Final answer:
The luteal phase is the postovulatory phase of the menstrual cycle, characterized by the secretion of progesterone and estrogen from the corpus luteum, and lasts approximately 14 days in a typical 28-day cycle.
Step-by-step explanation:
The luteal phase is the postovulatory phase of the menstrual cycle, which follows ovulation. After an egg is released from the ovary during ovulation, the remains of the follicle transform into a structure known as the corpus luteum, which is critical during the luteal phase. The corpus luteum secretes important hormones, such as progesterone and estrogen, to prepare the uterus for a potential pregnancy. In a typical 28-day cycle, this phase lasts about 14 days, starting from approximately day 15 to day 28.
If fertilization does not occur, the corpus luteum degenerates into a corpus albicans, leading to a decline in progesterone and estrogen levels. This hormonal decline signals the end of the luteal phase and triggers the next menstrual cycle, starting with the menses phase where the lining of the uterus is shed.