40,000 oocytes After puberty each month a group of primary oocytes are stimulated to reach metaphase II just prior to ovulation. If sperm penetration occurs meiosis is completed. Other follicles degenerate forming atretic follicles. Estrogen levels fall. Only the stratum basalis remains.
Follicular cells secrete increasing amounts of estrogen.
Stratum basalis cells proliferate producing the s. functionalis. Short straight endometrial glands form, spiral arterioles regrow. Vascularization of the s. functionalis increases.