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Why does menstruation occur when the corpus luteum degenerates?

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Detailed cross-sectional illustration of a human ovary showing the stages of follicle development, ovulation, and corpus luteum formation, with labeled structures including primordial, primary, secondary, and mature follicles, a ruptured follicle releasing an ovum, and corpus luteum and albicans. An inset at the bottom shows the ovary's location in the female reproductive system. — ovary The steps of ovulation, beginning with a dormant primordial follicle that grows and matures and is eventually released from the ovary into the fallopian tube.

Menstruation occurs when the corpus luteum degenerates because of the resulting decline in hormone levels. During the luteal phase of the menstrual cycle, the corpus luteum produces large quantities of progesterone and some estrogen, which maintain the endometrium in preparation for a potential pregnancy.12

If fertilization does not occur, the corpus luteum becomes inactive and degenerates after approximately 10 to 14 days. This degeneration leads to a significant decrease in serum estrogen and progesterone concentrations. The drop in these hormones causes the constriction of uterine arteries, which interrupts the delivery of oxygen and nutrients to the endometrial lining. Consequently, the endometrium breaks down and is sloughed off, resulting in the vaginal bleeding known as menstruation.32145