The Ovary is divided into the cortex or cortical region and the medulla.

The ovarian surface is covered by a single layer of cuboidal, and in some parts squamous, cells. This layer is erroneously (and still) called ‘germinal epithelium’. Primordial germ cells are extra gonadal in origin. They migrate from the embryonic yolk sac into the cortex of the embryonic ovary. The dense connective tissue layer tunica albuginea lies between the germinal epithelium and the underlying cortex.

Ovarian follicles provide the micro-environment for the developing oocyte. At puberty, the initiation of the menstrual cycle (menarche) occurs. The follicles grow and mature, and a cyclic pattern of follicular maturation and ovulation is then established.

The corpus luteum forms after ovulation when the collapsed follicle differentiates into this new function unit. It is formed from granulosa and theca interna cells. Bleeding from the capillaries in theca interna occurs into the follicular lumen, and it is then called the corpus hemorrhagicum (has a central clot). The follicular cavity is then invaded by connective tissue from the stroma. Granulosa cells and theca interna cells differentiate to form granulosa luteal cells and theca luteal cells, called luteinization. There are two types of luteal cells:

The hormones prepare the uterus for implantation of the zygote (in the event of fertilization). After successful fertilization and implantation, the corpus luteum is maintain and continues to secrete progesterone and estrogen. The existence and function depends on the luteotropins human chorionic gonadotropin (hCG), LH, prolactin, and insulin (hCG is initially produced by the embryo and later by the placenta). Should fertilization and implantation not occur, the corpus luteum remains active only for 14 days (then called the corpus luteum of menstruation). The lack of hCG and luteotropins declines secretion of estrogen and progesteron. The corpus luteum degenerates and involutes 10 to 20 days after ovulation.The cells become loaded with lipid, decrease in size and undergo autolysis. A white scar is formed called the corpus albicans, which sinks deeper into the cortex and disappears over several months.