Hormonal Control of the Menstrual Cycle and LH Surge
Biology · Human Reproduction · NEET
Four hormones run the menstrual cycle. GnRH from the hypothalamus tells the pituitary to release FSH and LH; FSH and LH rise slowly in the follicular phase and make the follicle grow and release oestrogen. Both FSH and LH peak near day 14, and the sudden sharp rise of LH (the LH surge) bursts the Graafian follicle to cause ovulation. Memory hook: "GnRH → FSH+LH → oestrogen up → LH SURGE bursts the egg out."
FSH and LH rise through the follicular phase; high oestrogen from the mature follicle triggers the mid-cycle LH surge (day 14) that causes ovulation. After ovulation, progesterone from the corpus luteum rises while FSH and LH stay low in the luteal phase.
Your doubts, answered
Which hormone actually causes ovulation, FSH or LH?
LH causes ovulation. The rapid rise of LH to its maximum at mid-cycle, called the LH surge, ruptures the mature Graafian follicle and releases the ovum. FSH helps the follicle grow earlier in the cycle, but the final trigger for ovulation is the LH surge, not FSH.
What exactly is the LH surge?
The LH surge is a sudden, sharp increase of luteinising hormone (LH) to its highest level around the 14th day of the cycle. High oestrogen from the mature follicle triggers this surge. The surge makes the Graafian follicle burst, so the ovum is released. This is the single most important event NEET asks about.
Do FSH and LH increase or decrease during the follicular phase?
They INCREASE gradually during the follicular phase. This is a common NEET trap. The gonadotropins FSH and LH rise slowly through the follicular phase, stimulate follicle growth and oestrogen secretion, and then peak in the middle of the cycle. Any statement saying they 'decrease during the follicular phase' is incorrect.
Which hormone is highest around day 14?
LH is the standout hormone at mid-cycle because of the LH surge, and FSH also reaches a peak. Oestrogen from the mature follicle is also high just before day 14 and is the trigger that sets off the LH surge. So at mid-cycle: oestrogen high, then LH and FSH peak, then ovulation.
Why are FSH and LH low in the luteal phase?
After ovulation the corpus luteum forms and secretes large amounts of progesterone. Progesterone suppresses the release of FSH and LH, so both stay low in the luteal phase. Because FSH (which grows follicles) is low, no new follicles develop until the corpus luteum degenerates and the next cycle begins.
What does oestrogen do versus progesterone in the cycle?
Oestrogen is secreted by the growing follicles in the follicular phase; it helps rebuild the endometrium and its peak triggers the LH surge. Progesterone is secreted by the corpus luteum in the luteal phase; it maintains the thick endometrium so a fertilised ovum can implant.
⚠️ The NEET trap ✗ LH and FSH decrease gradually during the follicular phase. ✓ LH and FSH INCREASE gradually during the follicular phase and peak at mid-cycle; the LH surge then causes ovulation. 🧠 NEET flips 'increase' to 'decrease' for the follicular phase. Gonadotropins RISE, they never fall in the follicular phase. Read the direction word carefully.
Real NEET questions
NEET 2016 / 2019
Select the incorrect statement:
A · FSH stimulates the Sertoli cells which help in spermiogenesis
B · LH triggers ovulation in ovary
C · LH and FSH decrease gradually during the follicular phase ✓
D · LH triggers secretion of androgens from the Leydig cells
Solution: During the follicular phase the gonadotropins LH and FSH actually INCREASE gradually and peak at mid-cycle, so option C is the incorrect statement. The other three are correct: FSH acts on Sertoli cells, LH triggers ovulation, and LH stimulates androgen secretion from Leydig cells.
NEET 2020
Which of the following hormone levels will cause release of ovum (ovulation) from the Graafian follicle?
A · Low concentration of LH
B · Low concentration of FSH
C · High concentration of Estrogen ✓
D · High concentration of progesterone
Solution: Ovulation is linked to HIGH mid-cycle levels, not low ones. The growing follicle secretes high oestrogen at mid-cycle, and this high oestrogen triggers the LH surge that ruptures the Graafian follicle. Low LH, low FSH, or high progesterone do not cause ovulation, so high oestrogen is the answer.
NEET 2019
No new follicles develop in the luteal phase of the menstrual cycle because
A · Follicles do not remain in the ovary after ovulation
B · FSH levels are high in the luteal phase
C · LH levels are high in the luteal phase
D · Both FSH and LH levels are low in the luteal phase ✓
Solution: In the luteal phase the corpus luteum secretes large amounts of progesterone, which suppresses gonadotropin release, keeping both FSH and LH low. Since FSH (which drives follicle growth) is low, no new follicles can develop during the luteal phase.
Solved Human Reproduction NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What are the four main hormones of the menstrual cycle?
FSH and LH from the anterior pituitary (both controlled by GnRH from the hypothalamus), oestrogen from the growing follicles, and progesterone from the corpus luteum.
On which day does the LH surge occur?
Around day 14 (the middle of a 28-day cycle). Both LH and FSH peak here, but the sharp LH surge is what causes ovulation.
Which hormone maintains the endometrium after ovulation?
Progesterone, secreted by the corpus luteum during the luteal phase, maintains the thick endometrium needed for implantation.
What triggers the LH surge?
The high level of oestrogen released by the mature Graafian follicle just before mid-cycle triggers the LH surge.
What happens to the hormones if the ovum is not fertilised?
The corpus luteum degenerates, so progesterone falls. The endometrium then breaks down, causing menstruation and the start of a new cycle.
