Between menarche and menopause the human ovaries regularly alternate between luteal and follicular phases during the monthly menstrual cycle. Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood flow stop and the uterus lining thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one, or occasionally two, become dominant, while non-dominant follicles shrink and die. About mid-cycle, some 10–12 hours after the luteinizing hormone (LH) surges, the dominant follicle releases an oocyte, in an event called ovulation.