The conversion of the residual follicle into the corpus luteum is triggered by a surge of which hormone?

• A. LH
• B. FSH
• C. Estrogen
• D. Progesterone

Answer: (A)

The main idea is that the surge of luteinizing hormone acts as the signal to transform the remaining follicle into the corpus luteum. When LH peaks mid-cycle, it prompts ovulation and triggers the luteinization process, where the granulosa and theca cells of the ruptured follicle reorganize into luteal cells that secrete progesterone (with some estrogen) to support a potential pregnancy. Follicle-stimulating hormone mainly supports the growth of follicles earlier in the cycle and does not drive this luteal transformation. Estrogen is elevated before ovulation and helps stimulate the LH surge, but it is not the trigger for converting the follicle into the corpus luteum. Progesterone is produced after the corpus luteum forms, serving to maintain the endometrium if implantation occurs, rather than initiating luteinization.