Human Reproduction

Hormonal regulation of the menstrual cycle is a key topic in NCERT Class 12, Chapter 3 (Human Reproduction). Around the fourteenth day of a typical cycle, rapidly rising oestrogen from the maturing follicle triggers a steep peak in luteinizing hormone known as the LH surge. This surge induces the mature Graafian follicle to rupture and release the secondary oocyte, the event called ovulation. Onset of menstrual bleeding is incorrect because menstruation is caused by a fall in progesterone and oestrogen when the corpus luteum degenerates, not by the LH peak. Thickening of the endometrium is driven mainly by oestrogen during the follicular phase and progesterone afterwards, so it is not a direct effect of the LH surge. Initiation of follicle growth is governed largely by follicle-stimulating hormone early in the cycle. A timing check confirms the answer: the mid-cycle LH surge coincides precisely with follicle rupture, making ovulation its most direct consequence.