FSH Stimulates Follicle Growth: FSH promotes the growth and development of follicles in the ovary.

Estrogen Production Begins: Granulosa cells produce estrogen by converting androgens from the theca cells using the enzyme aromatase.

Two-Cell, Two-Gonadotropin Interaction: LH stimulates theca cells to produce androgens, while FSH stimulates granulosa cells to convert these androgens into estrogen.

Rising Estrogen Levels: Estrogen increases as the dominant follicle grows, exerting negative feedback on FSH and LH secretion initially.

Estrogen Positive Feedback: Toward the end of the phase, high estrogen levels trigger a positive feedback loop, causing the LH surge.

Low Progesterone: Progesterone levels remain low as the corpus luteum has not yet formed.

Review: Uterus, Uterine Tubes & the Cervix (Physiology 2)