Luteinization refers to the process by which ovarian follicles develop into structures called corpus luteum. The corpus luteum is a temporary endocrine gland that forms in the ovary after the release of an egg during ovulation.

During a menstrual cycle, multiple follicles begin to develop in the ovary under the influence of follicle-stimulating hormone (FSH) released by the pituitary gland. These follicles contain eggs and produce the hormone estrogen. As the cycle progresses, one dominant follicle typically emerges and continues to mature.

When the dominant follicle reaches its maturation stage, it releases a surge of luteinizing hormone (LH), also released by the pituitary gland. The surge of LH triggers ovulation, the release of the egg from the follicle.

After ovulation, the remaining portion of the follicle transforms into the corpus luteum. The corpus luteum is a yellowish, hormone-secreting structure that produces progesterone, a hormone necessary for preparing the uterus for potential implantation of a fertilized egg.

Under the influence of LH, the granulosa cells of the follicle undergo a process called luteinization, which involves changes in cell structure and function. The luteinized granulosa cells, along with theca cells, form the corpus luteum. These cells begin to produce and secrete progesterone, which helps maintain the endometrium (lining of the uterus) in preparation for a possible pregnancy.

If fertilization occurs, the developing embryo releases a hormone called human chorionic gonadotropin (hCG). hCG supports the corpus luteum, preventing its degradation and allowing it to continue producing progesterone to support the pregnancy. Eventually, the placenta takes over the production of progesterone.

If fertilization does not occur, the corpus luteum undergoes a process called luteolysis, where it degenerates and reduces its hormone production. The declining levels of progesterone trigger the shedding of the uterine lining during menstruation, marking the beginning of a new menstrual cycle.

In summary, luteinization is the process by which the ovarian follicle transforms into the corpus luteum after ovulation. The corpus luteum produces progesterone, which plays a crucial role in the preparation and maintenance of the uterine lining during the menstrual cycle.

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