Endocrinology

At the beginning of the follicular phase, FSH and LH levels are increased relative to baseline. Estrogen and progesterone levels are low.

Follicular Development

Increased FSH levels stimulate 15-20 primordial follicles to develop into primary unilaminar follicles.

Uterine Endometrial Cycle

Menstruation occurs at the beginning of the follicular phase and the functionalis is shed.