After ovulation, in the luteal phase, within 2-3 days the remaining follicular or granulosa cells give rise to the corpus luteum. The luteinized cells of the corpus luteum (granulosa lutein cells and theca lutein cells) mainly secrete progesterone, but they also secrete some oestrogen. Progesterone prevents the development of other tertiary follicles. If the female becomes pregnant, the corpus luteum develops further up to about 3 cm in size and remains active for about 6 months (corpus luteum graviditatis). If pregnancy does not occur, it degenerates after 8-10 days (luteolysis).