Schematic illustration of an ovary. The round ovary (on the left) is encompassed by the fimbrial funnel (infundibulum tubae uterinae), which leads the egg cell into the uterine tube and thus into the uterus. The illustration shows the maturing of the follicles (Graafian follicle), a corpus luteum, and a corpus albicans. The ovarian follicles consist of egg cell and follicle cells. According to their stage of development, they are classified as primordial, primary, secondary, tertiary, or Graafian follicles. During the ejection of the egg cell, estrogen (a steroid hormone) is released. Later on, the corpus luteum will produce progesteron.