The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis.
Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth.
These cells start division and enter into prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes.
Primary oocytes get surrounded by granulosa cells to form Primary follicles. Primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles.
The secondary follicle soon transforms into a tertiary follicle
The tertiary follicle further changes into the mature follicle or Graafian follicle.
Explanation:
The Corpus luteum is a structure formed from the Graffian follicle. After Ovulation, the ruptured Graffian follicle gets transformed into the Corpus luteum.
The Corpus luteum gets stimulated by the rising levels of LH and starts secreting the Progesterone hormone.
Progesterone inhibits the uterine contraction so that the pregnancy can be maintained. For this reason, it is called the pregnancy hormone.
In case if pregnancy does not occur after ovulation the levels of progesterone fall down and Corpus luteum gets transformed into Corpus albicans.