Which structure is responsible for producing oestrogen during follicular development?

• A. Corpus luteum
• B. Ovaries
• C. Hypothalamus
• D. Follicles

Answer: (D)

Estrogen production during follicular development comes from the developing ovarian follicles themselves, mainly within the granulosa cells of those follicles. As the follicle grows, FSH stimulates the granulosa cells, and the theca interna cells nearby produce androgens. The granulosa cells use the enzyme aromatase to convert these androgens into estrogen (primarily estradiol). This rise in estrogen helps drive follicle growth and prepares the uterus for possible implantation, while also providing feedback to regulate gonadotropin release. After ovulation, estrogen production shifts largely to the corpus luteum, which then primarily secretes progesterone. The hypothalamus regulates the release of hormones but does not produce estrogen directly, and while the ovaries overall produce estrogen, the site responsible during follicular development is the follicles themselves.