Endocrinology

One day before ovulation, a surge in LH occurs and FSH levels increase temporarily. LH and FSH both increase due to positive feedback by estrogen at the level of the pituitary gland. LH and FSH begin to decrease back to baseline levels almost immediately. By the time ovulation occurs, LH and FSH are on the decline.

 Follicular Development

Before ovulation occurs, one follicle evolves into a dominant follicle and develops an antrum while the remaining primary follicles undergo atresia. The dominant follicle, now called a Graafian follicle, completes its first meiotic division. At ovulation, the secondary oocyte and corona radiata are expelled into the peritoneal cavity and taken up by the oviduct.

 Uterine Endometrial Cycle

At ovulation, the functionalis and endometrial glands have reached their maximum sizes. The endometrial glands are still non-secretory.