The follicular phase refers to the stage of follicular development and maturation in which the primordial follicle undergoes different stages of development as primary follicles, secondary follicles, and eventually becomes a mature follicle. Ovulation refers to the process when the follicle moves towards the surface of the ovary in response to the peak of luteinizing secretion, the follicular wall ruptures, the ovulatory orifice appears, and the oocyte is expelled with the zona pellucida, the corona radiata, and the oocyte fluid, a process called ovulation. The ovulated oocyte is captured by the fallopian tube and sent into the fallopian tube. After ovulation, the body enters the luteal phase, where the remnant follicular wall invaginates and blood enters the follicular cavity and coagulates to form a hematopoietic body. As the blood is absorbed, the granulosa cells and endometrial cells proliferate and luteinize, forming a yellow-appearing corpus luteum. If the egg is successfully fertilized, the embryo secretes HCG to continue the development of the corpus luteum into the corpus luteum of pregnancy.