The image shows a schematic illustration of the ovary. The round ovary (on the left) is encompassed by the fimbrial funnel (infundibulum tubae uterinae) that guides the ovum into the uterine tube and thus into the uterus. It specifically shows the maturing of the vesicular ovarian follicles (Graaf follicle) as well as a corpus luteum (yellow) and a corpus albicans (white). The ovarian follicles consists of the egg cell and follicular cells. Depending on the development stage, they are called primordial, primary, secondary, tertiary, or Graaf follicle. When the ovulation happens, estrogen (a steroid hormone) is released. Later on, the corpus luteum will produce progesterone.