Under the regulation of the pituitary hormones, luteinizing hormone (LH) and follicle stimulating hormone (FSH), follicles develop within the ovary. Primordial, primary, and secondary follicles contain an oocyte that is suspended in prophase of the first meiotic division. Growth in these follicles is due to an increase in the number of granulosa cells. Secondary follicles develop an antrum that contains the secretions of the granulosa cells. Within the mature follicle, the first meiotic division is completed. A sharp increase in the LH level stimulates ovulation. After ovulation, the remaining granulosa cells and surrounding cells form a corpus luteum. If pregnancy occurs, the corpus luteum is maintained. If pregnancy does not occur, the corpus luteum slowly degenerates to form a corpus albicans.