen, progesterone) link them.

Phases (28-day cycle).
1. Menstrual phase (days 1 to about 5; flow lasts 3-5 days): the endometrial lining and its blood vessels break down and the liquid leaves through the vagina. Menstruation happens only if the released ovum was not fertilised. Lack of menstruation may indicate pregnancy, but stress or poor health can also cause it.
2. Follicular (proliferative) phase (about days 5-13): FSH and LH rise gradually; primary follicles grow into a mature Graafian follicle, and the growing follicles secrete oestrogen. Oestrogen makes the endometrium regenerate by proliferation.
3. Ovulatory phase (about day 14): LH and FSH both peak in mid-cycle. The rapid rise of LH to its maximum, the LH surge, induces rupture of the Graafian follicle and release of the secondary oocyte: ovulation.
4. Luteal (secretory) phase (about days 15-28): the remaining parts of the Graafian follicle become the corpus luteum, which secretes large amounts of progesterone. Progesterone maintains the endometrium, which becomes thick, glandular and well supplied with blood, and its glands secrete fluid: a state needed for implantation.

Called luteal because of the corpus luteum, and secretory because the endometrial glands secrete actively under progesterone.

5. If no fertilisation: the corpus luteum degenerates, progesterone falls, the endometrium disintegrates, and menstruation starts a new cycle.
6. If pregnancy occurs: all events of the cycle stop and there is no menstruation; the corpus luteum keeps secreting progesterone.

Hormone summary.

Hormone	Source	Main action in the cycle
FSH	anterior pituitary	growth of follicles; with LH, oestrogen secretion
LH	anterior pituitary	LH surge → ovulation; formation of corpus luteum
Oestrogen	growing follicles	proliferation of the endometrium
Progesterone	corpus luteum	maintains the endometrium; secretory changes

FSH and LH are pituitary (gonadotropic) hormones; oestrogen and progesterone are ovarian hormones. ISC examiners penalise mixing these up.

Flow chart: FSH ↑ → follicle grows → oestrogen ↑ → endometrium proliferates → LH surge → ovulation → corpus luteum → progesterone ↑ → secretory endometrium → (no fertilisation) corpus luteum degenerates → progesterone ↓ → menstruation.

Oestrous versus menstrual cycle.

	Oestrous cycle	Menstrual cycle
Found in	non-primate mammals (cow, dog, rat)	primates (monkeys, apes, humans)
Receptivity	only during oestrus ('heat')	throughout the cycle
Bleeding	no menstrual bleeding; endometrium is reabsorbed	endometrium shed with bleeding

Draw and label: events of a 28-day cycle. Checklist: x-axis days 1-28; four rows: (1) pituitary hormones, LH and FSH curves with the LH peak at day 14; (2) ovarian events, growing follicle → Graafian follicle → ovulation → corpus luteum → degeneration; (3) ovarian hormones, oestrogen rising before ovulation and progesterone high in the luteal phase; (4) endometrium, thin at menstruation, thickening, thickest and secretory in the luteal phase; phase names along the top.

Menstrual Cycle and Hormonal Control: key facts

Phases of a 28-day cycle: $menstrual (1-5) \to follicular (5-13) \to ovulatory (\approx 14) \to luteal (15-28)$; Days are approximate; menstrual flow lasts 3-5 days.
Trigger of ovulation: $LH surge (mid-cycle) \to rupture of Graafian follicle \to ovulation$; FSH also peaks at mid-cycle.
Ovulation day in longer or shorter cycles: $ovulation day \approx cycle length - 14$; Use only when a question states that the luteal phase lasts about 14 days.
Hormone to tissue: $oestrogen \to proliferation; progesterone \to maintenance and secretion$; Fall in progesterone → menstruation.

How to answer Menstrual Cycle and Hormonal Control questions

ISC asks reasons ('why luteal and secretory'), roles of named hormones, phase identification from a graph or a day number, and oestrous-menstrual comparisons.

1Locate the day: 1-5 menstrual, 5-13 follicular, about 14 ovulation, 15-28 luteal (for a 28-day cycle).
2For each phase, describe the ovary and the uterus together, then name the hormone responsible.
3Keep sources straight: FSH and LH from the anterior pituitary; oestrogen from follicles; progesterone from the corpus luteum.
4For 'give reason' items, write both halves of a double name (luteal: corpus luteum; secretory: endometrial glands secrete).
5For graphs, identify LH by its sharp mid-cycle peak, oestrogen by its rise before ovulation and progesterone by its luteal plateau.
6For longer cycles, if told the luteal phase is fixed at about 14 days, subtract 14 from the cycle length to estimate ovulation.

Menstrual Cycle and Hormonal Control in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Missed periods and their causes

Suppose a Class 12 student preparing for board examinations, under heavy stress and skipping meals, misses her period for a month. Her friend insists that a missed period always means pregnancy.

Explain why the friend is wrong and what normally keeps the cycle running.

Try it first, then show the solutionSolution

Menstruation occurs when the corpus luteum degenerates, progesterone falls and the endometrium breaks down; this depends on a normal rhythm of FSH, LH, oestrogen and progesterone.
Pregnancy stops the cycle because the corpus luteum persists, but it is not the only cause.
Stress and poor health can disturb the hormonal rhythm, delaying follicle growth, ovulation and the following menstruation.
So lack of menstruation may indicate pregnancy, but it can also be caused by stress or poor health; a doctor should be consulted if it continues.

Answer: A missed period can result from stress or poor health disturbing the pituitary-ovarian hormones, not only from pregnancy.

Memory hook: The cycle is a hormone relay; stress can drop the baton.

Tricks to remember Menstrual Cycle and Hormonal Control

Short memory aids. Say each one aloud once, then use it on a question the same day.

M-F-O-L
My Friend Often Laughs: Menstrual, Follicular, Ovulatory, Luteal.
Use it when: Order of phases.
Follicle makes Oestrogen; Luteum makes Progesterone
F-O before ovulation, L-P after: 'FO then LP'.
Use it when: Which ovarian hormone dominates which half.
LH = Let Her (egg) out
The LH surge lets the egg out of the Graafian follicle.
Use it when: Linking LH to ovulation, not FSH.

Menstrual Cycle and Hormonal Control: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Luteal and secretory · 2 marks · Short answerBoard level

The phase that follows ovulation carries two names, luteal and secretory. Explain what each name refers to. (ISC asked for this reason in 2024.)

Try it first, then show the solutionSolution

Luteal: after ovulation the remains of the Graafian follicle form the corpus luteum (under LH), which dominates this phase by secreting progesterone (1 mark).
Secretory: under progesterone the endometrium becomes thick and glandular and its glands actively secrete fluid, preparing it for implantation (1 mark).

Answer: Luteal from the corpus luteum; secretory from the secreting endometrial glands under progesterone.

Example 2: Oestrous versus menstrual · 3 marks · Short answerBoard level

Give three differences between the oestrous cycle and the menstrual cycle.

Try it first, then show the solutionSolution

Oestrous: non-primate mammals (cow, dog); menstrual: primates including humans (1 mark).
Oestrous: female receptive only during oestrus (heat); menstrual: receptive throughout (1 mark).
Oestrous: no bleeding, endometrium reabsorbed; menstrual: endometrium shed with bleeding (1 mark).

Answer: Animals, receptivity and bleeding differ, as above.

Example 3: Reading a day · 3 marks · Short answerHarder board level

In a 28-day cycle, state the condition of the ovary, the endometrium and the dominant ovarian hormone on (a) day 9, (b) day 23.

Try it first, then show the solutionSolution

(a) Day 9, follicular phase: a follicle is growing towards a Graafian follicle (½); the endometrium is regenerating by proliferation (½); oestrogen from the follicle is rising (½).
(b) Day 23, luteal phase: a corpus luteum is present (½); the endometrium is thick, vascular and secretory (½); progesterone is high (½).

Answer: Day 9: growing follicle, proliferating endometrium, oestrogen. Day 23: corpus luteum, secretory endometrium, progesterone.

Example 4: Why menstruation follows · 3 marks · Short answerHarder board level

Explain the sequence of hormonal events that leads to menstruation when the ovum is not fertilised, and why menstruation does not occur during pregnancy.

Try it first, then show the solutionSolution

Without fertilisation, the corpus luteum degenerates near the end of the luteal phase (1 mark).
Progesterone secretion falls, so the endometrium can no longer be maintained; it disintegrates with its blood vessels, giving menstrual flow (1 mark).
In pregnancy the corpus luteum persists and progesterone stays high, so the endometrium is maintained and all events of the cycle stop (1 mark).

Answer: Corpus luteum degenerates → progesterone falls → endometrium breaks down; in pregnancy progesterone stays high.

Example 5: Pituitary or ovarian? · 2 marks · Short answerHarder board level

Classify FSH, LH, oestrogen and progesterone as pituitary or ovarian hormones, and give one action of each in the menstrual cycle.

Try it first, then show the solutionSolution

Pituitary (gonadotropins): FSH, growth of follicles; LH, the mid-cycle surge causes ovulation and forms the corpus luteum (1 mark).
Ovarian: oestrogen (from growing follicles), proliferation of the endometrium; progesterone (from corpus luteum), maintains the endometrium (1 mark).

Answer: FSH, LH: pituitary. Oestrogen, progesterone: ovarian. Actions as above.

Example 6: A 35-day cycle · 3 marks · Short answerHOTS / competency

Suppose a woman with regular 35-day cycles starts her period on 10 June. Assume that in every cycle the luteal phase lasts about 14 days. (a) On about which date does she ovulate? (b) Which hormone peaks on that day? (c) If the egg is not fertilised, on what date does her next period begin, and what hormonal change causes it?

Try it first, then show the solutionSolution

(a) Ovulation day ≈ 35 − 14 = day 21 of the cycle; day 1 is 10 June, so day 21 is 30 June (1 mark).
(b) LH (the LH surge), with FSH also at its peak (1 mark).
(c) The next cycle begins on day 36: 10 June + 35 days = 15 July. The corpus luteum degenerates and progesterone falls, so the endometrium breaks down (1 mark).

Answer: (a) About 30 June. (b) LH surge. (c) 15 July, triggered by the fall in progesterone as the corpus luteum degenerates.

Where students lose marks in Menstrual Cycle and Hormonal Control

The slips examiners see most often, and what to write instead.

Mistake: Swapping the roles of LH and FSH
In 2024 examiners reported that candidates confused the functions of LH and FSH when explaining the luteal phase.
Wrong working
FSH causes ovulation and forms the corpus luteum.
Right working
The LH surge causes ovulation; LH converts the ruptured follicle into the corpus luteum. FSH stimulates follicle growth.
Do this: LH = ovulation and luteum; FSH = follicle growth.
Usually costs: 1 mark.
Mistake: Calling pituitary hormones ovarian hormones
In 2025 examiners noted that candidates named oxytocin, FSH and LH as ovarian hormones.
Do this: Ovarian hormones: oestrogen, progesterone (and relaxin). FSH, LH and oxytocin are pituitary hormones.
Usually costs: Up to 2 marks.
Mistake: Giving only one half of a double name
Students explain 'luteal' and forget 'secretory'.
Do this: Write a sentence for each name: luteal (corpus luteum) and secretory (endometrial glands secrete).
Usually costs: 1 mark.
Mistake: Saying menstruation is caused by ovulation
Students link bleeding to the release of the egg.
Do this: Menstruation is caused by the fall in progesterone when the corpus luteum degenerates.
Usually costs: 1 mark.

Exam tips

Describe each phase under two headings, ovary and uterus, with the hormone named.
Use NCERT numbers: cycle about 28/29 days, flow 3-5 days, LH and FSH peak about day 14, menopause about 50 years.
Write 'LH surge' explicitly for ovulation.
In comparisons with the oestrous cycle, give examples of animals on each side.
Practise sketching the four-row cycle diagram; it earns marks in long answers.

Practice questions on Menstrual Cycle and Hormonal Control

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
The rupture of the Graafian follicle is induced by:
(a) a fall in progesterone (b) the LH surge (c) a rise in progesterone (d) a fall in FSH
Hint
Mid-cycle peak.
Answer
(b) The LH surge.
Q2 · 2 marks · Short answerBoard level
Define menarche and menopause and give the approximate age of menopause.
Hint
First and last.
Answer
Menarche is the first menstruation, at puberty. Menopause is the permanent stopping of menstrual cycles, at about 50 years of age.
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): The endometrium is thickest and most secretory in the luteal phase.
Reason (R): Oestrogen secreted by the corpus luteum is the main hormone of the luteal phase.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Which hormone does the corpus luteum secrete in large amounts?
Answer
(c). The corpus luteum secretes large amounts of progesterone, which maintains the secretory endometrium.
Q4 · 3 marks · Short answerHarder board level
Describe the changes in the ovary and the uterus during the follicular phase, naming the hormones involved.
Hint
Two organs, three hormones.
Answer
Ovary: under gradually rising FSH and LH, primary follicles grow into a mature Graafian follicle; the growing follicles secrete oestrogen. Uterus: oestrogen causes the endometrium to regenerate by proliferation after menstruation.
Q5 · 2 marks · Short answerHarder board level
On a hormone graph of one cycle, curve P shows a single sharp, narrow peak at mid-cycle; curve Q climbs through the first half and drops just after mid-cycle; curve R stays low in the first half and forms a broad plateau in the second half before falling. Identify P, Q and R and the gland or structure secreting each.
Hint
Surge; follicular rise; luteal plateau.
Answer
P: LH (the LH surge), anterior pituitary. Q: oestrogen, secreted by the growing follicles. R: progesterone, secreted by the corpus luteum.
Q6 · 2 marks · Short answerHarder board level
Why is progesterone sometimes called the 'pregnancy-maintaining hormone'? What happens to the endometrium if its level falls?
Hint
Maintenance of the lining.
Answer
Progesterone, secreted in large amounts by the corpus luteum, maintains the endometrium in the thick, secretory state needed for implantation and the events of pregnancy. If it falls, the endometrium disintegrates and menstruation follows.
Q7 · 2 marks · Short answerHOTS / competency
Suppose the corpus luteum of a woman remains active for 10 days longer than usual in a cycle without fertilisation. Predict and explain the effect on (a) the timing of menstruation, (b) the state of the endometrium in that period.
Hint
Menstruation follows the fall of progesterone.
Answer
(a) Menstruation is delayed by about 10 days, because it begins only when the corpus luteum degenerates and progesterone falls. (b) The endometrium stays thick and secretory because progesterone keeps maintaining it.
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose a farmer notices that his cow accepts the bull only for a short time every three weeks and shows no bleeding, whereas a female monkey in a zoo has a monthly bleeding but no fixed mating season.
(a) Name the reproductive cycle of each. (1)
(b) Give one difference shown in the passage and one not shown. (1)
(c) What happens to the endometrium of the cow at the end of a cycle without pregnancy? (1)
Hint
Heat; bleeding.
Answer
(a) Cow: oestrous cycle; monkey: menstrual cycle. (b) Shown: receptive only during oestrus (heat) versus receptive throughout; or bleeding absent versus present. Not shown: found in non-primate mammals versus primates. (c) It is reabsorbed, not shed.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is the average length of the human menstrual cycle?Show answer
About 28/29 days.
2.What is the LH surge?Show answer
The rapid mid-cycle rise of LH to its peak, which induces ovulation.
3.Which structure secretes large amounts of progesterone?Show answer
The corpus luteum.
4.Which hormone makes the endometrium proliferate?Show answer
Oestrogen.
5.Name two animals with an oestrous cycle.Show answer
Cow, dog (or rat, horse).
6.What happens to the cycle during pregnancy?Show answer
All events of the menstrual cycle stop and there is no menstruation.

Menstrual Cycle and Hormonal Control: frequently asked questions

What are the phases of the menstrual cycle?

Menstrual, follicular (proliferative), ovulatory and luteal (secretory).

Which hormone causes ovulation?

The mid-cycle surge of LH from the anterior pituitary.

Why does menstruation occur?

If the ovum is not fertilised, the corpus luteum degenerates, progesterone falls and the endometrium breaks down.

How is the oestrous cycle different from the menstrual cycle?

It occurs in non-primate mammals, the female is receptive only in heat, and there is no bleeding because the endometrium is reabsorbed.

What is the role of progesterone in the cycle?

It maintains the thick, secretory endometrium needed for implantation and pregnancy.