What phase of the menstrual cycle is characterized by the formation of the corpus luteum?

The formation of the corpus luteum occurs during the luteal phase of the menstrual cycle. After ovulation, which is the release of an egg from the ovary, the ruptured follicle transforms into the corpus luteum. This structure is crucial because it produces hormones, primarily progesterone, which helps maintain the uterine lining in preparation for a possible implantation of a fertilized egg. If fertilization does not occur, the corpus luteum degenerates, leading to a decrease in hormone levels and the eventual onset of menstruation. Understanding this process is essential in comprehending the hormonal regulation and phases of the menstrual cycle.