Menstruation begins when
Correct answer: C. the corpus luteum degenerates and progesterone falls
- A. oestrogen rises sharply
- B. follicle stimulating hormone falls to zero
- C. the corpus luteum degenerates and progesterone falls
- D. the blastocyst implants in the uterine wall
Explanation
Without implantation the corpus luteum breaks down, progesterone withdrawal removes the support of the endometrium, its blood vessels constrict and the lining is shed as the menstrual flow. The falling progesterone also releases the pituitary from inhibition, so FSH rises again and the next cycle begins. Implantation has the opposite effect, since it keeps the corpus luteum alive and prevents menstruation.
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About Menstrual Cycle
The menstrual cycle covers the coordinated changes in the ovaries and uterus, including menstruation, follicular growth, ovulation and corpus luteum formation. It links follicle-stimulating hormone, luteinizing hormone, oestrogen and progesterone with endometrial changes, and distinguishes the ovarian cycle from the uterine cycle and the hormonal events of pregnancy.
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