Menstrual Cycle
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Direct answer
The menstrual cycle is the monthly reproductive cycle of human females, averaging 28 days, that begins at puberty with menarche and ceases around the age of fifty at menopause. Each cycle runs through the menstrual phase, when the endometrium breaks down and is shed, the proliferative or follicular phase, when estrogen from a growing ovarian follicle rebuilds the uterine lining, ovulation at about the fourteenth day triggered by a sharp luteinising hormone surge, and the secretory or luteal phase, when corpus luteum progesterone maintains the endometrium for possible implantation.
What you must remember
- Pituitary control: FSH stimulates the growth of ovarian follicles, whose rising estrogen output regrows the endometrium during the proliferative phase.
- The LH surge: a rapid rise in luteinising hormone at about mid-cycle — the fourteenth day of a 28-day cycle — ruptures the Graafian follicle and releases the ovum.
- Corpus luteum: the ruptured follicle converts into the corpus luteum, whose progesterone completes the endometrium, makes it ready for implantation and maintains early pregnancy.
- Phase naming: the same weeks carry ovarian names (follicular and luteal) and uterine names (proliferative and secretory), paired one to one.
- Menstrual flow: if fertilisation does not occur, the corpus luteum regresses, progesterone falls, and the endometrial lining with blood is shed through the vagina for about five days.
- On fertilisation: the blastocyst embeds in the endometrium, and the placenta takes over hormone production with human chorionic gonadotropin (hCG) and human placental lactogen (hPL) sustaining the corpus luteum and pregnancy.
- Cyclical changes also occur in the ovary (follicular growth, ovulation, corpus luteum formation) and are used clinically to time fertility-window counselling — the basis of natural family planning.
Common confusion
Students mix the two naming systems: proliferative equals follicular (estrogen-dominated, before ovulation) and secretory equals luteal (progesterone-dominated, after ovulation). The hormones' roles are also swapped in haste — FSH grows the follicle, LH triggers ovulation, and progesterone, not estrogen, is the pregnancy-maintaining hormone of the luteal phase.
Exam-focused takeaway
NEET-UG asks which hormone surges before ovulation, which hormone maintains the endometrium, and what degenerates when pregnancy does not occur. Assertion-reason stems test the pituitary-ovarian-uterine axis across the cycle, and statement-based questions pair phase names with their dominant hormones. Timeline facts — ovulation on about the fourteenth day of a 28-day cycle, cycle length averaging 28 days, menarche at puberty and menopause near fifty — supply direct one-liners almost every year.
Frequently asked questions
Which hormone triggers ovulation?
A rapid surge of luteinising hormone (LH) from the anterior pituitary at about mid-cycle, on roughly the fourteenth day of a 28-day cycle.
What happens during the luteal phase?
The ruptured follicle becomes the corpus luteum and secretes progesterone, which makes the endometrium secretory and ready for implantation.
What is the difference between menarche and menopause?
Menarche is the first menstrual flow at puberty marking the start of reproductive life; menopause is the permanent cessation of cycles around the age of fifty.
Which hormone maintains early pregnancy?
Progesterone from the corpus luteum, later sustained by placental hCG once implantation has occurred.
Why does menstruation occur?
Because the unfertilised ovum means the corpus luteum degenerates, progesterone support is withdrawn, and the thickened endometrium breaks down and is discharged.