Ovulation is triggered by a sharp rise in
- A. oestrogen alone
- B. luteinising hormone
- C. progesterone
- D. follicle stimulating hormone
Explanation
Rising oestrogen from the ripening follicle switches the pituitary from negative to positive feedback and produces a sudden LH surge, which ruptures the follicle within about a day. Oestrogen is the signal that causes the surge rather than the trigger itself, which is why it is the tempting choice. Progesterone rises only after ovulation, once the corpus luteum has formed.